Energy & Green Tech

Improving EV batteries with real-world driving data

Most electric vehicles are equipped with an electronic brain that manages day-to-day battery performance and safety. This battery management system, or BMS, includes software that uses algorithms to monitor the overall health ...


New invention for more efficient atomic force microscopes

The basic principle of the atomic force microscope is very simple: an extremely thin, movable tip on a cantilever is moved over a surface that is being examined. Tiny forces on an atomic scale act between the tip and the ...


Bionic robot arms as flexible and gentle as an elephant's trunk

Artificial muscles and nerves made from the shape memory alloy nickel-titanium are making robot arms as supple and agile as their animal counterparts. But these artificial limbs also weigh less, will work tirelessly and can ...


Integrating metal microstructures in glass

Safe from harsh environmental conditions, electrically and thermally conductive, and with great lithographic resolution: Embedding thin metal microstructures in glass promises exceptional properties for a range of applications. ...

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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:


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