Electrical engineering is a professional engineering discipline that deals with the study and application of electricity and electromagnetism. This field first became an identifiable occupation in the half of the 19th century after commercialization of the electric telegraph, the telephone, electric power distribution and use. Subsequently and recording media made electronics part of daily life; the invention of the transistor, the integrated circuit, brought down the cost of electronics to the point they can be used in any household object. Electrical engineering has now divided into a wide range of fields including electronics, digital computers, computer engineering, power engineering, telecommunications, control systems, radio-frequency engineering, signal processing and microelectronics. Many of these disciplines overlap with other engineering branches, spanning a huge number of specializations such as hardware engineering, power electronics and waves, microwave engineering, electrochemistry, renewable energies, electrical materials science, much more.
See glossary of electrical and electronics engineering. Electrical engineers hold a degree in electrical engineering or electronic engineering. Practising engineers may be members of a professional body; such bodies include the Institute of Electrical and Electronics Engineers and the Institution of Engineering and Technology. Electrical engineers work in a wide range of industries and the skills required are variable; these range from basic circuit theory to the management skills required of a project manager. The tools and equipment that an individual engineer may need are variable, ranging from a simple voltmeter to a top end analyzer to sophisticated design and manufacturing software. Electricity has been a subject of scientific interest since at least the early 17th century. William Gilbert was a prominent early electrical scientist, was the first to draw a clear distinction between magnetism and static electricity, he is credited with establishing the term "electricity". He designed the versorium: a device that detects the presence of statically charged objects.
In 1762 Swedish professor Johan Carl Wilcke invented a device named electrophorus that produced a static electric charge. By 1800 Alessandro Volta had developed the voltaic pile, a forerunner of the electric battery In the 19th century, research into the subject started to intensify. Notable developments in this century include the work of Hans Christian Ørsted who discovered in 1820 that an electric current produces a magnetic field that will deflect a compass needle, of William Sturgeon who, in 1825 invented the electromagnet, of Joseph Henry and Edward Davy who invented the electrical relay in 1835, of Georg Ohm, who in 1827 quantified the relationship between the electric current and potential difference in a conductor, of Michael Faraday, of James Clerk Maxwell, who in 1873 published a unified theory of electricity and magnetism in his treatise Electricity and Magnetism. In 1782 Georges-Louis Le Sage developed and presented in Berlin the world's first form of electric telegraphy, using 24 different wires, one for each letter of the alphabet.
This telegraph connected two rooms. It was an electrostatic telegraph. In 1795, Francisco Salva Campillo proposed an electrostatic telegraph system. Between 1803-1804, he worked on electrical telegraphy and in 1804, he presented his report at the Royal Academy of Natural Sciences and Arts of Barcelona. Salva’s electrolyte telegraph system was innovative though it was influenced by and based upon two new discoveries made in Europe in 1800 – Alessandro Volta’s electric battery for generating an electric current and William Nicholson and Anthony Carlyle’s electrolysis of water. Electrical telegraphy may be considered the first example of electrical engineering. Electrical engineering became a profession in the 19th century. Practitioners had created a global electric telegraph network and the first professional electrical engineering institutions were founded in the UK and USA to support the new discipline. Francis Ronalds created an electric telegraph system in 1816 and documented his vision of how the world could be transformed by electricity.
Over 50 years he joined the new Society of Telegraph Engineers where he was regarded by other members as the first of their cohort. By the end of the 19th century, the world had been forever changed by the rapid communication made possible by the engineering development of land-lines, submarine cables, from about 1890, wireless telegraphy. Practical applications and advances in such fields created an increasing need for standardised units of measure, they led to the international standardization of the units volt, coulomb, ohm and henry. This was achieved at an international conference in Chicago in 1893; the publication of these standards formed the basis of future advances in standardisation in various industries, in many countries, the definitions were recognized in relevant legislation. During these years, the study of electricity was considered to be a subfield of physics since the early electrical technology was considered electromechanical in nature; the Technische Universität Darmstadt founded the world's first department of electrical engineering in 1882.
The first electrical engineering degree program was started at Massachusetts Institute of Technology in the physics department
An LC circuit called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, a capacitor, represented by the letter C, connected together. The circuit can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuit's resonant frequency. LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal, they are key components in many electronic devices radio equipment, used in circuits such as oscillators, filters and frequency mixers. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance. Any practical implementation of an LC circuit will always include loss resulting from small but non-zero resistance within the components and connecting wires; the purpose of an LC circuit is to oscillate with minimal damping, so the resistance is made as low as possible.
While no practical circuit is without losses, it is nonetheless instructive to study this ideal form of the circuit to gain understanding and physical intuition. For a circuit model incorporating resistance, see RLC circuit; the two-element LC circuit described above is the simplest type of inductor-capacitor network. It is referred to as a second order LC circuit to distinguish it from more complicated LC networks with more inductors and capacitors; such LC networks with more than two reactances may have more than one resonant frequency. The order of the network is the order of the rational function describing the network in the complex frequency variable s; the order is equal to the number of L and C elements in the circuit and in any event cannot exceed this number. An LC circuit, oscillating at its natural resonant frequency, can store electrical energy. See the animation. A capacitor stores energy in the electric field between its plates, depending on the voltage across it, an inductor stores energy in its magnetic field, depending on the current through it.
If an inductor is connected across a charged capacitor, current will start to flow through the inductor, building up a magnetic field around it and reducing the voltage on the capacitor. All the charge on the capacitor will be gone and the voltage across it will reach zero. However, the current will continue; the current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday's law, the EMF which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field; when the magnetic field is dissipated the current will stop and the charge will again be stored in the capacitor, with the opposite polarity as before. The cycle will begin again, with the current flowing in the opposite direction through the inductor; the charge flows back and forth through the inductor. The energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out.
The tuned circuit's action, known mathematically as a harmonic oscillator, is similar to a pendulum swinging back and forth, or water sloshing back and forth in a tank. The natural frequency is determined by the inductance values. In most applications the tuned circuit is part of a larger circuit which applies alternating current to it, driving continuous oscillations. If the frequency of the applied current is the circuit's natural resonant frequency, resonance will occur, a small driving current can excite large amplitude oscillating voltages and currents. In typical tuned circuits in electronic equipment the oscillations are fast, from thousands to billions of times per second. Resonance occurs when an LC circuit is driven from an external source at an angular frequency ω0 at which the inductive and capacitive reactances are equal in magnitude; the frequency at which this equality holds for the particular circuit is called the resonant frequency. The resonant frequency of the LC circuit is ω 0 = 1 L C where L is the inductance in henrys, C is the capacitance in farads.
The angular frequency ω0 has units of radians per second. The equivalent frequency in units of hertz is f 0 = ω 0 2 π = 1 2 π L C; the resonance effect of the LC circuit has many important applications in signal processing and communications systems. The most common application of tank circuits is tuning radio receivers. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency. A series resonant circuit provides voltage magnification. A parallel resonant circuit provides current magnification. A parallel resonant circuit can be used as load impedance in output circuits of RF amplifiers. Due to high impedance, the gain of amplifier is maximum at resonant frequency
Alternating current is an electric current which periodically reverses direction, in contrast to direct current which flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, it is the form of electrical energy that consumers use when they plug kitchen appliances, televisions and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight; the abbreviations AC and DC are used to mean alternating and direct, as when they modify current or voltage. The usual waveform of alternating current in most electric power circuits is a sine wave, whose positive half-period corresponds with positive direction of the current and vice versa. In certain applications, different waveforms are used, such as square waves. Audio and radio signals carried on electrical wires are examples of alternating current; these types of alternating current carry information such as sound or images sometimes carried by modulation of an AC carrier signal.
These currents alternate at higher frequencies than those used in power transmission. Electrical energy is distributed as alternating current because AC voltage may be increased or decreased with a transformer; this allows the power to be transmitted through power lines efficiently at high voltage, which reduces the energy lost as heat due to resistance of the wire, transformed to a lower, voltage for use. Use of a higher voltage leads to more efficient transmission of power; the power losses in the wire are a product of the square of the current and the resistance of the wire, described by the formula: P w = I 2 R. This means that when transmitting a fixed power on a given wire, if the current is halved, the power loss due to the wire's resistance will be reduced to one quarter; the power transmitted is equal to the product of the voltage. Power is transmitted at hundreds of kilovolts, transformed to 100 V – 240 V for domestic use. High voltages have disadvantages, such as the increased insulation required, increased difficulty in their safe handling.
In a power plant, energy is generated at a convenient voltage for the design of a generator, stepped up to a high voltage for transmission. Near the loads, the transmission voltage is stepped down to the voltages used by equipment. Consumer voltages vary somewhat depending on the country and size of load, but motors and lighting are built to use up to a few hundred volts between phases; the voltage delivered to equipment such as lighting and motor loads is standardized, with an allowable range of voltage over which equipment is expected to operate. Standard power utilization voltages and percentage tolerance vary in the different mains power systems found in the world. High-voltage direct-current electric power transmission systems have become more viable as technology has provided efficient means of changing the voltage of DC power. Transmission with high voltage direct current was not feasible in the early days of electric power transmission, as there was no economically viable way to step down the voltage of DC for end user applications such as lighting incandescent bulbs.
Three-phase electrical generation is common. The simplest way is to use three separate coils in the generator stator, physically offset by an angle of 120° to each other. Three current waveforms are produced that are equal in magnitude and 120° out of phase to each other. If coils are added opposite to these, they generate the same phases with reverse polarity and so can be wired together. In practice, higher "pole orders" are used. For example, a 12-pole machine would have 36 coils; the advantage is. For example, a 2-pole machine running at 3600 rpm and a 12-pole machine running at 600 rpm produce the same frequency. If the load on a three-phase system is balanced among the phases, no current flows through the neutral point. In the worst-case unbalanced load, the neutral current will not exceed the highest of the phase currents. Non-linear loads may require an oversized neutral bus and neutral conductor in the upstream distribution panel to handle harmonics. Harmonics can cause neutral conductor current levels to exceed that of all phase conductors.
For three-phase at utilization voltages a four-wire system is used. When stepping down three-phase, a transformer with a Delta primary and a Star secondary is used so there is no need for a neutral on the supply side. For smaller customers only a single phase and neutral, or two phases and neutral, are taken to the property. For larger installations all three phases and neutral are taken to the main distribution panel. From the three-phase main panel, both single and three-phase circuits may lead off. Three-wire single-phase systems, with a single center-tapped transformer giving two live conductors, is a common distribution scheme for res
A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a low electrical impedance. This results in an excessive amount of current flowing into the circuit; the electrical opposite of a short circuit is an "open circuit", an infinite resistance between two nodes. It is common to misuse "short circuit" to describe any electrical malfunction, regardless of the actual problem. A short circuit is an abnormal connection between two nodes of an electric circuit intended to be at different voltages; this results in an electric current limited only by the Thévenin equivalent resistance of the rest of the network which can cause circuit damage, fire or explosion. Although the result of a fault, there are cases where short circuits are caused intentionally, for example, for the purpose of voltage-sensing crowbar circuit protectors. In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same voltage.
In an'ideal' short circuit, this means there is no resistance and thus no voltage drop across the connection. In real circuits, the result is a connection with no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit. A common type of short circuit occurs when the positive and negative terminals of a battery are connected with a low-resistance conductor, like a wire. With a low resistance in the connection, a high current will flow, causing the delivery of a large amount of energy in a short period of time. A high current flowing through a battery can cause a rapid increase of temperature resulting in an explosion with the release of hydrogen gas and electrolyte, which can burn tissue and cause blindness or death. Overloaded wires will overheat causing damage to the wire's insulation, or starting a fire. High current conditions may occur with electric motor loads under stalled conditions, such as when the impeller of an electrically driven pump is jammed by debris.
In electrical devices unintentional short circuits are caused when a wire's insulation breaks down, or when another conducting material is introduced, allowing charge to flow along a different path than the one intended. In mains circuits, short circuits may occur between two phases, between a phase and neutral or between a phase and earth; such short circuits are to result in a high current and therefore trigger an overcurrent protection device. However, it is possible for short circuits to arise between neutral and earth conductors, between two conductors of the same phase; such short circuits can be dangerous as they may not result in a large current and are therefore less to be detected. Possible effects include unexpected energisation of a circuit presumed to be isolated. To help reduce the negative effects of short circuits, power distribution transformers are deliberately designed to have a certain amount of leakage reactance; the leakage reactance helps the magnitude and rate of rise of the fault current.
A short circuit may lead to formation of an electric arc. The arc, a channel of hot ionized plasma, is conductive and can persist after significant amounts of original material from the conductors has evaporated. Surface erosion is a typical sign of electric arc damage. Short arcs can remove significant amounts of material from the electrodes; the temperature of the resulting electrical arc is high, causing the metal on the contact surfaces to melt and migrate with the current, as well as to escape into the air as fine particulate matter. A short circuit fault current can, within milliseconds, be thousands of times larger than the normal operating current of the system. Damage from short circuits can be reduced or prevented by employing fuses, circuit breakers, or other overload protection, which disconnect the power in reaction to excessive current. Overload protection must be chosen according to the current rating of the circuit. Circuits for large home appliances require protective devices set or rated for higher currents than lighting circuits.
Wire gauges specified in building and electrical codes are chosen to ensure safe operation in conjunction with the overload protection. An overcurrent protection device must be rated to safely interrupt the maximum prospective short-circuit current. In an improper installation, the overcurrent from a short circuit may cause ohmic heating of the circuit parts with poor conductivity; such overheating is a common cause of fires. An electric arc, if it forms during the short circuit, produces high amount of heat and can cause ignition of combustible substances as well. In industrial and utility distribution systems, dynamic forces generated by high short-circuit currents cause conductors to spread apart. Busbars and apparatus can be damaged by the forces generated in a short circuit. In electronics, the ideal model of an operational amplifier is said to produce a virtual short circuit between its input terminals because no matter what the output voltage is, the difference of potential between its input terminals is zero.
If one of the input terminals is connected to the ground the other one is said to provide a virtual ground because its potential is identical to that of the ground. An ideal operational amplifier has infinite input impedance, so unlike a real short circuit, no current flows b
Radio is the technology of signalling or communicating using radio waves. Radio waves are electromagnetic waves of frequency between 300 gigahertz, they are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, received by a radio receiver connected to another antenna. Radio is widely used in modern technology, in radio communication, radio navigation, remote control, remote sensing and other applications. In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking and satellite communication among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal in the transmitter. In radar, used to locate and track objects like aircraft, ships and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, the reflected waves reveal the object's location. In radio navigation systems such as GPS and VOR, a mobile receiver receives radio signals from navigational radio beacons whose position is known, by measuring the arrival time of the radio waves the receiver can calculate its position on Earth.
In wireless remote control devices like drones, garage door openers, keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device. Applications of radio waves which do not involve transmitting the waves significant distances, such as RF heating used in industrial processes and microwave ovens, medical uses such as diathermy and MRI machines, are not called radio; the noun radio is used to mean a broadcast radio receiver. Radio waves were first identified and studied by German physicist Heinrich Hertz in 1886; the first practical radio transmitters and receivers were developed around 1895-6 by Italian Guglielmo Marconi, radio began to be used commercially around 1900. To prevent interference between users, the emission of radio waves is regulated by law, coordinated by an international body called the International Telecommunications Union, which allocates frequency bands in the radio spectrum for different uses. Radio waves are radiated by electric charges undergoing acceleration.
They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna. In transmission, a transmitter generates an alternating current of radio frequency, applied to an antenna; the antenna radiates the power in the current as radio waves. When the waves strike the antenna of a radio receiver, they push the electrons in the metal back and forth, inducing a tiny alternating current; the radio receiver connected to the receiving antenna detects this oscillating current and amplifies it. As they travel further from the transmitting antenna, radio waves spread out so their signal strength decreases, so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, antenna radiation pattern, receiver sensitivity, noise level, presence of obstructions between transmitter and receiver. An omnidirectional antenna transmits or receives radio waves in all directions, while a directional antenna or high gain antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction.
Radio waves travel through a vacuum at the speed of light, in air at close to the speed of light, so the wavelength of a radio wave, the distance in meters between adjacent crests of the wave, is inversely proportional to its frequency. In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal; the modulation signal may be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter. In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency, called the carrier wave because it serves to "carry" the information through the air; the information signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information on the carrier.
Different radio systems use different modulation methods: AM - in an AM transmitter, the amplitude of the radio carrier wave is varied by the modulation signal. FM - in an FM transmitter, the frequency of the radio carrier wave is varied by the modulation signal. FSK - used in wireless digital devices to transmit digital signals, the frequency of the carrier wave is shifted periodically between two frequencies that represent the two binary digits, 0 and 1, to transmit a sequence of bits. OFDM - a family of complicated digital modulation methods widely used in high bandwidth systems such as WiFi networks, digital television broadcasting, digital audio broadcasting to transmit digital data using a minimum of radio spectrum bandwidth. OFDM has higher spectral efficiency and more resistance to fading than AM or FM. Multiple radio carrier waves spaced in frequency are transmitted within the radio channel, with each carrier modulated with bits from the incoming bitstream
Moritz von Jacobi
Moritz Hermann von Jacobi was a German and Russian engineer and physicist born in Potsdam. Jacobi worked in Russia, he furthered progress in galvanoplastics, electric motors, wire telegraphy. In 1834 he began to study magnetic motors. In 1835 moved to Dorpat to lecture at Dorpat University, he moved to Saint Petersburg in 1837 to research usage of electromagnetic forces for moving machines for Russian Academy of Sciences. He investigated the power of an electromagnet in generators. While studying the transfer of power from a battery to an electric motor, he deduced the maximum power theorem. Jacobi tested motors output by determining the amount of zinc consumed by the battery. With financial assistance of Czar Nicholas, Jacobi constructed in 1839 a 28-foot electric motor boat powered by battery cells; the boat carried 14 passengers on the Neva river against the current. The boat travelled at three miles per hour; the law known as the maximum power theorem states: "Maximum power is transferred when the internal resistance of the source equals the resistance of the load, when the external resistance can be varied, the internal resistance is constant."The transfer of maximum power from a source with a fixed internal resistance to a load, the resistance of the load must be the same as that of the source.
This law is of use. Jacobi obtained his theorem by applying common sense. In 1838, he discovered galvanoplastics, or electrotyping, a method of making printing plates by electroplating; the way in which this works is analogous to a battery acting in reverse. The stereotype was an impression taken from a form of movable lead type and used for printing instead of the original type; this technique is used in relief printing. He worked on the development of the electric telegraph. In 1842-1845 he built a telegraph line between Saint Petersburg and Tsarskoe Selo using an underground cable. In 1867 he was a Russian delegate to the Commission on measurement units at the Paris World's Fair, he was a strong proponent of the metric system. In 1853, Jacobi developed the Jacobi naval mine; the mine was tied to the sea bottom by an anchor, a cable connected it to a galvanic cell which powered it from the shore, the power of its explosive charge was equal to 14 kilograms of black powder. Its production was approved by the Committee for Mines of the Ministry of War of the Russian Empire and in 1854 60 Jacobi mines were laid in the vicinity of the Forts Pavel and Alexander.
His family was Jewish. He was a brother of the mathematician Carl Gustav Jacob Jacobi. Katz, Eugenii. "Moritz Hermann Jacobi". Archived from the original on 2006-10-06. Calvert, J. B. "Jacobi's Theorem Also known as the Maximum Power Transfer Theorem, misunderstanding of it retarded development of dynamos". March 30, 2001 Jacobi's motor - The first real electric motor of 1834