Circuit Symbols
- The diagrams below show the various circuit symbols that could be used in circuit diagrams
- The most common symbols are:
- The function of the most common components are:
- Cell / battery / D.C supply: Provides the circuit with a source of e.m.f. 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 it 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
- Thermistor: The resistance of a thermistor depends on its temperature. As its temperature increases, its resistance decreases and vice versa
- Light-dependent resistor (LDR): The resistance of an LDR depends on the light intensity. As the light intensity increases, its resistance decreases and vice versa
- Diode: A diode allows current to flow in one direction only. They are used to convert AC to DC 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
- 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
Examiner Tip
You must be able to recognise and draw all of these circuit symbols for the exam, as you will rarely be told within the exam question itself.