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

Moving an electromagnet

Class practical

An electromagnet is now used instead of a permanent magnet with similar effects. This is to be expected, but it is satisfying to see in action.

Apparatus and materials

Copper wire, insulated with bare ends, 200 cm

C-cores, laminated iron, 2

Cell, 1.5 V in holder

Galvanometer, sensitive to e.g. 3.5–0–3.5 mA, 10 ohm resistance

Health & Safety and Technical notes


If a zinc chloride cell is used, it will polarize in 60 s or less and must be left overnight to recover. 

If an alkaline manganese cell is used, there is a danger of the cell overheating with a risk of explosion - complete the circuit for 30 s or less. 
 
If a re-chargeable cell (NiCd) is used, the wire will get very hot and the cell will be discharged in a few minutes - do the experiment as quickly as possible.

Read our standard health & safety guidance

It is possible to use a low-voltage power supply instead of the 1.5 V cell, but any ripple on the d.c. output can lead to confusion.

 

Procedure


Apparatus set-up

a Wind a coil of roughly 20 turns on one arm of a C-core. 

b Connect the coil by long leads to a galvanometer. This is Coil 1. 
 
c Wind a coil of 10 turns on one arm of the second C-core. 
 
d Connect this coil to the 1.5 V cell. This is Coil 2. 
 
e Coil 2 becomes an electromagnet. Bring it up to Coil 1, as shown. Observe the effect. 
 
f Take Coil 2 away again. Observe the effect. 
 
g Find out how the deflection on the galvanometer changes if the current in Coil 2 is reversed. 
 
f Investigate the factors which affect the deflection on the galvanometer. 


Teaching notes


Students will find that: 

  • there is only a current when Coils 1 and 2 are moving relative to each other; 
  • reversing the movement of Coil 2 reverses the deflection on the galvanometer; 
  • reversing the current of Coil 2 reverses the deflection on the galvanometer; 
  • faster movement results in a bigger deflection.  


This experiment was safety-checked in January 2005