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Ohm's law

Voltage drives charge through a conductor, and the resistance tells how strongly the conductor opposes the current. Ohm's law links the three quantities for an ohmic resistor, where the current is proportional to the voltage. Power is the energy converted per second, and it can be found as voltage times current. The unit of voltage is the volt, of current the ampere and of resistance the ohm.

Try it yourself

Ohm's law

U = RI

Ohm's law

P = UI

electric power

Symbols

$U$	voltage	V
$R$	resistance	$\Omega$
$I$	current	A
$P$	power	W

Example

A resistor of 4 Ω is connected to 12 V.

$I = 12/4 = 3$ A and $P = 12 \cdot 3 = 36$ W.

A larger resistance at the same voltage gives a smaller current, not a larger one.

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Part of Physics 1: Electricity.