Circuit Diagrams & Circuit Components (Cambridge (CIE) IGCSE Physics): 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

  • Students are expected to know what each component is and how it behaves in a circuit

Types of circuit components

Power supplies

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

Resistors

• Potential dividers, fixed and variable resistors, thermistors and light-dependent resistors (LDRs) are all used to control current

Thermistors

• A thermistor is a non-ohmic conductor (opens in a new tab) and a temperature-dependent resistor

• The resistance of a thermistor changes depending on its temperature

  • As the temperature increases, the resistance of a thermistor decreases and vice versa

Light-dependent resistors

• A light-dependent resistor (LDR) is a non-ohmic conductor and sensory resistor

• Its resistance automatically changes depending on the light energy falling onto it (illumination)

• As the light intensity increases, the resistance of an LDR decreases

Meters

• Ammeters and voltmeters are used to measure the current and potential difference

  • Ammeters are always connected in series whilst voltmeters are always connected in parallel

Switches and functional components

• Switches open and close a circuit and determine whether current can flow

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

  • Motors rotate

  • Lamps emit light

  • Heaters transfer thermal energy

  • Bells emit a sound

Electromagnetic components

• Magnetising coils, relays and transformers use electromagnetic effects

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

  • Transformers 'step up' and 'step down' current and potential difference

Fuses

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

Diodes

Extended Tier Only

• In addition to the above, the circuit symbol for a diode must also be recognised and drawn:

• Diodes are occasionally drawn with a horizontal line running through the middle of them

• Diodes only allow current to flow through them in one direction (see the diagram below)

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

• Light-emitting diodes (LEDs) behave in exactly the same way, but they emit light when current flows through them