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

Studying a commercial relay


If students have made a model relay, this demonstration will reinforce their learning.

Apparatus and materials

Cell, 1.5 V

Commercial relay, small

Power supply, low voltage, DC


Iron yoke

Electric motor, fractional horsepower

Magnadur (ceramic) slab magnets, 2

Copper wire, stiff, bare, SWG 32 and SWG 26

Clamp, or wooden support blocks

Crocodile clips, 2

Leads, 4 mm, 2

Health & Safety and Technical notes

Read our standard health & safety guidance

Choose a relay which will control a 12 V circuit. It is desirable to choose one whose internal workings can be seen, or which can be revealed by later dissection.



Studying a commercial relay

a Connect up the control circuit: cell, switch and relay.

b Connect up the circuit to be controlled: battery and motor.
c Show the small-current control circuit switching the large current motor.


Teaching notes

1 If students have made a model relay, this demonstration will reinforce the class experiment rather than spoil it. A commercial relay operates quickly and surely and can control a large current.

2 You could insert ammeters in both circuits. Both instruments should have the same range, so that the different sizes of the two currents will be graphically evident.


This experiment was safety-tested in April 2006


Related experiments

Making your own relay


Cookie Settings