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

Cutting a magnetic field with a wire

Class practical

Students should previously have inserted a magnet into a coil and measured the e.m.f. generated. This is a simpler version showing first of all only one coil (or loop) of wire.

Apparatus and materials

mild steel yoke

Copper wire, insulated with bare ends, 200 cm

Magnadur magnets, 2

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

Health & Safety and Technical notes

Read our standard health & safety guidance



mild steel yoke

a Attach two Magnadur magnets to the steel yoke with opposite poles facing each other. 

b Connect a long lead of insulated copper wire to the galvanometer. 
c Move the wire through the field between the permanent magnets. 
d Try the effect of a coil of many turns (see picture) and see how this changes the deflection. 

Teaching notes

Students will find that: 

  • there is only a current when the wire and magnet are moving relative to each other 
  • the faster the magnet or wire is moved then the greater the current 
  • the current changes direction when the relative motion of the wire and the magnetic field changes direction 
  • the effect is greater when the wire is formed into a coil (because there is more wire moving across the magnetic field)  

This experiment was safety-checked in April 2006