**Electric current** is a flow of electrical charge.

The size of the electric current is the rate of flow of electrical charge.

The amount of charge passing a point in the circuit can be calculated using the equation:

charge flow (coulombs, C) = current (amperes, A) × time (s)

**Q = I t**

When electric current flows, electrical work is done and energy transferred.

Electrical current transfers energy around circuits.

Current is measured using an **ammeter**. To measure the current through a component, the ammeter must be placed in series with that component.

Electric currents are measured in **amperes** (A). The resistance (R) of the circuit and the potential difference (V) across the component has an effect on the size of the current.

For electrical charge to flow through a closed circuit the circuit must include a source of **potential difference (voltage).**

Potential difference is the difference in the amount of energy that charge carriers have between two points in a circuit.

To measure the potential difference across a component, a **voltmeter** must be placed in **parallel** with that component in order to measure the difference in energy from one side of the component to the other.

Potential difference is also known as voltage and is measured in **volts** (V).

When an electric current moves through a conductor the moving electrons can collide with the ions in the metal. This makes it more difficult for the current to flow and causes **resistance**.

Electrical resistance is a measure of the opposition to current flow in an electrical circuit.

Resistance is measured in **ohms** (Ω).

There are several factors that affect the resistance of a conductor.

- material, e.g. copper, has lower resistance than steel
- length - longer wires have greater resistance
- thickness - smaller diameter wires have greater resistance
- temperature - heating a wire increases its resistance

Current, potential difference or resistance can be calculated using the equation:

potential difference (V)= current (I) × resistance (Ω)**V = I R**