Circuit Diagrams
- The diagram below shows the various circuit symbols that could be used in circuit diagrams
Common circuit symbols
Functions of Most Common Components
- Switch: it turns the circuit on (closed), or off (open)
- Fixed resistor: it limits the flow of current
- As electrons flow through a resistor, they transform electrical potential energy into other forms of energy (i.e. thermal energy)
- Variable resistor: a resistor with a slider that can be used to change its resistance
- As the resistance of the variable resistor increases, the current in the circuit decreases and vice versa
- Thermistor: a resistor whose resistance depends on its temperature
- As temperature increases, the resistance of a thermistor decreases and vice versa
- Light-dependent resistor (LDR): a resistor whose resistance depends on the light intensity
- As light intensity increases, the resistance of a LDR decreases and vice versa
- Diode: it allows current to flow in one direction only
- It is often use for rectification - i.e. conversion of AC into DC
- Light-emitting diode (LED): it emits light when a current passes through it
- Light bulb: a resistor that transforms electric potential energy into such large thermal energy that energy is dissipated as light emitted to the surroundings
- Ammeter: it measures the current in the circuit
- Voltmeter: it measures the potential difference of an electrical component
Worked example
Which circuit diagram correctly represents a circuit with current flowing through?
- 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
Examiner Tip
The standard circuit symbols are given in the data booklet, so you do not need to memorise them. However, you must be able to identify them and draw them correctly.