Circuit Symbols (Oxford AQA IGCSE Combined Science Double Award)

Circuit Symbols

• All students in the GCSE examination will be expected to draw and interpret circuit diagrams using the following symbols:

Common circuit symbols

• The functions of the most common components are:

  • Cell / battery: Provides the circuit with a source of potential difference. A battery is two or more cells

  • Switch: Turn the circuit on (closed), or off (open)

  • Fixed resistor: A resistor limits the flow of current. A fixed resistor has a resistance that cannot change

  • Variable resistor: A resistor with a slider that can be used to change its resistance. These are often used in dimmer switches and volume controls

  • Diode: A diode allows current to flow in one direction only. They are used to convert A.C. to D.C. current

  • Light-emitting diode (LED): This is equivalent to a diode and emits light when a current passes through it. These are used for aviation lighting and displays (TVs, road signs)

  • Ammeter: Used to measure the current in a circuit. Connected in series with other components

  • Voltmeter: Use to measure the potential difference of an electrical component. Connected in parallel with the relevant component

Sensors

• Thermistor: The resistance of a thermistor depends on its temperature

  • As its temperature increases, its resistance decreases and vice versa

  • Thermistors are used in the thermostats of heating devices such as radiators and kettles

  • Thermostats regulate the temperature of an area or substance (e.g. ensuring a room stays at 20 °C)

• Light-dependent resistor (LDR): The resistance of an LDR depends on the light intensity of the surroundings

  • As the light intensity increases, its resistance decreases and vice versa

  • LDRs are used on street lamps, so they turn on automatically when it gets dark and the light intensity gets lower