Circuit Components (SQA National 5 Physics): Revision Note

Circuit components

• Common electrical and electronic components used in circuits can be represented by standard symbols

Symbols for circuit components

• You will be expected to know the symbol, function and application of the following components

  • Cell / battery

    • A source of potential difference (voltage) and electrical energy

    • A battery is two or more cells connected in series

  • Lamp

    • Converts electrical energy to light energy

    • Used as a source of light

  • Switch

    • Completes a circuit and allows current to flow when closed

    • Used to switch circuits on and off

  • Resistor

    • Fixed resistors have a constant resistance

    • Used to control the size of current in a circuit

  • Voltmeter

    • Used to measure potential difference (voltage)

    • Must be connected in parallel

  • Ammeter

    • Used to measure current

    • Must be connected in series

  • LED

    • Converts electrical energy to light energy

    • Only lights up when current flows in the correct direction

  • Motor

    • Converts electrical energy to kinetic energy

    • Used in appliances that move or rotate e.g. washing machine

  • Microphone

    • A microphone generates a voltage when sound reaches it

    • Used in telephones

  • Loudspeaker

    • Converts electrical energy to sound energy

    • Used in headphones

  • Photovoltaic cell

    • Produces a voltage when light falls on it

    • Used to provide energy for satellites and spacecraft

  • Fuse

    • Breaks the circuit by melting when the current is too high

    • Used to protects components from overheating

  • Diode

    • Allows current to flow through it in one direction only

    • Used to convert AC to DC

  • Capacitor

    • Stores energy as charge

    • Used in time delay circuits and electronic amplifiers

  • Thermistor

    • Resistance decreases as temperature rises

    • Used as a sensor in thermostats and heating systems

  • Light Dependent Resistor, LDR

    • Resistance decreases as light level rises

    • Used to control street lights

  • Relay

    • An electrically operated switch

    • Uses a small current in one circuit to switch on a much larger current in another

  • Transistor

    • A process device which acts as a switch

    • Used in electronic switching circuits