1.
System of measurement
–
A system of measurement is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce, systems of measurement in modern use include the metric system, the imperial system, and United States customary units. The French Revolution gave rise to the system, and this has spread around the world. In most systems, length, mass, and time are base quantities, later science developments showed that either electric charge or electric current could be added to extend the set of base quantities by which many other metrological units could be easily defined. Other quantities, such as power and speed, are derived from the set, for example. Such arrangements were satisfactory in their own contexts, the preference for a more universal and consistent system only gradually spread with the growth of science. Changing a measurement system has substantial financial and cultural costs which must be offset against the advantages to be obtained using a more rational system. However pressure built up, including scientists and engineers for conversion to a more rational. The unifying characteristic is that there was some definition based on some standard, eventually cubits and strides gave way to customary units to met the needs of merchants and scientists. In the metric system and other recent systems, a basic unit is used for each base quantity. Often secondary units are derived from the units by multiplying by powers of ten. Thus the basic unit of length is the metre, a distance of 1.234 m is 1,234 millimetres. Metrication is complete or nearly complete in almost all countries, US customary units are heavily used in the United States and to some degree in Liberia. Traditional Burmese units of measurement are used in Burma, U. S. units are used in limited contexts in Canada due to the large volume of trade, there is also considerable use of Imperial weights and measures, despite de jure Canadian conversion to metric. In the United States, metric units are used almost universally in science, widely in the military, and partially in industry, but customary units predominate in household use. At retail stores, the liter is a used unit for volume, especially on bottles of beverages. Some other standard non-SI units are still in use, such as nautical miles and knots in aviation. Metric systems of units have evolved since the adoption of the first well-defined system in France in 1795, during this evolution the use of these systems has spread throughout the world, first to non-English-speaking countries, and then to English speaking countries
2.
SI derived unit
–
The International System of Units specifies a set of seven base units from which all other SI units of measurement are derived. Each of these units is either dimensionless or can be expressed as a product of powers of one or more of the base units. For example, the SI derived unit of area is the metre. The degree Celsius has an unclear status, and is arguably an exception to this rule. The names of SI units are written in lowercase, the symbols for units named after persons, however, are always written with an uppercase initial letter. In addition to the two dimensionless derived units radian and steradian,20 other derived units have special names, some other units such as the hour, litre, tonne, bar and electronvolt are not SI units, but are widely used in conjunction with SI units. Until 1995, the SI classified the radian and the steradian as supplementary units, but this designation was abandoned, International System of Quantities International System of Units International Vocabulary of Metrology Metric prefix Metric system Non-SI units mentioned in the SI Planck units SI base unit I. Mills, Tomislav Cvitas, Klaus Homann, Nikola Kallay, IUPAC, Quantities, Units and Symbols in Physical Chemistry. CS1 maint, Multiple names, authors list
3.
Power (physics)
–
In physics, power is the rate of doing work. It is the amount of energy consumed per unit time, having no direction, it is a scalar quantity. In the SI system, the unit of power is the joule per second, known as the watt in honour of James Watt, another common and traditional measure is horsepower. Being the rate of work, the equation for power can be written, because this integral depends on the trajectory of the point of application of the force and torque, this calculation of work is said to be path dependent. As a physical concept, power requires both a change in the universe and a specified time in which the change occurs. This is distinct from the concept of work, which is measured in terms of a net change in the state of the physical universe. The output power of a motor is the product of the torque that the motor generates. The power involved in moving a vehicle is the product of the force of the wheels. The dimension of power is divided by time. The SI unit of power is the watt, which is equal to one joule per second, other units of power include ergs per second, horsepower, metric horsepower, and foot-pounds per minute. One horsepower is equivalent to 33,000 foot-pounds per minute, or the required to lift 550 pounds by one foot in one second. Other units include dBm, a logarithmic measure with 1 milliwatt as reference, food calories per hour, Btu per hour. This shows how power is an amount of energy consumed per unit time. If ΔW is the amount of work performed during a period of time of duration Δt and it is the average amount of work done or energy converted per unit of time. The average power is simply called power when the context makes it clear. The instantaneous power is then the value of the average power as the time interval Δt approaches zero. P = lim Δ t →0 P a v g = lim Δ t →0 Δ W Δ t = d W d t. In the case of constant power P, the amount of work performed during a period of duration T is given by, W = P t
4.
James Watt
–
While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. He realised that contemporary engine designs wasted a great deal of energy by repeatedly cooling and reheating the cylinder, Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. Eventually he adapted his engine to produce rotary motion, greatly broadening its use beyond pumping water, Watt attempted to commercialise his invention, but experienced great financial difficulties until he entered a partnership with Matthew Boulton in 1775. The new firm of Boulton and Watt was eventually highly successful, in his retirement, Watt continued to develop new inventions though none was as significant as his steam engine work. He developed the concept of horsepower, and the SI unit of power, James Watt was born on 19 January 1736 in Greenock, Renfrewshire, a seaport on the Firth of Clyde. His father was a shipwright, ship owner and contractor, and served as the towns chief baillie, while his mother, Agnes Muirhead, both were Presbyterians and strong Covenanters. Watts grandfather, Thomas Watt, was a teacher and baillie to the Baron of Cartsburn. Despite being raised by parents, he later on became a deist. Watt did not attend regularly, initially he was mostly schooled at home by his mother but later he attended Greenock Grammar School. He exhibited great manual dexterity, engineering skills and an aptitude for mathematics, while Latin, when he was eighteen, his mother died and his fathers health began to fail. Watt travelled to London to study instrument-making for a year, then returned to Scotland and he made and repaired brass reflecting quadrants, parallel rulers, scales, parts for telescopes, and barometers, among other things. Because he had not served at least seven years as an apprentice, Watt was saved from this impasse by the arrival from Jamaica of astronomical instruments bequeathed by Alexander Macfarlane to the University of Glasgow, instruments that required expert attention. Watt restored them to working order and was remunerated and these instruments were eventually installed in the Macfarlane Observatory. Subsequently three professors offered him the opportunity to set up a workshop within the university. It was initiated in 1757 and two of the professors, the physicist and chemist Joseph Black as well as the famed Adam Smith, at first he worked on maintaining and repairing scientific instruments used in the university, helping with demonstrations, and expanding the production of quadrants. In 1759 he formed a partnership with John Craig, an architect and businessman, to manufacture and sell a line of products including musical instruments and this partnership lasted for the next six years, and employed up to sixteen workers. One employee, Alex Gardner, eventually took over the business, in 1764, Watt married his cousin Margaret Miller, with whom he had five children, two of whom lived to adulthood, James Jr. and Margaret. His wife died in childbirth in 1772, in 1777 he was married again, to Ann MacGregor, daughter of a Glasgow dye-maker, with whom he had two children, Gregory, who became a geologist and mineralogist, and Janet
5.
SI base unit
–
The International System of Units defines seven units of measure as a basic set from which all other SI units can be derived. The SI base units form a set of mutually independent dimensions as required by dimensional analysis commonly employed in science, thus, the kelvin, named after Lord Kelvin, has the symbol K and the ampere, named after André-Marie Ampère, has the symbol A. Many other units, such as the litre, are not part of the SI. The definitions of the units have been modified several times since the Metre Convention in 1875. Since the redefinition of the metre in 1960, the kilogram is the unit that is directly defined in terms of a physical artifact. However, the mole, the ampere, and the candela are linked through their definitions to the mass of the platinum–iridium cylinder stored in a vault near Paris. It has long been an objective in metrology to define the kilogram in terms of a fundamental constant, two possibilities have attracted particular attention, the Planck constant and the Avogadro constant. The 23rd CGPM decided to postpone any formal change until the next General Conference in 2011
6.
Kilogram
–
The kilogram or kilogramme is the base unit of mass in the International System of Units and is defined as being equal to the mass of the International Prototype of the Kilogram. The avoirdupois pound, used in both the imperial and US customary systems, is defined as exactly 0.45359237 kg, making one kilogram approximately equal to 2.2046 avoirdupois pounds. Other traditional units of weight and mass around the world are also defined in terms of the kilogram, the gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimeter of water at the melting point of ice. The final kilogram, manufactured as a prototype in 1799 and from which the IPK was derived in 1875, had an equal to the mass of 1 dm3 of water at its maximum density. The kilogram is the only SI base unit with an SI prefix as part of its name and it is also the only SI unit that is still directly defined by an artifact rather than a fundamental physical property that can be reproduced in different laboratories. Three other base units and 17 derived units in the SI system are defined relative to the kilogram, only 8 other units do not require the kilogram in their definition, temperature, time and frequency, length, and angle. At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, the decision was originally deferred until 2014, in 2014 it was deferred again until the next meeting. There are currently several different proposals for the redefinition, these are described in the Proposed Future Definitions section below, the International Prototype Kilogram is rarely used or handled. In the decree of 1795, the term gramme thus replaced gravet, the French spelling was adopted in the United Kingdom when the word was used for the first time in English in 1797, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with kilogram having become by far the more common, UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has used to mean both kilogram and kilometer. In 1935 this was adopted by the IEC as the Giorgi system, now known as MKS system. In 1948 the CGPM commissioned the CIPM to make recommendations for a practical system of units of measurement. This led to the launch of SI in 1960 and the subsequent publication of the SI Brochure, the kilogram is a unit of mass, a property which corresponds to the common perception of how heavy an object is. Mass is a property, that is, it is related to the tendency of an object at rest to remain at rest, or if in motion to remain in motion at a constant velocity. Accordingly, for astronauts in microgravity, no effort is required to hold objects off the cabin floor, they are weightless. However, since objects in microgravity still retain their mass and inertia, the ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7,1795, the gram was decreed in France to be the weight of a volume of pure water equal to the cube of the hundredth part of the metre
7.
Metre
–
The metre or meter, is the base unit of length in the International System of Units. The metre is defined as the length of the path travelled by light in a vacuum in 1/299792458 seconds, the metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole. In 1799, it was redefined in terms of a metre bar. In 1960, the metre was redefined in terms of a number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted, the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Measuring devices are spelled -meter in all variants of English, the suffix -meter has the same Greek origin as the unit of length. This range of uses is found in Latin, French, English. Thus calls for measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. In 1668, Wilkins proposed using Christopher Wrens suggestion of defining the metre using a pendulum with a length which produced a half-period of one second, christiaan Huygens had observed that length to be 38 Rijnland inches or 39.26 English inches. This is the equivalent of what is now known to be 997 mm, no official action was taken regarding this suggestion. In the 18th century, there were two approaches to the definition of the unit of length. One favoured Wilkins approach, to define the metre in terms of the length of a pendulum which produced a half-period of one second. The other approach was to define the metre as one ten-millionth of the length of a quadrant along the Earths meridian, that is, the distance from the Equator to the North Pole. This means that the quadrant would have defined as exactly 10000000 metres at that time. To establish a universally accepted foundation for the definition of the metre, more measurements of this meridian were needed. This portion of the meridian, assumed to be the length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator
8.
Second
–
The second is the base unit of time in the International System of Units. It is qualitatively defined as the division of the hour by sixty. SI definition of second is the duration of 9192631770 periods of the corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. Seconds may be measured using a mechanical, electrical or an atomic clock, SI prefixes are combined with the word second to denote subdivisions of the second, e. g. the millisecond, the microsecond, and the nanosecond. Though SI prefixes may also be used to form multiples of the such as kilosecond. The second is also the unit of time in other systems of measurement, the centimetre–gram–second, metre–kilogram–second, metre–tonne–second. Absolute zero implies no movement, and therefore zero external radiation effects, the second thus defined is consistent with the ephemeris second, which was based on astronomical measurements. The realization of the second is described briefly in a special publication from the National Institute of Standards and Technology. 1 international second is equal to, 1⁄60 minute 1⁄3,600 hour 1⁄86,400 day 1⁄31,557,600 Julian year 1⁄, more generally, = 1⁄, the Hellenistic astronomers Hipparchus and Ptolemy subdivided the day into sixty parts. They also used an hour, simple fractions of an hour. No sexagesimal unit of the day was used as an independent unit of time. The modern second is subdivided using decimals - although the third remains in some languages. The earliest clocks to display seconds appeared during the last half of the 16th century, the second became accurately measurable with the development of mechanical clocks keeping mean time, as opposed to the apparent time displayed by sundials. The earliest spring-driven timepiece with a hand which marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection. During the 3rd quarter of the 16th century, Taqi al-Din built a clock with marks every 1/5 minute, in 1579, Jost Bürgi built a clock for William of Hesse that marked seconds. In 1581, Tycho Brahe redesigned clocks that displayed minutes at his observatory so they also displayed seconds, however, they were not yet accurate enough for seconds. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds, in 1670, London clockmaker William Clement added this seconds pendulum to the original pendulum clock of Christiaan Huygens. From 1670 to 1680, Clement made many improvements to his clock and this clock used an anchor escapement mechanism with a seconds pendulum to display seconds in a small subdial
9.
International System of Units
–
The International System of Units is the modern form of the metric system, and is the most widely used system of measurement. It comprises a coherent system of units of measurement built on seven base units, the system also establishes a set of twenty prefixes to the unit names and unit symbols that may be used when specifying multiples and fractions of the units. The system was published in 1960 as the result of an initiative began in 1948. It is based on the system of units rather than any variant of the centimetre-gram-second system. The motivation for the development of the SI was the diversity of units that had sprung up within the CGS systems, the International System of Units has been adopted by most developed countries, however, the adoption has not been universal in all English-speaking countries. The metric system was first implemented during the French Revolution with just the metre and kilogram as standards of length, in the 1830s Carl Friedrich Gauss laid the foundations for a coherent system based on length, mass, and time. In the 1860s a group working under the auspices of the British Association for the Advancement of Science formulated the requirement for a coherent system of units with base units and derived units. Meanwhile, in 1875, the Treaty of the Metre passed responsibility for verification of the kilogram, in 1921, the Treaty was extended to include all physical quantities including electrical units originally defined in 1893. The units associated with these quantities were the metre, kilogram, second, ampere, kelvin, in 1971, a seventh base quantity, amount of substance represented by the mole, was added to the definition of SI. On 11 July 1792, the proposed the names metre, are, litre and grave for the units of length, area, capacity. The committee also proposed that multiples and submultiples of these units were to be denoted by decimal-based prefixes such as centi for a hundredth, on 10 December 1799, the law by which the metric system was to be definitively adopted in France was passed. Prior to this, the strength of the magnetic field had only been described in relative terms. The technique used by Gauss was to equate the torque induced on a magnet of known mass by the earth’s magnetic field with the torque induced on an equivalent system under gravity. The resultant calculations enabled him to assign dimensions based on mass, length, a French-inspired initiative for international cooperation in metrology led to the signing in 1875 of the Metre Convention. Initially the convention only covered standards for the metre and the kilogram, one of each was selected at random to become the International prototype metre and International prototype kilogram that replaced the mètre des Archives and kilogramme des Archives respectively. Each member state was entitled to one of each of the prototypes to serve as the national prototype for that country. Initially its prime purpose was a periodic recalibration of national prototype metres. The official language of the Metre Convention is French and the version of all official documents published by or on behalf of the CGPM is the French-language version
10.
Joule
–
The joule, symbol J, is a derived unit of energy in the International System of Units. It is equal to the transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one metre. It is also the energy dissipated as heat when a current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule, one joule can also be defined as, The work required to move an electric charge of one coulomb through an electrical potential difference of one volt, or one coulomb volt. This relationship can be used to define the volt, the work required to produce one watt of power for one second, or one watt second. This relationship can be used to define the watt and this SI unit is named after James Prescott Joule. As with every International System of Units unit named for a person, note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. The CGPM has given the unit of energy the name Joule, the use of newton metres for torque and joules for energy is helpful to avoid misunderstandings and miscommunications. The distinction may be also in the fact that energy is a scalar – the dot product of a vector force. By contrast, torque is a vector – the cross product of a distance vector, torque and energy are related to one another by the equation E = τ θ, where E is energy, τ is torque, and θ is the angle swept. Since radians are dimensionless, it follows that torque and energy have the same dimensions, one joule in everyday life represents approximately, The energy required to lift a medium-size tomato 1 m vertically from the surface of the Earth. The energy released when that same tomato falls back down to the ground, the energy required to accelerate a 1 kg mass at 1 m·s−2 through a 1 m distance in space. The heat required to raise the temperature of 1 g of water by 0.24 °C, the typical energy released as heat by a person at rest every 1/60 s. The kinetic energy of a 50 kg human moving very slowly, the kinetic energy of a 56 g tennis ball moving at 6 m/s. The kinetic energy of an object with mass 1 kg moving at √2 ≈1.4 m/s, the amount of electricity required to light a 1 W LED for 1 s. Since the joule is also a watt-second and the unit for electricity sales to homes is the kW·h. For additional examples, see, Orders of magnitude The zeptojoule is equal to one sextillionth of one joule,160 zeptojoules is equivalent to one electronvolt. The nanojoule is equal to one billionth of one joule, one nanojoule is about 1/160 of the kinetic energy of a flying mosquito
11.
Dimensional analysis
–
Converting from one dimensional unit to another is often somewhat complex. Dimensional analysis, or more specifically the method, also known as the unit-factor method, is a widely used technique for such conversions using the rules of algebra. The concept of physical dimension was introduced by Joseph Fourier in 1822, Physical quantities that are measurable have the same dimension and can be directly compared to each other, even if they are originally expressed in differing units of measure. If physical quantities have different dimensions, they cannot be compared by similar units, hence, it is meaningless to ask whether a kilogram is greater than, equal to, or less than an hour. Any physically meaningful equation will have the dimensions on their left and right sides. Checking for dimensional homogeneity is an application of dimensional analysis. Dimensional analysis is routinely used as a check of the plausibility of derived equations and computations. It is generally used to categorize types of quantities and units based on their relationship to or dependence on other units. Many parameters and measurements in the sciences and engineering are expressed as a concrete number – a numerical quantity. Often a quantity is expressed in terms of other quantities, for example, speed is a combination of length and time. Compound relations with per are expressed with division, e. g.60 mi/1 h, other relations can involve multiplication, powers, or combinations thereof. A base unit is a unit that cannot be expressed as a combination of other units, for example, units for length and time are normally chosen as base units. Units for volume, however, can be factored into the units of length. Sometimes the names of units obscure that they are derived units, for example, an ampere is a unit of electric current, which is equivalent to electric charge per unit time and is measured in coulombs per second, so 1 A =1 C/s. Similarly, one newton is 1 kg⋅m/s2, percentages are dimensionless quantities, since they are ratios of two quantities with the same dimensions. In other words, the % sign can be read as 1/100, derivatives with respect to a quantity add the dimensions of the variable one is differentiating with respect to on the denominator. Thus, position has the dimension L, derivative of position with respect to time has dimension LT−1 – length from position, time from the derivative, the second derivative has dimension LT−2. In economics, one distinguishes between stocks and flows, a stock has units of units, while a flow is a derivative of a stock, in some contexts, dimensional quantities are expressed as dimensionless quantities or percentages by omitting some dimensions
12.
Velocity
–
The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of its speed and direction of motion, Velocity is an important concept in kinematics, the branch of classical mechanics that describes the motion of bodies. Velocity is a vector quantity, both magnitude and direction are needed to define it. The scalar absolute value of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI system as metres per second or as the SI base unit of. For example,5 metres per second is a scalar, whereas 5 metres per second east is a vector, if there is a change in speed, direction or both, then the object has a changing velocity and is said to be undergoing an acceleration. To have a constant velocity, an object must have a constant speed in a constant direction, constant direction constrains the object to motion in a straight path thus, a constant velocity means motion in a straight line at a constant speed. For example, a car moving at a constant 20 kilometres per hour in a path has a constant speed. Hence, the car is considered to be undergoing an acceleration, Speed describes only how fast an object is moving, whereas velocity gives both how fast and in what direction the object is moving. If a car is said to travel at 60 km/h, its speed has been specified, however, if the car is said to move at 60 km/h to the north, its velocity has now been specified. The big difference can be noticed when we consider movement around a circle and this is because the average velocity is calculated by only considering the displacement between the starting and the end points while the average speed considers only the total distance traveled. Velocity is defined as the rate of change of position with respect to time, average velocity can be calculated as, v ¯ = Δ x Δ t. The average velocity is less than or equal to the average speed of an object. This can be seen by realizing that while distance is always strictly increasing, from this derivative equation, in the one-dimensional case it can be seen that the area under a velocity vs. time is the displacement, x. In calculus terms, the integral of the velocity v is the displacement function x. In the figure, this corresponds to the area under the curve labeled s. Since the derivative of the position with respect to time gives the change in position divided by the change in time, although velocity is defined as the rate of change of position, it is often common to start with an expression for an objects acceleration. As seen by the three green tangent lines in the figure, an objects instantaneous acceleration at a point in time is the slope of the tangent to the curve of a v graph at that point. In other words, acceleration is defined as the derivative of velocity with respect to time, from there, we can obtain an expression for velocity as the area under an a acceleration vs. time graph
13.
Newton (unit)
–
The newton is the International System of Units derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, see below for the conversion factors. One newton is the force needed to one kilogram of mass at the rate of one metre per second squared in direction of the applied force. In 1948, the 9th CGPM resolution 7 adopted the name newton for this force, the MKS system then became the blueprint for todays SI system of units. The newton thus became the unit of force in le Système International dUnités. This SI unit is named after Isaac Newton, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. Newtons second law of motion states that F = ma, where F is the applied, m is the mass of the object receiving the force. The newton is therefore, where the symbols are used for the units, N for newton, kg for kilogram, m for metre. In dimensional analysis, F = M L T2 where F is force, M is mass, L is length, at average gravity on earth, a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apples weight, for example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN. One kilonewton,1 kN, is 102.0 kgf,1 kN =102 kg ×9.81 m/s2 So for example, a platform rated at 321 kilonewtons will safely support a 32,100 kilograms load. Specifications in kilonewtons are common in safety specifications for, the values of fasteners, Earth anchors. Working loads in tension and in shear, thrust of rocket engines and launch vehicles clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts
14.
Work (physics)
–
In physics, a force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force. For example, when a ball is held above the ground and then dropped, the SI unit of work is the joule. The SI unit of work is the joule, which is defined as the work expended by a force of one newton through a distance of one metre. The dimensionally equivalent newton-metre is sometimes used as the unit for work, but this can be confused with the unit newton-metre. Usage of N⋅m is discouraged by the SI authority, since it can lead to confusion as to whether the quantity expressed in newton metres is a torque measurement, or a measurement of energy. Non-SI units of work include the erg, the foot-pound, the foot-poundal, the hour, the litre-atmosphere. Due to work having the physical dimension as heat, occasionally measurement units typically reserved for heat or energy content, such as therm, BTU. The work done by a constant force of magnitude F on a point that moves a distance s in a line in the direction of the force is the product W = F s. For example, if a force of 10 newtons acts along a point that travels 2 meters and this is approximately the work done lifting a 1 kg weight from ground level to over a persons head against the force of gravity. Notice that the work is doubled either by lifting twice the weight the distance or by lifting the same weight twice the distance. Work is closely related to energy, the work-energy principle states that an increase in the kinetic energy of a rigid body is caused by an equal amount of positive work done on the body by the resultant force acting on that body. Conversely, a decrease in energy is caused by an equal amount of negative work done by the resultant force. From Newtons second law, it can be shown that work on a free, rigid body, is equal to the change in energy of the velocity and rotation of that body. The work of forces generated by a function is known as potential energy. These formulas demonstrate that work is the associated with the action of a force, so work subsequently possesses the physical dimensions. The work/energy principles discussed here are identical to Electric work/energy principles, constraint forces determine the movement of components in a system, constraining the object within a boundary. Constraint forces ensure the velocity in the direction of the constraint is zero and this only applies for a single particle system. For example, in an Atwood machine, the rope does work on each body, there are, however, cases where this is not true
15.
Electromagnetism
–
Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force usually exhibits electromagnetic fields such as fields, magnetic fields. The other three fundamental interactions are the interaction, the weak interaction, and gravitation. The word electromagnetism is a form of two Greek terms, ἤλεκτρον, ēlektron, amber, and μαγνῆτις λίθος magnētis lithos, which means magnesian stone. The electromagnetic force plays a role in determining the internal properties of most objects encountered in daily life. Ordinary matter takes its form as a result of forces between individual atoms and molecules in matter, and is a manifestation of the electromagnetic force. Electrons are bound by the force to atomic nuclei, and their orbital shapes. The electromagnetic force governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, there are numerous mathematical descriptions of the electromagnetic field. In classical electrodynamics, electric fields are described as electric potential, although electromagnetism is considered one of the four fundamental forces, at high energy the weak force and electromagnetic force are unified as a single electroweak force. In the history of the universe, during the epoch the unified force broke into the two separate forces as the universe cooled. Originally, electricity and magnetism were considered to be two separate forces, Magnetic poles attract or repel one another in a manner similar to positive and negative charges and always exist as pairs, every north pole is yoked to a south pole. An electric current inside a wire creates a corresponding magnetic field outside the wire. Its direction depends on the direction of the current in the wire. A current is induced in a loop of wire when it is moved toward or away from a field, or a magnet is moved towards or away from it. While preparing for a lecture on 21 April 1820, Hans Christian Ørsted made a surprising observation. As he was setting up his materials, he noticed a compass needle deflected away from north when the electric current from the battery he was using was switched on. At the time of discovery, Ørsted did not suggest any explanation of the phenomenon. However, three later he began more intensive investigations
16.
Ampere
–
The ampere, often shortened to amp, is a unit of electric current. In the International System of Units the ampere is one of the seven SI base units and it is named after André-Marie Ampère, French mathematician and physicist, considered the father of electrodynamics. SI defines the ampere in terms of base units by measuring the electromagnetic force between electrical conductors carrying electric current. The ampere was then defined as one coulomb of charge per second, in SI, the unit of charge, the coulomb, is defined as the charge carried by one ampere during one second. In the future, the SI definition may shift back to charge as the base unit, ampères force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the definition of the ampere. The SI unit of charge, the coulomb, is the quantity of electricity carried in 1 second by a current of 1 ampere, conversely, a current of one ampere is one coulomb of charge going past a given point per second,1 A =1 C s. In general, charge Q is determined by steady current I flowing for a time t as Q = It, constant, instantaneous and average current are expressed in amperes and the charge accumulated, or passed through a circuit over a period of time is expressed in coulombs. The relation of the ampere to the coulomb is the same as that of the watt to the joule, the ampere was originally defined as one tenth of the unit of electric current in the centimetre–gram–second system of units. That unit, now known as the abampere, was defined as the amount of current that generates a force of two dynes per centimetre of length between two wires one centimetre apart. The size of the unit was chosen so that the derived from it in the MKSA system would be conveniently sized. The international ampere was a realization of the ampere, defined as the current that would deposit 0.001118 grams of silver per second from a silver nitrate solution. Later, more accurate measurements revealed that this current is 0.99985 A, at present, techniques to establish the realization of an ampere have a relative uncertainty of approximately a few parts in 107, and involve realizations of the watt, the ohm and the volt. Rather than a definition in terms of the force between two current-carrying wires, it has proposed that the ampere should be defined in terms of the rate of flow of elementary charges. Since a coulomb is equal to 6. 2415093×1018 elementary charges. The proposed change would define 1 A as being the current in the direction of flow of a number of elementary charges per second. In 2005, the International Committee for Weights and Measures agreed to study the proposed change, the new definition was discussed at the 25th General Conference on Weights and Measures in 2014 but for the time being was not adopted. The current drawn by typical constant-voltage energy distribution systems is usually dictated by the power consumed by the system, for this reason the examples given below are grouped by voltage level
17.
Voltage
–
Voltage, electric potential difference, electric pressure or electric tension is the difference in electric potential energy between two points per unit electric charge. The voltage between two points is equal to the work done per unit of charge against an electric field to move the test charge between two points. This is measured in units of volts, voltage can be caused by static electric fields, by electric current through a magnetic field, by time-varying magnetic fields, or some combination of these three. A voltmeter can be used to measure the voltage between two points in a system, often a reference potential such as the ground of the system is used as one of the points. A voltage may represent either a source of energy or lost, used, given two points in space, x A and x B, voltage is the difference in electric potential between those two points. Electric potential must be distinguished from electric energy by noting that the potential is a per-unit-charge quantity. Like mechanical potential energy, the zero of electric potential can be chosen at any point, so the difference in potential, i. e. the voltage, is the quantity which is physically meaningful. The voltage between point A to point B is equal to the work which would have to be done, per unit charge, against or by the electric field to move the charge from A to B. The voltage between the two ends of a path is the energy required to move a small electric charge along that path. Mathematically this is expressed as the integral of the electric field. In the general case, both an electric field and a dynamic electromagnetic field must be included in determining the voltage between two points. Historically this quantity has also called tension and pressure. Pressure is now obsolete but tension is used, for example within the phrase high tension which is commonly used in thermionic valve based electronics. Voltage is defined so that negatively charged objects are pulled towards higher voltages, therefore, the conventional current in a wire or resistor always flows from higher voltage to lower voltage. Current can flow from lower voltage to higher voltage, but only when a source of energy is present to push it against the electric field. This is the case within any electric power source, for example, inside a battery, chemical reactions provide the energy needed for ion current to flow from the negative to the positive terminal. The electric field is not the only factor determining charge flow in a material, the electric potential of a material is not even a well defined quantity, since it varies on the subatomic scale. A more convenient definition of voltage can be found instead in the concept of Fermi level, in this case the voltage between two bodies is the thermodynamic work required to move a unit of charge between them
18.
Volt
–
The volt is the derived unit for electric potential, electric potential difference, and electromotive force. One volt is defined as the difference in potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. It is also equal to the difference between two parallel, infinite planes spaced 1 meter apart that create an electric field of 1 newton per coulomb. Additionally, it is the difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can also be expressed as amperes times ohms, watts per ampere, or joules per coulomb, for the Josephson constant, KJ = 2e/h, the conventional value KJ-90 is used, K J-90 =0.4835979 GHz μ V. This standard is typically realized using an array of several thousand or tens of thousands of junctions. Empirically, several experiments have shown that the method is independent of device design, material, measurement setup, etc. in the water-flow analogy sometimes used to explain electric circuits by comparing them with water-filled pipes, voltage is likened to difference in water pressure. Current is proportional to the diameter of the pipe or the amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping, the relationship between voltage and current is defined by Ohms Law. Ohms Law is analogous to the Hagen–Poiseuille equation, as both are linear models relating flux and potential in their respective systems, the voltage produced by each electrochemical cell in a battery is determined by the chemistry of that cell. Cells can be combined in series for multiples of that voltage, mechanical generators can usually be constructed to any voltage in a range of feasibility. High-voltage electric power lines,110 kV and up Lightning, Varies greatly. Volta had determined that the most effective pair of metals to produce electricity was zinc. In 1861, Latimer Clark and Sir Charles Bright coined the name volt for the unit of resistance, by 1873, the British Association for the Advancement of Science had defined the volt, ohm, and farad. In 1881, the International Electrical Congress, now the International Electrotechnical Commission and they made the volt equal to 108 cgs units of voltage, the cgs system at the time being the customary system of units in science. At that time, the volt was defined as the difference across a conductor when a current of one ampere dissipates one watt of power. The international volt was defined in 1893 as 1/1.434 of the emf of a Clark cell and this definition was abandoned in 1908 in favor of a definition based on the international ohm and international ampere until the entire set of reproducible units was abandoned in 1948. Prior to the development of the Josephson junction voltage standard, the volt was maintained in laboratories using specially constructed batteries called standard cells
19.
Conversion of units
–
Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors. The process of conversion depends on the situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards, engineering judgment may include such factors as, The precision and accuracy of measurement and the associated uncertainty of measurement. The statistical confidence interval or tolerance interval of the initial measurement, the number of significant figures of the measurement. The intended use of the measurement including the engineering tolerances, historical definitions of the units and their derivatives used in old measurements, e. g. international foot vs. Some conversions from one system of units to another need to be exact and this is sometimes called soft conversion. It does not involve changing the configuration of the item being measured. By contrast, a conversion or an adaptive conversion may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system and it sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are allowed and used. A conversion factor is used to change the units of a quantity without changing its value. The unity bracket method of unit conversion consists of a fraction in which the denominator is equal to the numerator, because of the identity property of multiplication, the value of a number will not change as long as it is multiplied by one. Also, if the numerator and denominator of a fraction are equal to each other, so as long as the numerator and denominator of the fraction are equivalent, they will not affect the value of the measured quantity. There are many applications that offer the thousands of the various units with conversions. For example, the free software movement offers a command line utility GNU units for Linux and this article gives lists of conversion factors for each of a number of physical quantities, which are listed in the index. For each physical quantity, a number of different units are shown, Conversion between units in the metric system can be discerned by their prefixes and are thus not listed in this article. Exceptions are made if the unit is known by another name. Within each table, the units are listed alphabetically, and the SI units are highlighted, notes, See Weight for detail of mass/weight distinction and conversion
20.
Ohm's law
–
Ohms law states that the current through a conductor between two points is directly proportional to the voltage across the two points. More specifically, Ohms law states that the R in this relation is constant, independent of the current and he presented a slightly more complex equation than the one above to explain his experimental results. The above equation is the form of Ohms law. In physics, the term Ohms law is used to refer to various generalizations of the law originally formulated by Ohm. This reformulation of Ohms law is due to Gustav Kirchhoff, in January 1781, before Georg Ohms work, Henry Cavendish experimented with Leyden jars and glass tubes of varying diameter and length filled with salt solution. He measured the current by noting how strong a shock he felt as he completed the circuit with his body, Cavendish wrote that the velocity varied directly as the degree of electrification. He did not communicate his results to other scientists at the time, francis Ronalds delineated “intensity” and “quantity” for the dry pile – a high voltage source – in 1814 using a gold-leaf electrometer. He found for a dry pile that the relationship between the two parameters was not proportional under certain meteorological conditions, Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book Die galvanische Kette, mathematisch bearbeitet. He drew considerable inspiration from Fouriers work on heat conduction in the explanation of his work. For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a stable voltage source in terms of internal resistance. He used a galvanometer to measure current, and knew that the voltage between the terminals was proportional to the junction temperature. He then added test wires of varying length, diameter, from this, Ohm determined his law of proportionality and published his results. Ohms law was probably the most important of the early descriptions of the physics of electricity. We consider it almost obvious today, when Ohm first published his work, this was not the case, critics reacted to his treatment of the subject with hostility. They called his work a web of naked fancies and the German Minister of Education proclaimed that a professor who preached such heresies was unworthy to teach science, also, Ohms brother Martin, a mathematician, was battling the German educational system. These factors hindered the acceptance of Ohms work, and his work did not become widely accepted until the 1840s, fortunately, Ohm received recognition for his contributions to science well before he died. While the old term for electrical conductance, the mho, is used, a new name. The siemens is preferred in formal papers, Ohms work long preceded Maxwells equations and any understanding of frequency-dependent effects in AC circuits
21.
Ohm
–
The ohm is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm. The definition of the ohm was revised several times, today the definition of the ohm is expressed from the quantum Hall effect. In many cases the resistance of a conductor in ohms is approximately constant within a range of voltages, temperatures. In alternating current circuits, electrical impedance is also measured in ohms, the siemens is the SI derived unit of electric conductance and admittance, also known as the mho, it is the reciprocal of resistance in ohms. The power dissipated by a resistor may be calculated from its resistance, non-linear resistors have a value that may vary depending on the applied voltage. The rapid rise of electrotechnology in the last half of the 19th century created a demand for a rational, coherent, consistent, telegraphers and other early users of electricity in the 19th century needed a practical standard unit of measurement for resistance. Two different methods of establishing a system of units can be chosen. Various artifacts, such as a length of wire or a standard cell, could be specified as producing defined quantities for resistance, voltage. This latter method ensures coherence with the units of energy, defining a unit for resistance that is coherent with units of energy and time in effect also requires defining units for potential and current. Some early definitions of a unit of resistance, for example, the absolute-units system related magnetic and electrostatic quantities to metric base units of mass, time, and length. These units had the advantage of simplifying the equations used in the solution of electromagnetic problems. However, the CGS units turned out to have impractical sizes for practical measurements, various artifact standards were proposed as the definition of the unit of resistance. In 1860 Werner Siemens published a suggestion for a reproducible resistance standard in Poggendorffs Annalen der Physik und Chemie and he proposed a column of pure mercury, of one square millimetre cross section, one metre long, Siemens mercury unit. However, this unit was not coherent with other units, one proposal was to devise a unit based on a mercury column that would be coherent – in effect, adjusting the length to make the resistance one ohm. Not all users of units had the resources to carry out experiments to the required precision. The BAAS in 1861 appointed a committee including Maxwell and Thomson to report upon Standards of Electrical Resistance, in the third report of the committee,1864, the resistance unit is referred to as B. A. unit, or Ohmad. By 1867 the unit is referred to as simply Ohm, the B. A. ohm was intended to be 109 CGS units but owing to an error in calculations the definition was 1. 3% too small. The error was significant for preparation of working standards, on September 21,1881 the Congrès internationale délectriciens defined a practical unit of Ohm for the resistance, based on CGS units, using a mercury column at zero deg
22.
Carl Wilhelm Siemens
–
Sir Charles William Siemens FRSA was a German-born engineer and entrepreneur who for most of his life worked in Britain and later became a British subject. Siemens was born in the village of Lenthe, today part of Gehrden, near Hanover where his father, Christian Ferdinand Siemens, the Siemens family is an old family of Goslar which has been documented since 1384. His mother was Eleonore Deichmann, and William, or Carl Wilhelm, was the son of a family of fourteen children. Of his siblings, Ernst Werner Siemens, the fourth child and he was also the brother of Carl Heinrich von Siemens and a cousin of Alexander Siemens. He used to say that on March 19 of that year he took oath and he was knighted – becoming Sir William – a few months before his death. He died on the evening of Monday 19 November 1883, at nine oclock and was buried on Monday 26 November, in Kensal Green Cemetery, a glass window installed in Westminster Abbey in his honor commemorated him. In the autumn of 1838 when William was fifteen years old and he attended a highly respected School of Trade and Commerce, the Gewerbe-Schule Magdeburg. William had a close relationship with his eldest brother, Ernst Werner Siemens had decided to teach William mathematics so that he could learn English at school instead. This programme helped them both and Williams knowledge of English proved an advantage to them both. He went on to pass his examination easily, less than a year later, their mother died and their father soon afterwards in 1840. He was also able for a time to work with Wilhelm Weber. William was nearly nineteen when he left university to become an apprentice engineer and he also found time for more artistic pursuits such as taking dancing lessons and even painting a landscape of Nordhausen for the wife of the factory manager. His progress in the factory was so rapid that his two-year apprenticeship was cut down to one. Due to the education of the members of the family becoming a financial worry, on 10 March 1843. He was acting as an agent for his brother Werner, and he hoped to earn money by selling a patent in England to help support. He felt a desire to see England and the journey cost him £1. He was well aware, as he wrote to Werner, that his visit might achieve nothing and this indeed proved to be the case. Siemens had been trained as a engineer, and his most important work at this early stage was non-electrical, the greatest achievement of his life
23.
British Science Association
–
The British Science Association is a charity and learned society founded in 1831 to aid in the promotion and development of science. Until 2009 it was known as the British Association for the Advancement of Science, the Association was founded in 1831 and modelled on the German Gesellschaft Deutscher Naturforscher und Ärzte. The prime mover was Reverend William Vernon Harcourt, following a suggestion by Sir David Brewster, Brewster, Charles Babbage, William Whewell and J. F. W. Johnston are also considered to be founding members. The first meeting was held in York on Tuesday 27 September 1831 with various scientific papers being presented on the following days and it was chaired by Viscount Milton, President of the Yorkshire Philosophical Society, and upwards of 300 gentlemen attended the meeting. The newspaper published the names of over a hundred of those attending, from that date onwards a meeting was held annually at a place chosen at a previous meeting. In 1832, for example, the meeting was held in Oxford, by this stage the Association had four sections, Physics, Chemistry, Geology and Natural History. A very important decision in the Association’s history was made in 1842 when it was resolved to create a “physical observatory”, a building that became well known as the Kew Observatory was taken on for the purpose and Francis Ronalds was chosen as the inaugural Honorary Director. Kew Observatory quickly became one of the most renowned meteorological and geomagnetic observatories in the world, one of the most famous events linked to the Association Meeting was an exchange between Thomas Henry Huxley and Bishop Samuel Wilberforce in 1860. Although a number of newspapers made passing references to the exchange, a need for standards arose with the submarine telegraph industry. The undertaking was suggested to the BA by William Thomson, josiah Latimer Clark and Fleeming Jenkin made preparations. Thomson, with his students, found that copper, contaminated with arsenic. The chemist Augustus Matthiessen contributed an appendix to the final 1873 report that showed temperature-dependence of alloys, the Association introduced the British Association screw threads, a series of screw thread standards in sizes from 0. 25mm up to 6mm, in 1884. The standards were ahead of their time in that they were based on the metric system and they remained in general use for instruments and small assemblies until metrication in the 1970s. A decision that became notorious in the century was made in 1878 when a committee of the Association recommended against constructing Charles Babbages analytical engine. The Association was parodied by English novelist Charles Dickens as The Mudfog Society for the Advancement of Everything in The Mudfog Papers, the Associations main aim is to improve the perception of science and scientists in the UK. Prof Sir George Porter, on becoming President in September 1985, was scathing against so-called soft sciences such as psychology and he claimed this was damaging the public perception of science. We run the risk of doing neither well, universities are underfunded, and must not be seen simply as a substitute for National Service to keep youngsters off the dole queue. He also said scientists have to be careful and consider the implications of what they are seeking to achieve
24.
Orders of magnitude (power)
–
This page lists examples of the power in watts produced by various sources of energy. They are grouped by orders of magnitude, and each section covers three orders of magnitude, or a factor of one thousand,1.64 × 10−27 watt – phys, approximate power of gravitational radiation emitted by a 1000 kg satellite in geosynchronous orbit around the Earth. ~10 zW – tech, approximate power of Galileo space probes radio signal as received on earth by a 70-meter DSN antenna,1 aW – phys, approximate power scale at which operation of nanoelectromechanical systems are overwhelmed by thermal fluctuations. 100 aW – tech, the GPS signal strength measured at the surface of the Earth, for reference, about 10,000 100-watt lightbulbs or 5,000 computer systems would be needed to draw 1 MW. Also,1 MW is approximately 1360 horsepower, modern high-power diesel-electric locomotives typically have a peak power of 3–5 MW, while a typical modern nuclear power plant produces on the order of 500–2000 MW peak output. 8.21 GW – tech, capacity of the Kashiwazaki-Kariwa Nuclear Power Plant,73.1 GW - tech, total installed power capacity of Turkey on December 31,2015. 101.6 GW – tech, peak power consumption of France 166 GW – tech. 433 GW – tech, total installed wind turbine capacity at end of 2015,700 GW – biomed, humankind basal metabolic rate as of 2013. 2 TW – astro, approximate power generated between the surfaces of Jupiter and its moon Io due to Jupiters tremendous magnetic field,3.34 TW – geo, average total power consumption of the US in 200518. 1.1 PW – tech, worlds most powerful laser pulses by laser still in operation, ~2 X1.00 PW – tech, Omega EP laser power at the Laboratory for Laser Energetics. There are two beams that are combined. 1.25 PW – tech, worlds most powerful laser pulses,1.4 PW – geo, estimated heat flux transported by the Gulf Stream. 4 PW – geo, estimated heat flux transported by Earths atmosphere. 5.13 PW – tech, worlds most powerful laser pulses, 10–100 PW geo, estimated total power output of a Type-I civilization on the Kardashev scale. Barty also gave a talk on Laser-Based Nuclear Photonics at the SPIE meeting. 135 ZW – astro, approximate luminosity of Wolf 359 10-100 YW – geo, estimated total power output of a Type-II civilization on the Kardashev scale
25.
Orders of magnitude (numbers)
–
This list contains selected positive numbers in increasing order, including counts of things, dimensionless quantity and probabilities. Mathematics – Writing, Approximately 10−183,800 is a rough first estimate of the probability that a monkey, however, taking punctuation, capitalization, and spacing into account, the actual probability is far lower, around 10−360,783. Computing, The number 1×10−6176 is equal to the smallest positive non-zero value that can be represented by a quadruple-precision IEEE decimal floating-point value, Computing, The number 6. 5×10−4966 is approximately equal to the smallest positive non-zero value that can be represented by a quadruple-precision IEEE floating-point value. Computing, The number 3. 6×10−4951 is approximately equal to the smallest positive non-zero value that can be represented by a 80-bit x86 double-extended IEEE floating-point value. Computing, The number 1×10−398 is equal to the smallest positive non-zero value that can be represented by a double-precision IEEE decimal floating-point value, Computing, The number 4. 9×10−324 is approximately equal to the smallest positive non-zero value that can be represented by a double-precision IEEE floating-point value. Computing, The number 1×10−101 is equal to the smallest positive non-zero value that can be represented by a single-precision IEEE decimal floating-point value, Mathematics, The probability in a game of bridge of all four players getting a complete suit is approximately 4. 47×10−28. ISO, yocto- ISO, zepto- Mathematics, The probability of matching 20 numbers for 20 in a game of keno is approximately 2.83 × 10−19. ISO, atto- Mathematics, The probability of rolling snake eyes 10 times in a row on a pair of dice is about 2. 74×10−16. ISO, micro- Mathematics – Poker, The odds of being dealt a flush in poker are 649,739 to 1 against. Mathematics – Poker, The odds of being dealt a flush in poker are 72,192 to 1 against. Mathematics – Poker, The odds of being dealt a four of a kind in poker are 4,164 to 1 against, for a probability of 2.4 × 10−4. ISO, milli- Mathematics – Poker, The odds of being dealt a full house in poker are 693 to 1 against, for a probability of 1.4 × 10−3. Mathematics – Poker, The odds of being dealt a flush in poker are 507.8 to 1 against, Mathematics – Poker, The odds of being dealt a straight in poker are 253.8 to 1 against, for a probability of 4 × 10−3. Physics, α =0.007297352570, the fine-structure constant, ISO, deci- Mathematics – Poker, The odds of being dealt only one pair in poker are about 5 to 2 against, for a probability of 0.42. Demography, The population of Monowi, a village in Nebraska. Mathematics, √2 ≈1.414213562373095489, the ratio of the diagonal of a square to its side length. Mathematics, φ ≈1.618033988749895848, the golden ratio Mathematics, the number system understood by most computers, human scale, There are 10 digits on a pair of human hands, and 10 toes on a pair of human feet. Mathematics, The number system used in life, the decimal system, has 10 digits,0,1,2,3,4,5,6,7,8,9
26.
Radio
–
When radio waves strike an electrical conductor, the oscillating fields induce an alternating current in the conductor. The information in the waves can be extracted and transformed back into its original form, Radio systems need a transmitter to modulate some property of the energy produced to impress a signal on it, for example using amplitude modulation or angle modulation. Radio systems also need an antenna to convert electric currents into radio waves, an antenna can be used for both transmitting and receiving. The electrical resonance of tuned circuits in radios allow individual stations to be selected, the electromagnetic wave is intercepted by a tuned receiving antenna. Radio frequencies occupy the range from a 3 kHz to 300 GHz, a radio communication system sends signals by radio. The term radio is derived from the Latin word radius, meaning spoke of a wheel, beam of light, however, this invention would not be widely adopted. The switch to radio in place of wireless took place slowly and unevenly in the English-speaking world, the United States Navy would also play a role. Although its translation of the 1906 Berlin Convention used the terms wireless telegraph and wireless telegram, the term started to become preferred by the general public in the 1920s with the introduction of broadcasting. Radio systems used for communication have the following elements, with more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. Each system contains a transmitter, This consists of a source of electrical energy, the transmitter contains a system to modulate some property of the energy produced to impress a signal on it. This modulation might be as simple as turning the energy on and off, or altering more subtle such as amplitude, frequency, phase. Amplitude modulation of a carrier wave works by varying the strength of the signal in proportion to the information being sent. For example, changes in the strength can be used to reflect the sounds to be reproduced by a speaker. It was the used for the first audio radio transmissions. Frequency modulation varies the frequency of the carrier, the instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal. FM has the capture effect whereby a receiver only receives the strongest signal, Digital data can be sent by shifting the carriers frequency among a set of discrete values, a technique known as frequency-shift keying. FM is commonly used at Very high frequency radio frequencies for high-fidelity broadcasts of music, analog TV sound is also broadcast using FM. Angle modulation alters the phase of the carrier wave to transmit a signal
27.
Radar
–
Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the objects location and speed. Radar was developed secretly for military use by several nations in the period before, the term RADAR was coined in 1940 by the United States Navy as an acronym for RAdio Detection And Ranging or RAdio Direction And Ranging. The term radar has since entered English and other languages as a common noun, high tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels. Other systems similar to make use of other parts of the electromagnetic spectrum. One example is lidar, which uses ultraviolet, visible, or near infrared light from lasers rather than radio waves, as early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects. In 1895, Alexander Popov, an instructor at the Imperial Russian Navy school in Kronstadt. The next year, he added a spark-gap transmitter, in 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, the German inventor Christian Hülsmeyer was the first to use radio waves to detect the presence of distant metallic objects. In 1904, he demonstrated the feasibility of detecting a ship in dense fog and he obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23,1904 for a radar system. It operated on a 50 cm wavelength and the radar signal was created via a spark-gap. In 1915, Robert Watson-Watt used radio technology to advance warning to airmen. Watson-Watt became an expert on the use of direction finding as part of his lightning experiments. As part of ongoing experiments, he asked the new boy, Arnold Frederic Wilkins, Wilkins made an extensive study of available units before selecting a receiver model from the General Post Office. Its instruction manual noted that there was fading when aircraft flew by, in 1922, A. Hoyt Taylor and Leo C. Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, eight years later, Lawrence A. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war. Hugon, began developing a radio apparatus, a part of which was installed on the liner Normandie in 1935
28.
Decibel
–
The decibel is a logarithmic unit used to express the ratio of two values of a physical quantity. One of these values is often a reference value, in which case the decibel is used to express the level of the other value relative to this reference. When used in way, the decibel symbol is often qualified with a suffix that indicates the reference quantity that has been used or some other property of the quantity being measured. For example, dBm indicates a power of one milliwatt. There are two different scales used when expressing a ratio in decibels depending on the nature of the quantities, when expressing power quantities, the number of decibels is ten times the logarithm to base 10 of the ratio of two power quantities. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level, when expressing field quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The difference in scales relates to the square law of fields in three-dimensional linear space. The decibel scales differ so that comparisons can be made between related power and field quantities when they are expressed in decibels. The definition of the decibel is based on the measurement of power in telephony of the early 20th century in the Bell System in the United States. One decibel is one tenth of one bel, named in honor of Alexander Graham Bell, however, today, the decibel is used for a wide variety of measurements in science and engineering, most prominently in acoustics, electronics, and control theory. In electronics, the gains of amplifiers, attenuation of signals, the decibel originates from methods used to quantify signal loss in telegraph and telephone circuits. The unit for loss was originally Miles of Standard Cable, the standard telephone cable implied was a cable having uniformly distributed resistance of 88 ohms per loop mile and uniformly distributed shunt capacitance of 0.054 microfarad per mile. 1 TU was defined such that the number of TUs was ten times the logarithm of the ratio of measured power to a reference power level. The definition was conveniently chosen such that 1 TU approximated 1 MSC, in 1928, the Bell system renamed the TU into the decibel, being one tenth of a newly defined unit for the base-10 logarithm of the power ratio. It was named the bel, in honor of the telecommunications pioneer Alexander Graham Bell, the bel is seldom used, as the decibel was the proposed working unit. However, the decibel is recognized by international bodies such as the International Electrotechnical Commission. The term field quantity is deprecated by ISO 80000-1, which favors root-power, in spite of their widespread use, suffixes are not recognized by the IEC or ISO. The ISO Standard 80000-3,2006 defines the following quantities, the decibel is one-tenth of a bel,1 dB =0.1 B
29.
Radio astronomy
–
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The first detection of radio waves from an object was in 1932. Subsequent observations have identified a number of different sources of radio emission and these include stars and galaxies, as well as entirely new classes of objects, such as radio galaxies, quasars, pulsars, and masers. The discovery of the microwave background radiation, regarded as evidence for the Big Bang theory, was made through radio astronomy. Before Jansky observed the Milky Way in the 1930s, physicists speculated that radio waves could be observed from astronomical sources, in the 1860s, James Clerk Maxwells equations had shown that electromagnetic radiation is associated with electricity and magnetism, and could exist at any wavelength. These attempts were unable to detect any emission due to limitations of the instruments. The discovery of the radio reflecting ionosphere in 1902, led physicists to conclude that the layer would bounce any astronomical radio transmission back into space, Karl Jansky made the discovery of the first astronomical radio source serendipitously in the early 1930s. As an engineer with Bell Telephone Laboratories, he was investigating static that interfered with short wave transatlantic voice transmissions, using a large directional antenna, Jansky noticed that his analog pen-and-paper recording system kept recording a repeating signal of unknown origin. Since the signal peaked about every 24 hours, Jansky originally suspected the source of the interference was the Sun crossing the view of his directional antenna. Continued analysis showed that the source was not following the 24-hour daily cycle of the Sun exactly and he concluded that since the Sun were not large emitters of radio noise, the strange radio interference may be generated by interstellar gas and dust in the galaxy. Jansky announced his discovery in 1933 and he wanted to investigate the radio waves from the Milky Way in further detail, but Bell Labs reassigned him to another project, so he did no further work in the field of astronomy. His pioneering efforts in the field of astronomy have been recognized by the naming of the fundamental unit of flux density. Grote Reber was inspired by Janskys work, and built a radio telescope 9m in diameter in his backyard in 1937. He began by repeating Janskys observations, and then conducted the first sky survey in the radio frequencies, on February 27,1942, James Stanley Hey, a British Army research officer, made the first detection of radio waves emitted by the Sun. Later that year George Clark Southworth, at Bell Labs like Jansky, both researchers were bound by wartime security surrounding radar, so Reber, who was not, published his 1944 findings first. Several other people independently discovered solar radiowaves, including E. Schott in Denmark, at Cambridge University, where ionospheric research had taken place during World War II, J. A. This early research soon branched out into the observation of celestial radio sources. Martin Ryle and Antony Hewish at the Cavendish Astrophysics Group developed the technique of Earth-rotation aperture synthesis, the radio astronomy group in Cambridge went on to found the Mullard Radio Astronomy Observatory near Cambridge in the 1950s
30.
Sound power
–
Sound power or acoustic power is the rate at which sound energy is emitted, reflected, transmitted or received, per unit time. The SI unit of power is the watt. It is the power of the force on a surface of the medium of propagation of the sound wave. For a sound source, unlike sound pressure, sound power is neither room-dependent nor distance-dependent, Sound pressure is a measurement at a point in space near the source, while the sound power of a source is the total power emitted by that source in all directions. Sound power passing through an area is called sound flux or acoustic flux through that area. For example, a sound at SPL =85 dB or p =0.356 Pa in air through a surface of area A =1 m2 normal to the direction of propagation has an energy flux P =0.3 mW. This is the one would be interested in when converting noise back into usable energy. Here is a table of some examples, Sound power is related to sound intensity, P = A I, where A is the area, I is the sound intensity. Sound power is related sound energy density, P = A c w, Sound power level or acoustic power level is a logarithmic measure of the power of a sound relative to a reference value. The commonly used reference sound power in air is P0 =1 p W. The proper notations for sound power level using this reference are LW/ or LW, but the suffix notations dB SWL, dB, dBSWL, or dBSWL are very common, even if they are not accepted by the SI. The generic calculation of power from sound pressure is as follows, L W = L p +10 log 10 d B. This surface may be any shape, but it must fully enclose the source, derivation of this equation, L W =12 ln =12 ln =12 ln +12 ln. For a progressive spherical wave, z 0 = p v, A =4 π r 2, the sound power estimated practically does not depend on distance. The sound pressure used in the calculation may be affected by distance due to effects in the propagation of sound unless this is accounted for. Cause and Effect Ohms Law as Acoustic Equivalent, calculations Relationships of Acoustic Quantities Associated with a Plane Progressive Acoustic Sound Wave NIOSH Powertools Database Sound Power Testing
31.
Solar cell
–
A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance. Solar cells are the blocks of photovoltaic modules, otherwise known as solar panels. Solar cells are described as being photovoltaic, irrespective of whether the source is sunlight or an artificial light and they are used as a photodetector, detecting light or other electromagnetic radiation near the visible range, or measuring light intensity. The operation of a cell requires three basic attributes, The absorption of light, generating either electron-hole pairs or excitons. The separation of carriers of opposite types. The separate extraction of those carriers to an external circuit, in contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A photoelectrolytic cell, on the hand, refers either to a type of photovoltaic cell. Assemblies of solar cells are used to make solar modules that generate power from sunlight. A solar array generates power using solar energy. Multiple solar cells in a group, all oriented in one plane. Photovoltaic modules often have a sheet of glass on the sun-facing side, Solar cells are usually connected in series and parallel circuits or series in modules, creating an additive voltage. Strings of series cells are usually handled independently and not connected in parallel, though as of 2014, individual power boxes are often supplied for each module, and are connected in parallel. Although modules can be interconnected to create an array with the desired peak DC voltage and loading current capacity, otherwise, shunt diodes can reduce shadowing power loss in arrays with series/parallel connected cells. The photovoltaic effect was demonstrated first by French physicist Edmond Becquerel. In 1839, at age 19, he built the worlds first photovoltaic cell in his fathers laboratory, willoughby Smith first described the Effect of Light on Selenium during the passage of an Electric Current in a 20 February 1873 issue of Nature. In 1883 Charles Fritts built the first solid state photovoltaic cell by coating the semiconductor selenium with a layer of gold to form the junctions. In 1888 Russian physicist Aleksandr Stoletov built the first cell based on the photoelectric effect discovered by Heinrich Hertz in 1887
32.
Laser pointer
–
Power is restricted in most jurisdictions not to exceed 5 mW. The small width of the beam and low power of typical laser pointers make the beam itself invisible in a reasonably clean atmosphere, some higher-powered laser pointers project a visible beam via scattering from dust particles or water droplets along the beam path. The intensity of such scattering increases when these beams are viewed from angles near the beam axis, such pointers, particularly in the green-light output range, are used as astronomical-object pointers for teaching purposes. This invisible IR component causes a degree of potential hazard in these devices when pointed at nearby objects. If aimed at a persons eyes, laser pointers can cause temporary disturbances to vision, there is some evidence of rare minor permanent harm, but low-powered laser pointers are not seriously hazardous to health. They may be an annoyance in some circumstances. A dot of light from a red laser pointer may be thought to be due to a laser gunsight, when pointed at aircraft at night, laser pointers may dazzle and distract pilots, and increasingly strict laws have been passed to ban this. Early laser pointers were helium–neon gas lasers and generated laser radiation at 633 nanometers, the least expensive laser pointers use a deep-red laser diode near the 650 nm wavelength. Slightly more expensive ones use a red-orange 635 nm diode, more easily visible because of the sensitivity of the human eye at 635 nm. Other colors are too, with the 532 nm green laser being the most common alternative. Yellow-orange laser pointers, at 593.5 nm, later became available, in September 2005 handheld blue laser pointers at 473 nm became available. In early 2010 Blu-ray laser pointers at 405 nm went on sale, the apparent brightness of a spot from a laser beam depends on the optical power of the laser, the reflectivity of the surface, and the chromatic response of the human eye. For the same power, green laser light will seem brighter than other colors because the human eye is most sensitive at low light levels in the green region of the spectrum. Sensitivity decreases for longer and shorter wavelengths, the output power of a laser pointer is usually stated in milliwatts. In the U. S. lasers are classified by the American National Standards Institute and Food, visible laser pointers operating at less than 1 mW power are Class 2 or II, and visible laser pointers operating with 1–5 mW power are Class 3A or IIIa. Class 3B or IIIb lasers generate between 5 and 500 mW, Class 4 or IV lasers generate more than 500 mW. The US FDA Code of Federal Regulations stipulates that demonstration laser products such as pointers must comply with requirements for Class I, IIa, II. These are the simplest pointers, as laser diodes are available in these wavelengths, the pointer is nothing more than a battery-powered laser diode
33.
Hearing aid
–
A hearing aid or deaf aid is a device designed to improve hearing. Hearing aids are classified as medical devices in most countries, small audio amplifiers such as PSAPs or other plain sound reinforcing systems cannot be sold as hearing aids. Earlier devices, such as ear trumpets or ear horns, were passive amplification cones designed to gather sound energy, modern devices are computerised electroacoustic systems that transform environmental sound to make it more intelligible or comfortable, according to audiometrical and cognitive rules. Such sound processing can be considerable, such as highlighting a spatial region, shifting frequencies, cancelling noise and wind, modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. This process is called fitting and is performed by audiologists, the amount of benefit a hearing aid delivers depends in large part on the quality of its fitting. Devices similar to hearing aids include the bone anchored hearing aid, Hearing aids are incapable of truly correcting a hearing loss, they are an aid to make sounds more accessible. Two primary issues minimize the effectiveness of hearing aids, When the primary auditory cortex does not receive regular stimulation, cell loss increases as the degree of hearing loss increases. Damage to the cells of the inner ear results in sensorineural hearing loss. This often manifests as an ability to understand speech. Hearing aids are incapable of truly correcting a hearing loss, they are an aid to make more accessible. Three primary issues minimize the effectiveness of hearing aids, The occlusion effect is a common complaint, though if the aids are worn regularly, most people will become acclimated after a few weeks. If the effect persists, an audiologist or Hearing Instrument Specialist can sometimes further tune the hearing aid, the compression effect, The amplification needed to make quiet sounds audible, if applied to loud sounds would damage the inner ear. Louder sounds are therefore reduced giving a smaller audible volume range, Hearing protection is also provided by an overall cap to the sound pressure. Also of protective value is impulse noise suppression, available in some high-end aids, the initial fitting appointment is rarely sufficient, and multiple follow-up visits are often necessary. Most audiologists or Hearing Instrument Specialists will recommend an up-to-date audiogram at the time of purchase, there are several ways of evaluating how well a hearing aid compensates for hearing loss. One approach is audiometry which measures a subjects hearing levels in laboratory conditions, the threshold of audibility for various sounds and intensities is measured in a variety of conditions. Although audiometric tests may attempt to mimic real-world conditions, the patients own every day experiences may differ, an alternative approach is self-report assessment, where the patient reports their experience with the hearing aid. Real ear measurements are an assessment of the characteristics of hearing aid amplification near the ear drum using a silicone probe tube microphone, there are many types of hearing aids, which vary in size, power and circuitry
34.
DBm
–
DBm is an abbreviation for the power ratio in decibels of the measured power referenced to one milliwatt. It is used in radio, microwave and fiber-optical networks as a convenient measure of power because of its capability to express both very large and very small values in a short form. Compare dBW, which is referenced to one watt, since it is referenced to the watt, it is an absolute unit, used when measuring absolute power. By comparison, the decibel is a unit, used for quantifying the ratio between two values, such as signal-to-noise ratio. In audio and telephony, dBm is typically referenced relative to a 600-ohm impedance, a power level of 0 dBm corresponds to a power of 1 milliwatt. A10 dB increase in level is equivalent to 10 times the power, a 3 dB increase in level is approximately equivalent to doubling the power, which means that a level of 3 dBm corresponds roughly to a power of 2 mW. For each 3 dB decrease in level, the power is reduced by one half. In United States Department of Defense practice, unweighted measurement is normally understood, applicable to a certain bandwidth, in European practice, psophometric weighting may be, as indicated by context, equivalent to dBm0p, which is preferred. In audio,0 dBm often corresponds to approximately 0.775 volts, dBu measures against this reference voltage without the 600 Ω restriction. Conversely, for RF situations with a 50 Ω load,0 dBm corresponds to approximately 0.224 volts, the dBm is not a part of the International System of Units and therefore is discouraged from use in documents or systems that adhere to SI units. However, the decibel, being a unitless ratio of two numbers, is perfectly acceptable. Expression in dBm is typically used for optical and electrical power measurements, a listing by power levels in watts is available that includes a variety of examples not necessarily related to electrical or optical power. The dBm was first proposed as a standard in the paper A New Standard Volume Indicator. DBW Decibel This article incorporates public domain material from the General Services Administration document Federal Standard 1037C, the dBm calculator for impedance matching Convert dBm to watts