4.Main Content
experiments
Cutting a magnetic field with a wire
Class experiment
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𢠥.5 mA, 10 ohm resistance
Safety
Read our standard health & safety guidance
Procedure
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