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

Faraday's motor

Demonstration

To demonstrate the motor effect in a wire carrying an electric current.

Apparatus and materials

Shallow dish, 80 mm diameter and 20 mm high (Petri dish)

Sheet of conducting metal, i.e. lead or copper approx 30 mm by approx 100 mm placed in base of dish with one end folded at right angles to clear top of dish and form electrode terminal

Neodymium magnet (10 mm diameter) glued to top face of metal sheet and placed centrally

Copper sulfate solution, saturated

Fuse wire, 5 amp. Use rheostat to limit current

Copper rod, 16 SWG or thicker, approx 100 mm long

Stand and clamp

Crocodile clips, 2

Power supply (0-12 V DC), 5 amps

Reversing switch (optional)

Ammeter (optional) to keep current to around 5 amps 

Health & Safety and Technical notes


The apparatus can produce some gas if current is too high. 
 
Fuse wire may rupture if the current is too high, so the demonstration should be done behind a screen. Why not use a rheostat and ammeter to adjust the current? (Copper sulfate is toxic.) 
 
The copper sulphate should not be left in the dish after the experiment is complete since it tends to attack the iron of the magnet.

1 Neodymium magnets are available from Rapid Electronics or Middlesex University teaching resources. Insulate side of magnet with glue or ring of adhesive tape. 

2 Recent developments in magnet technology have made this possible using brine or copper sulfate solution as the liquid conductor, instead of mercury (used by Faraday). 
 
If you use copper sulfate solution, the device will deposit copper from solution so can only be operated for short periods. Brine does not prevent the problem. 
 
3 Copper wire can be salvaged from offcuts of electrical earthing cable or use a nail / toy car axle etc.

This experiment was submitted by Richard Walder from Eastbourne College.

Procedure


Apparatus set-up

a Connect the lead strip electrode, using a crocodile clip, to the reversing switch. 

b Wrap or solder fuse wire to one end of the copper rod. Suspend the copper rod from clamp with 5 amp fuse wire so that the rod just clears the lead strip and can rotate freely around the magnet without fouling the magnet or strip. 
 
c Connect the free end of fuse wire, using a crocodile clip, to the reversing switch. 
 
d Pour sufficient copper sulfate into dish to just cover the magnet. 
 
e Starting at zero, increase the voltage until the copper wire starts to rotate around the magnet (it may need a helping hand to start). Reduce the voltage once rotation is established in order to keep the current to around 5 amps. 
 
f Reversing the polarity will reverse the direction of rotation.

Teaching notes


1 The copper sulfate solution forms an electrical conductor since it has free ions and completes the electrical circuit. 

2 An interesting but unwanted side effect is the reduction of copper sulfate by electrolysis to copper metal. This can be seen forming like iron filings at the end of copper rod as it rotates. 
 
3 This was the first motor ever produced repeatedly by Michael Faraday in his laboratory at the Royal Institution, London.

This experiment was submitted by Richard Walder from Eastbourne College.

Weblinks


Rapid electronics

Middlesex University teaching resources

How to make a simple DC Motor