Related topics: magnetic field · superconductors

How do electrons behave in quantum critical ferromagnets?

In a classical second-order phase transition, condensed matter systems acquire long-range order upon cooling below the transition temperature, and the properties near the transition are driven by thermal fluctuations. These ...

Spontaneous superconducting currents in strontium ruthenate

Superconductivity is a complete loss of electrical resistance. Superconductors are not merely very good metals: they represent a fundamentally different electronic state. In normal metals, electrons move individually, and ...

Storing information with light

New photo-ferroelectric materials allow storage of information in a non-volatile way using light stimulus. The idea is to create energy efficient memory devices with high performance and versatility to face current challenges. ...

page 1 from 18

Electrical resistance

The electrical resistance of an object is a measure of its opposition to the passage of a steady electric current. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material.

Discovered by Georg Ohm in the late 1820s, electrical resistance shares some conceptual parallels with the mechanical notion of friction. The SI unit of electrical resistance is the ohm, symbol Ω. Resistance's reciprocal quantity is electrical conductance measured in siemens, symbol S.

The resistance of a resistive object determines the amount of current through the object for a given potential difference across the object, in accordance with Ohm's law:

where

For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current through or the amount of voltage across the object, meaning that the resistance R is constant for the given temperature. Therefore, the resistance of an object can be defined as the ratio of voltage to current:

In the case of nonlinear objects (not purely resistive, or not obeying Ohm's law), this ratio can change as current or voltage changes; the ratio taken at any particular point, the inverse slope of a chord to an I–V curve, is sometimes referred to as a "chordal resistance" or "static resistance".

This text uses material from Wikipedia, licensed under CC BY-SA