GCSE Physics: Electricity and Circuits Guide

Current, voltage and resistance

Current (measured in amps) is the rate of flow of electrical charge. Potential difference, or voltage (measured in volts), is the energy transferred per unit of charge. Resistance (measured in ohms) opposes the flow of current.

Ohm's law

Ohm's law states V = I × R (potential difference = current × resistance), letting you calculate any one of the three values if you know the other two.

Series and parallel circuits

In a series circuit, current is the same everywhere and voltage is shared between components. In a parallel circuit, voltage is the same across each branch, and current is shared between branches.

Circuit components

A resistor limits current flow. A diode only allows current to flow in one direction. A thermistor's resistance changes with temperature, and an LDR's resistance changes with light level.

Common mistakes

• Mixing up how current and voltage behave differently in series versus parallel circuits.
• Rearranging Ohm's law incorrectly when solving for current or resistance.
• Confusing a thermistor (responds to temperature) with an LDR (responds to light).