Welcome to practical physicsPracticle physics - practical activities designed for use in the classroom with 11 to 19 year olds

Lamps in parallel


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


a Connect the ammeter and the four lamp holders with the switches to the low voltage supply.

b Note the current as first one, then two, then more, lamps are switched on.  

Ammeter and 4 lamps


Teaching notes

1 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.

2 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-checked in October 2006 


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