Circuit Symbols (WJEC GCSE Science (Double Award)): Revision Note

Circuit Symbols

• All students in the WJEC GCSE examination will be expected to recognise the following standard symbols and be able to construct circuits using them:

Collection of Common Circuit Symbols

Included in the diagram are the most common circuit symbols needed for the exam

• The function of the most common components are:

  • Cell / battery: Provides the circuit with a source of voltage. 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 be changed

  • 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

  • Thermistor: The resistance of a thermistor depends on its temperature. As temperature increases, the resistance of the thermistor decreases and vice versa

  • Light-dependent resistor (LDR): The resistance of an LDR depends on the light intensity. As the light intensity increases, the resistance of the LDR decreases and vice versa

  • Diode: A diode allows current to flow in one direction only (towards the point of the triangle). They are used to convert alternating to direct current

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

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

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

• Each of these components have an electrical resistance that may impact the current in the circuit

  • However, the resistance of the ammeter and voltmeter are taken as negligible in exam questions

Drawing & Interpreting Circuit Diagrams

• Being able to draw and interpret circuit diagrams using circuit symbols is an essential skill in the electricity topic

• Electric circuit diagrams require the following to work effectively:

  • An energy source – This is a source of voltage so that a current can flow. This can be a cell, battery, or a power supply

  • A closed path or a complete circuit – Electrons need to flow in a complete loop for a current to flow. A circuit can be open and closed using a switch

  • Electrical components – These could act as sensors that respond to the environment (LDR, thermistor), or measure a value (ammeter, voltmeter), or transfer energy (LED, lamp). These must be drawn with the correct circuit symbol

• The key rules to remember are:

  • An ammeter is always connected in series

  • A voltmeter is always connected in parallel to the component the voltage is being measured

  • The direction of conventional current is always from the positive to the negative terminal of the power supply