Current, potential difference and charge · GCSE Physics

Circuit symbols

Circuits are drawn with standard symbols: cell, battery, switch (open and closed), lamp, fuse, resistor, variable resistor, diode, LED, thermistor, LDR, ammeter and voltmeter.
An ammeter measures current and is connected in series. A voltmeter measures potential difference and is connected in parallel across a component.

For charge to flow through a closed circuit, the circuit must include a source of potential difference, such as a cell or battery.
Electric current is a flow of electrical charge. The size of the current is the rate of flow of charge.
Q = I t: charge (coulombs, C) = current (amperes, A) × time (seconds, s).
The current is the same at any point in a single closed loop.

Potential difference (pd, or voltage) is the energy transferred per unit of charge passing between two points. It is measured in volts (V).
A cell provides the potential difference that pushes charge around the circuit.

The current through a component depends on both the resistance of the component and the potential difference across it.
The greater the resistance, the smaller the current for a given potential difference.
V = I R: potential difference (V) = current (A) × resistance (ohms, Ω).

Electric current: The rate of flow of electrical charge, measured in amperes (A).
Charge: A property of particles such as electrons, measured in coulombs (C).
Potential difference: The energy transferred per unit charge between two points, measured in volts (V).
Resistance: How much a component opposes the flow of current, measured in ohms (Ω).
Ammeter: A meter connected in series to measure current.
Voltmeter: A meter connected in parallel to measure potential difference.
Closed circuit: A complete loop that current can flow around.
Coulomb: The unit of charge (C).