Cutting a magnetic field with a wire
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
Health & Safety and Technical notes
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.
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