# 13.3.3 Ohm’s Law

When a PD of V is applied across a resistor, a current I flows through the resistor.

It turns out that V is proportional to I for a lot of common components used in electrical circuits. This relationship is called Ohm’s Law.

$V=IR$

where the constant of proportionality R has come to be known as resistance.

A word of caution: The symbol V is used to denote an electric potential in the Electric Field chapter. Here the same symbol V is used to denote a potential difference. In a less messed up world Ohm’s Law should be written as $\Delta V=IR$.