Circuit Diagrams & Circuit Components (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award)): Revision Note

Circuit components

What are circuit symbols?

• The diagram below shows the circuit symbols that could be used in circuit diagrams to represent circuit components

  • You will be expected to know what each component is and how it behaves in a circuit

Circuit symbols represent these components in circuit diagrams

Types of circuit components

Power supplies

• Cells, batteries, and power supplies all supply current to the circuit

Resistors

• Fixed and variable resistors are used to control current

  • The resistance of a fixed resistor is constant

  • The resistance of a variable resistor can be adjusted

Meters

• Ammeters and voltmeters are used to measure the current and voltage at different points in a circuit

  • Ammeters are always connected in series

  • Voltmeters are always connected in parallel

Switches and functional components

• Switches open and close a circuit to control the flow of current

• Functional components perform specific roles when current passes through them:

  • Motors rotate

  • Lamps emit light

  • Heaters transfer thermal energy

Fuses

• Fuses protect expensive components from current surges and act as a safety measure against fire

Generators & diodes

Extended Tier Only

• In addition to the above, you should be able to recognise and draw the circuit symbols for

  • a generator

  • a light-emitting diode (LED)

Generators

• A generator is a device which produces current

  • A d.c. generator is a source of direct current (d.c.)

  • An a.c. generator is a source of alternating current (a.c.)

Generator circuit symbol

Generators are a type of power supply. They can be a source of d.c. or a.c.

Light-emitting diodes (LEDs)

• Light-emitting diodes (LEDs) are a type of diode

• They illuminate when placed in the correct direction (forward bias) when a current flows in a circuit

• Since the LED has a visual response to current, it can be used to indicate the presence of a current in a circuit

LED circuit symbol

LEDs indicate the presence of a current because they illuminate when current flows through them

• Diodes only allow current to flow through them in one direction, as shown in the diagram below

  • This is the direction that the triangle points in the diagram

• LEDs behave in the same way, but they emit light when current flows through them

LEDs in a circuit

When travelling in the same direction as the LED, current can flow and the LED illuminates. If the LED is flipped, it prevents current from flowing and does not illuminate