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Ohm's law states that the electric current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, [1] one arrives at the three mathematical equations used to describe this relationship: [2]
The resistance of a given element is proportional to the length, but inversely proportional to the cross-sectional area. For example, if A = 1 m 2 , ℓ {\displaystyle \ell } = 1 m (forming a cube with perfectly conductive contacts on opposite faces), then the resistance of this element in ohms is numerically equal to the resistivity of the ...
The resistance of a given object depends primarily on two factors: what material it is made of, and its shape. For a given material, the resistance is inversely proportional to the cross-sectional area; for example, a thick copper wire has lower resistance than an otherwise-identical thin copper wire.
Ohm's law states that the voltage across a resistor is proportional to the current passing through it, where the constant of proportionality is the resistance (). For example, if a 300- ohm resistor is attached across the terminals of a 12-volt battery, then a current of 12 / 300 = 0.04 amperes flows through that resistor.
The motor size constant ... is the resistance (SI unit, ohm) is the motor torque ... a running motor generates a back-EMF proportional to the speed. Once the motor's ...
Plot of the Wiedemann–Franz law for copper. Left axis: specific electric resistance ρ in 10 −10 Ω m, red line and specific thermal conductivity λ in W/(K m), green line. Right axis: ρ times λ in 100 U 2 /K, blue line and Lorenz number ρ λ / K in U 2 /K 2, pink line. Lorenz number is more or less constant.
An I–V curve which is a straight line through the origin with positive slope represents a linear or ohmic resistor, the most common type of resistance encountered in circuits. It obeys Ohm's law; the current is proportional to the applied voltage over a wide range. Its resistance, equal to the reciprocal of the slope of the line, is constant ...
Resistance R is proportional to the distance l between the electrodes and is inversely proportional to the cross-sectional area of the sample A (noted S on the figure above). Writing ρ (rho) for the specific resistance, or resistivity, =.