A level revision

Ohm's law

Ohm's law relates potential difference and current with resistance using the equation:

This equation shows that the current, I, is proportional to the potential difference, V.

This equation can easily be arranged to form expressions for both current and resistance.

Current-Potential difference graphs

Graphs of current against voltage can be used to identify electrical components

An ohmic conductor has an I-V graph which is just a straight line through the origin. This shows that the current flowing through them is directly proportional to the p.d. across them.

A filament lamp does not obey ohms law as the resistance does not remain constant to due an increase in heat at higher voltages.

A diode only allows current to flow in one direction and only then it will only let current pass until a certain minimum voltage has been reached. However small increases in voltage after the minimum voltage result in large increases in current.