• The diagrams below show the various circuit symbols that could be used in circuit diagrams. You will be expected to recognise and draw all of these
• The most common symbols are as follows:

Common circuit symbols

• The function of the most common components are:
  • 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. Used often 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 component
  • Voltmeter:?Use to measure the potential difference of an electrical component. Connected in parallel with component

• The more uncommon, yet relevant symbols, are as follows:

Other circuit symbols

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

• • For a circuit to be connected, the switch must be closed
    • This is either circuit?B?or?D
  • The other circuit symbol is a diode
    • Diodes only allow current to flow in one direction
  • Since current flow is from positive to negative, a forward-biased diode must point in this direction in order for the current to flow
    • This is seen in circuit?B