Ohms Law & Non-Ohmic Conductors

gcse physics chapter 3 : electricity

Ohm's Law

States that the current through a conductor is directly proportional to the potential difference across it.

Ohmic conductor

An electrical conductor that obeys Ohm's Law, such as fixed resistors, wires, and heating elements.

Ohm's Law equation

V = IR, where V is the potential difference, I is the current, and R is the resistance.

Constant temperature

Ohm's Law is relevant only at constant temperatures.

I-V graph for an ohmic conductor

A straight line graph through the origin.

Filament lamp

An example of a non-ohmic conductor where current and potential difference are not directly proportional.

Effect of temperature on resistance in filament lamps

Resistance increases as the temperature of the filament increases.

Diode

A non-ohmic conductor that allows current to flow in one direction only.

Forward bias in diodes

When current flows in the direction of the arrowhead symbol.

Reverse bias in diodes

When no current flows due to very high resistance in the opposite direction.

Linear components

Circuit elements that obey Ohm's Law and have a straight line I-V graph.

Non-linear components

Circuit elements that do not obey Ohm's Law and have a non-straight line I-V graph.

Examples of linear components

Fixed resistors, wires, heating elements.

Examples of non-linear components

Filament lamps, diodes, LEDs, LDRs, thermistors.