Revision of simple circuit components

• Devices that have more than one function

  • Some devices can function as input devices as well as output devices
• Output components

  • Light
  • Movement
  • Sound
  • Heat
• Output devices that can also function as process or control devices

  • Light-emitting diodes (LEDs)
• Control devices

  1. Control devices (also called switches) control the outputs in electrical circuits

  2. When a switch is on, there is output and when it is off, there is no output
• Figure 12.1 shows how an electrical system works. It has three types of components: an input device that puts electrical energy into the system, an output device that changes the input energy into an output (such as light), a switch that controls the energy that reaches the output
• Electric motors can work as output devices to drive a locomotive and as input devices when used as brakes to slow the train down by transforming kinetic energy into electric energy
• Output devices

  • Lamps (bulbs, globes)
  • Motors
  • Buzzers
  • Heaters
  • Resistors
• LEDs create the lights you see shining from electronic devices such as TV sets. They function as output devices when they shine with coloured light and as process or control devices in an electric circuit when they let electric current through in only one direction
• Input devices

  1. Several devices can be used as inputs to electrical circuits

  2. Three types of input devices are: electrochemical cells, generators, solar panels
• Devices that can function as input and output devices


  • Electric motors can function as both input and output devices
• Simple circuit components


  • Input device
  • Output device
  • Switch
• Short circuits occur when there is almost no resistance to the current in the circuit, causing the current to be very strong
• The large current in a short circuit can cause the cell to become hot and go flat quickly
• A circuit will only function if the loop is unbroken
• LEDs


  • create the lights you see shining from electronic devices such as TV sets
• Prevent short circuits

  Properly wired electrical circuits in houses are protected from short circuits by circuit breakers on the distribution board of the house
• LED


  • Functions as an output device when it shines with a coloured light
  • Functions as a process or control device in an electric circuit when it lets electric current through in only one direction
• Ways short circuits can happen in houses

  • The insulation of electrical wires in the roofs of some old houses become brittle and crumbles allowing wires that are not insulated to touch each other
  • The insulation on the leads of appliances such as vacuum cleaners becomes frayed and the exposed copper wires touch each other
  • The wires inside a plug tear loose from the pins and the ends of the wires that have been stripped of insulation touch each other
• Electric circuit


  A closed loop of wires or leads that connect components
• Short circuits can happen in houses when wires that are not insulated touch each other