Ohm's Law
Ohm's law states that for many conductors, V = IR: the potential difference across a conductor is proportional to the current through it, at constant temperature.
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Statement of Ohm's law
Ohm's law states that for a conductor at constant temperature, the potential difference V across it is directly proportional to the current I through it: V ∝ I, or V = IR, where R is the resistance of the conductor. So R = V/I; the unit of resistance is the ohm (Ω): 1 Ω = 1 V/A.
Ohmic and non-ohmic conductors
Conductors that obey Ohm's law (e.g. many metals) are called ohmic; a plot of V vs I is a straight line through the origin. Filament bulbs, diodes, and some devices are non-ohmic: R changes with V or I.
Using Ohm's law
Ohm's law is used to find current when V and R are known (I = V/R), voltage when I and R are known (V = IR), or resistance when V and I are known (R = V/I). It applies to the whole circuit or to a single resistor.
When a filament bulb gets hotter as it glows, does its resistance stay constant? What would that do to the V–I graph?