What is the difference between current and voltage?

Current is the flow rate of charge; voltage is the energy transferred per unit charge that drives that flow.

Why is current the same everywhere in a series circuit?

There is only one path, and charge cannot accumulate, so the same rate of flow passes every component.

PhysicsGCSE, IGCSE & A Level

What is electric current?

Electric current is the rate of flow of electric charge, measured in amperes — one ampere is one coulomb per second.

Electric current explained

In metals the charge carriers are free electrons; in electrolytes they are ions. Conventional current is drawn from positive to negative, opposite to electron flow.

Current is conserved at a junction, which is Kirchhoff's first law and the basis of every parallel-circuit calculation.

Key formula

I = \dfrac{Q}{t}

Worked example

60\,\text{C}

passes a point in

20\,\text{s}

, the current is

3\,\text{A}

Examiner tip

Current is not used up around a circuit. Saying 'the current is used by the bulb' loses marks — energy is transferred, charge is not consumed.

Electric current: common questions

What is the difference between current and voltage?: Current is the flow rate of charge; voltage is the energy transferred per unit charge that drives that flow.
Why is current the same everywhere in a series circuit?: There is only one path, and charge cannot accumulate, so the same rate of flow passes every component.

Related terms

Ohm's law

Ohm's law states that the current through a metallic conductor is directly proportional to the potential difference across it, provided temperature stays constant.

Resistance

Resistance measures how strongly a component opposes the flow of electric current, and is defined as potential difference divided by current.

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