The volt is the derived unit for electric potential, electric potential difference, electromotive force. It is named after the Italian physicist Alessandro Volta. One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. Additionally, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it, it can be expressed in terms of SI base units as: V = potential energy charge = J C = kg ⋅ m 2 A ⋅ s 3. It can be expressed as amperes times ohms, webers per second, watts per ampere, or joules per coulomb, equivalent to electronvolts per elementary charge: V = A ⋅ Ω = Wb s = W A = J C = eV e; the "conventional" volt, V90, defined in 1987 by the 18th General Conference on Weights and Measures and in use from 1990, is implemented using the Josephson effect for exact frequency-to-voltage conversion, combined with the caesium frequency standard.

For the Josephson constant, KJ = 2e/h, a "conventional" value KJ-90 = 0.4835979 GHz/μV was used for the purpose of defining the volt. As a consequence of the 2019 redefinition of SI base units, the Josephson constant was redefined in 2019 to have an exact value of KJ = 483597.84841698... GHz⋅V−1, which replaced the conventional value KJ-90; this standard is realized using a series-connected array of several thousand or tens of thousands of junctions, excited by microwave signals between 10 and 80 GHz. Empirically, several experiments have shown that the method is independent of device design, measurement setup, etc. and no correction terms are required in a practical implementation. 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 amount of water flowing at that pressure. A resistor would be a reduced diameter somewhere in the piping and a capacitor/inductor could be likened to a "U" shaped pipe where a higher water level on one side could store energy temporarily.

The relationship between voltage and current is defined by Ohm's law. Ohm's 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, or additional circuitry added to adjust the voltage to a different level. Mechanical generators can be constructed to any voltage in a range of feasibility. Nominal voltages of familiar sources: Nerve cell resting potential: ~75 mV Single-cell, rechargeable NiMH or NiCd battery: 1.2 V Single-cell, non-rechargeable: alkaline battery: 1.5 V. The charging system voltage regulator adjustment and resulting current flow required to power all vehicle loads and "isolate" the storage battery from those loads and maintain the battery at a full state of charge by overcoming its internal resistance is 14.4 volts. Because of its internal resistance and its use to measure the "voltage drop" across "loads" in a powered closed circuit, until a multimeter is "testing" the "voltage drop" across a battery in a "closed circuit", it is not measuring "battery voltage".

Only unpowered "analog" voltmeters provide a true reading of "voltage" as they complete a circuit and current flows through them and since voltage is a function of current flow and resistance, a charging "12-volt" electrical system is not affected by "voltage drop" and "charging system voltage" will be present at all "positive terminals" throughout the vehicle accessory circuits. When a "discharging" battery only is powering the same circuits, voltage drops increase as "positive terminals" are separated from the battery by increased resistance; because automotive batteries are never used to supply "continous loads" in a "total loss" situation, they are not analogous to "rechargeable" dry-cell batteries which are the sole sourc

All-Time Greatest Hits is a 3 disc compilation album issued in 1993 by CEMA Special Markets, containing single A-sides released between 1966 and 1978. This album is notable because of the presence of several single-only releases that have not been available on CD: "Oklahoma Sunday Morning", "Manhattan Kansas", "Wherefore and Why" and "God Must Have Blessed America". Disc 1: "Rhinestone Cowboy" "By The Time I Get To Phoenix" "It's Only Make Believe" "Burning Bridges" "I Wanna Live" "I'm Gonna Love You" "Southern Nights" "Houston" "Try A Little Kindness" "Where's The Playground Susie" "Hey Little One" "Manhattan Kansas" Disc 2: "Gentle On My Mind" "Dream Baby" "True Grit" "Oh Happy Day" "Sunflower" "It's A Sin When You Love Somebody" "Country Boy" "Wichita Lineman" "All I Have To Do Is Dream" "Galveston" "Everything A Man Could Ever Need" "Oklahoma Sunday Morning" Disc 3: "Honey Come Back" "Dreams of the Everyday Housewife" "The Last Time I Saw Her" "Don't Pull Your Love/Then You Can Tell Me Goodbye" "See You On Sunday" "Let It Be Me" "Bonaparte's Retreat" "Wherefore And Why" "I Will Never Pass This Way Again" "God Must Have Blessed America" "Can You Fool" Package design by Jerry Wiant Design Manufactured in Canada

The elm cultivar Ulmus'Purpurea', the purple-leaved elm, was listed and described as Ulmus Stricta Purpurea, the'Upright Purpled-leaved Elm', by John Frederick Wood, F. H. S. in The Midland Florist and Suburban Horticulturist, as Ulmus purpurea Hort. by Wesmael, as Ulmus campestris var. purpurea, syn. Ulmus purpurea Hort. by Petzold and Kirchner in Arboretum Muscaviense. Koch's description followed. Henry noted that the Ulmus campestris var. purpurea Petz. & Kirchn. Grown at Kew as U. montana var. purpurea was "probably of hybrid origin", Ulmus montana being used at the time both for wych elm cultivars and for some of the U. × hollandica group. His description of Kew's U. montana var. purpurea matches that of the commonly-planted'Purpurea' of the 20th century. His discussion of it under U. campestris, his name for English Elm, may be the reason why'Purpurea' is sometimes erroneously called U. procera'Purpurea' (as in USA and Sweden. The fact that'Purpurea' produces root-suckers confirms a hybrid origin with some U. minor component.

F. J. Fontaine conjectured U. glabra × U. minor'Stricta' and placed the tree in the U. × hollandica group under the name U. × hollandica'Purpurascens', a name accepted by Royal Botanic Gardens Edinburgh and in Australian publications. The samarae and the habit of'Purpurea' appear to support this conjecture. See also'Atropurpurea' synonymous, raised by the Späth nursery in Berlin c.1881 and sometimes classed as a wych cultivar. Wych elm itself produces red- or purple-flushed new leaves, the 19th century variety'Corylifolia Purpurea' being an example. There is a small-leaved elm U. minor'Purpurascens', which nurseries listed and distributed separately from U. campestris purpurea Hort.. In North America, purple-leaved elms encountered in the fall are to be the new hybrid Ulmus'Frontier'. Of Ulmus Stricta Purpurea Wood wrote: "When young, the foliage is dark purple, in the way of the Purple Beech; as the season advances, it becomes somewhat greener, but always retains a distinct and peculiar character."

The leaves of Wesmael's Ulmus purpurea Hort. were a "characteristic bronzy green". Those of Petzold and Kirchner's Ulmus campestris var. purpurea, syn. Ulmus purpurea Hort. "emerged dark purple becoming more green, but always of a dark, reddish-green, peculiar". Koch's U. purpurea had "leaves purple when young, changing to dark green".'Purpurea' grows to > 25 m in height, is short-trunked with open, ascending branches. The leaf-buds are long pointed and dark purple, on shoots of the same colour; the flowers, emerge a uniform dark purple. The fruit, tinged purple over the seed, is U. minor. The leaves, which are folded, have a brief purplish-green flush in spring; the new leaves of lower bole-shoots and of suckers are pure dark purple, without any green. After the spring flush, the leaves become olive green darken in the summer, their underside is paler, so that, with their increasing fold as the year progresses, the late-summer foliage has a greyish look. The bark of younger trees has a reddish-brown hue.

The tree is susceptible to Dutch elm disease.'Purpurea' Hort. was in cultivation in Europe from the 1860s. U. × hollandica'Purpurascens' was "produced in quantity" by nurseries in Oudenbosch, the Netherlands. It is still present in Sweden, but appears to have been rarer in cultivation in the UK. In 2007 the Swedish Biodiversity Centre's'Programme for Diversity of Cultivated Plants' included'Purpurascens' in their plant conservation programme. Introduced to the USA in the late 1860s as Ulmus stricta purpurea,'Purple leaved elm' was stocked by the Mount Hope Nursery of Rochester, New York. An U. campestris purpurea,'Purple-leaved English Elm', of "compact upright growth" with "leaves a purple color in May and June", appeared in the 1902 catalogue of the Bobbink and Atkins nursery, New Jersey, an U. stricta purpurea called'Purple-leaved English Elm', "a tree with erect branches and purplish-red leaves", in both Bobbink and Atkins' 1902 catalogue and Kelsey's 1904 catalogue, New York. An elm obtained in 1922 from H. Kohankie & Son is listed by the Morton Arboretum, Illinois, as Ulmus procera'Purpurea', but without description.

In arboretum photographs its bark and form do not appear to resemble hybrid'Purpurea'. In Australia cultivars by the name of U. glabra Huds.'Purpurea', U. procera'Purpurea' and U. purpurea appear in nursery catalogues dating from 1882. Urban plantings include avenue specimens and scattered trees in Fawkner Park, Melbourne.. A large specimen stands in Edinburgh. Six of the seven mature specimens growing there were felled in the 1990s. A vigorous sucker in the cemetery has now become an establishe