Voltage/Potential Difference
Electricity and Magnetism

Lamps in parallel

Practical Activity for 14-16 PRACTICAL PHYISCS


The current flowing in a circuit increases as more lamps are added in parallel with each other.

Apparatus and Materials

  • Lamps (12 V 6 W) in holders, 4
  • Switches, single-pole, 4
  • Ammeter, 0 - 5 A (a demonstration one would be good for this)
  • Power supply, low-voltage

Health & Safety and Technical Notes

Read our standard health & safety guidance


  1. Connect the ammeter and the four lamp holders with the switches to the low voltage supply.
  2. Note the current as first one, then two, then more, lamps are switched on.

Teaching Notes

  • Any energy that you transfer can be measured in joules. As long as a power supply maintains the electric current through the lamp, you continue to obtain a stream of energy which can be measured:
    • by catching the light radiation on light-sensitive paper
    • by warming up water
    • by measuring the energy delivered by a motor.
  • So you can find out how many joules of energy are being transferred per second from the power supply to some other component.
  • As more lamps are connected across the power supply, the amount of energy transferred by the lamps to the environment in joules/second increases. So does the current in coulombs per second, registered by the ammeter. The rate of energy transfer increases in proportion to the current drawn from the power supply.

This experiment was safety-tested in October 2006

Limit Less Campaign

Support our manifesto for change

The IOP wants to support young people to fulfil their potential by doing physics. Please sign the manifesto today so that we can show our politicians there is widespread support for improving equity and inclusion across the education sector.

Sign today