Joule effect and Joule's law are any of several different physical effects discovered or characterized by English physicist

James Prescott Joule James Prescott Joule (; 24 December 1818 11 October 1889) was an English physicist, mathematician and brewer, born in Salford, Lancashire. Joule studied the nature of heat, and discovered its relationship to mechanical work (see energy). Th ...

. These physical effects are not the same, but all are frequently or occasionally referred to in the literature as the "Joule effect" or "Joule law" These physical effects include: * "

Joule's first law Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law (also just Joule's law), also known in countries of former US ...

" (Joule heating), a physical law expressing the relationship between the heat generated and the current flowing through a conductor. * Joule's second law states that the

internal energy The internal energy of a thermodynamic system is the total energy contained within it. It is the energy necessary to create or prepare the system in its given internal state, and includes the contributions of potential energy and internal kinet ...

of an

ideal gas An ideal gas is a theoretical gas composed of many randomly moving point particles that are not subject to interparticle interactions. The ideal gas concept is useful because it obeys the ideal gas law, a simplified equation of state, and is a ...

is independent of its volume and pressure, depending only on its temperature. *

Magnetostriction Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field change ...

, a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. * The

Joule–Thomson effect In thermodynamics, the Joule–Thomson effect (also known as the Joule–Kelvin effect or Kelvin–Joule effect) describes the temperature change of a ''real'' gas or liquid (as differentiated from an ideal gas) when it is forced through a valv ...

(during

Joule expansion The Joule expansion (also called free expansion) is an irreversible process in thermodynamics in which a volume of gas is kept in one side of a thermally isolated container (via a small partition), with the other side of the container being evacu ...

), the temperature change of a gas (usually cooling) when it is allowed to expand freely. * The

Gough–Joule effect The Gough–Joule effect (a.k.a. Gow–Joule effect) is originally the tendency of elastomers to contract when heated if they are under tension. Elastomers that are not under tension do not see this effect. The term is also used more generally to re ...

or the Gow–Joule effect, which is the tendency of

elastomer An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...

s to contract if heated while they are under tension.

Joule's first law

Between 1840 and 1843, Joule carefully studied the heat produced by an electric current. From this study, he developed Joule's laws of heating, the first of which is commonly referred to as the ''Joule effect''. Joule's first law expresses the relationship between heat generated in a conductor and current flow, resistance, and time.

Magnetostriction

The

magnetostriction Magnetostriction (cf. electrostriction) is a property of magnetic materials that causes them to change their shape or dimensions during the process of magnetization. The variation of materials' magnetization due to the applied magnetic field change ...

effect describes a property of ferromagnetic materials which causes them to change their shape when subjected to a magnetic field. Joule first reported observing the change in the length of ferromagnetic rods in 1842.

Joule expansion

In 1845, Joule studied the free expansion of a gas into a larger volume. This became known as

. The cooling of a gas by allowing it to expand freely is occasionally referred to as the Joule effect.

Gough–Joule effect

If an elastic band is first stretched and then subjected to heating, it will shrink rather than expand. This effect was first observed by John Gough in 1802, and was investigated further by Joule in the 1850s, when it then became known as the

.
''Examples in Literature:'' * Popular Science magazine, January 1972: "A stretched piece of rubber ''contracts'' when heated. In doing so, it exerts a measurable increase in its pull. This surprising property of rubber was first observed by James Prescott Joule about a hundred years ago and is known as the Joule effect." * Rubber as an Engineering Material (book), by Khairi Nagdi: "The Joule effect is a phenomenon of practical importance that machine designers must consider. The simplest way of demonstrating this effect is to suspend a weight on a rubber band sufficient to elongate it by at least 50%. When an infrared lamp warms up the stretched rubber band, it does not elongate because of thermal expansion, as may be expected, but it retracts and lifts the weight."

References

{{reflist Thermodynamics

Joule's first law

Magnetostriction

Joule expansion

Gough–Joule effect

See also

References