Discover: A String of Lights

Connecting loads in separate loops has advantages.


Imagine that you are an air traffic controller, and you have to help planes land at night.  It would be very important for you to be able to turn on and turn off many lights at once.  It would also be important that lights would shine even if one or two lights stopped working.  By designing electric circuits with loops and switches in the right places, we can have the best possible results.

Using a ladder or stairs to climb a cliff  is like using a parallel circuit. If one rung breaks, the climber can still use the other rungs to reach the top of the cliff. In a parallel circuit, if one bulb/electrical device burns out, the rest will continue to work.

A parallel circuit can be compared to a maze where one end of the battery is the starting point. The wires can be compared to paths. A bulb acts as a bridge along a path. If the bulb is removed, a dead end is created along that path. But, you can still find other paths to create a circuit.

In this circuit, a single switch controls 5 lamps, but each lamp has its own loop to the power source.  That means you can turn on all 5 lamps at once, but if one lamp burns out, the others will still work.

  Try This!

Your Circuit

  • Electricity kit items: 2 lamps and 2  lamp holders, 4 connecting wires, battery holder or thick rubber band, switch
  • AA batteries or D-cell battery

Circuit A

Use three connecting wires to connect the switch 2 lamps, and battery together in one loop. Note how bright the lamps glow.




Circuit B

Use four connecting wires to connect the 2 lamps and battery together in two loops. You may include the switch.  When you have made the circuit properly, both lamps will have their own separate pathways to the battery.


The motor ran faster, and the lamp glowed brighter with two loops!  Remember that loads, such as the motor and the lamp, use electrical energy.  When they are connected in the same loop, they must share the electricity, which reduces the energy available for each one.  But, with two separate loops, the motor and the lamp do not share, and the motor runs faster and the lamp glows brighter.


How many different ways can you connect 5 lamps?

  Simulation

PhET Circuit Construction Simulation

  • Or use Yenka software

    •   Notebook

    Click on the icon to download the instructions for this activity. Save to your Electricity Notebook.


      Skill Builder

    Click a link below to learn how to: