# 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

#### 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.

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

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