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While electrical technicians always use special components when repairing or installing electrical system, it's possible to make an electrical circuit with paper clips and other common items right at home.

Let's try a hands on experiment to get you thinking about how electrical circuits work!

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You will need:

  • A D battery
  • 2 pieces of insulated wire (if unavailable, you can always use aluminium foil cut and folded into strips)
  • Tape
  • A cardboard square, 8 cm by 13 cm
  • 2 paper clips
  • 1 metal thumbtack or nail
  • 1.5-volt light bulb (or a small flashlight bulb)

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Instructions:

  • Strip 2-3 cm of insulation from each end of the wires.
  • Take the first wire. Tape one end to the positive or β€œ+” terminal of the battery.
  • Tape or wrap the other end of this wire around one end of the first paperclip.
  • To make the switch, press one thumbtack or nail into the cardboard, through the end of the paperclip with the wire around it. Make sure the paperclip can pivot freely on the thumbtack or nail.
  • Straighten the other paperclip. Press one end into the cardboard near the first paperclip, but not through it. This is the contact point for the switch. When the switch touches the contact point, electricity flows.
  • Connect the other end of the straight paperclip to one side of the light bulb base. Tape it in place if necessary.
  • Connect the stripped end of the second wire to the other side of the light bulb base.
  • Tape the free end of this wire to the β€œ-” terminal of the battery.
  • Tape the battery and light bulb to the cardboard to hold them in place.
  • Move the paperclip switch to touch the contact point. The light bulb should turn on.

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Your final layout should look like this –

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Let's have a look at how this reflects railway track circuits...
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The circuit you have created can be classed as a DCΒ circuit – it is a closed path with the electrical current only flowing in one direction.

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A DCΒ track circuit along a railway works much the same way, and can be broken down into the same components.

A battery or solar panel will supply the power; cables in the tracks deliver the power through to the relay on the other end, and back through to the power source via the other rail in a complete circuit.

When the circuit is complete, the relay is energised and keeps the signals in a 'clear' position. If the circuit breaks, for example through a broken rail or failed power source, then the relay is de-energised and defaults to reporting the block of track as occupied – meaning that the system always fails in a safe way.

Trains are detected because their metal wheels and axles conduct the circuit as a short cut that bypasses the relay altogether. That is, trains short the circuit and de-energise the relay.

And as we've already established, a de-energised relay = an occupied track.

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How cool is that?

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