The generator effect
If an electrical conductor moves relative to a magnetic field , or
if there is a change in the magnetic field around a conductor, a
potential difference is induced across the ends of the conductor
If the conductor is part of a complete circuit , a current
is induced in the conductor. This is the generator effect
The conductor must cut through the magnetic field lines. Moving a
wire parallel to the field lines induces nothing
Demonstration: move a magnet into a coil connected to a sensitive
ammeter. The needle deflects while the magnet is moving, returns to
zero when the magnet is still, and deflects the other way when the
magnet is pulled out
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The generator effect N S push in pushing the magnet IN centre-zero ammeter — the needle deflects one way N S pull out pulling the magnet OUT centre-zero ammeter — the needle deflects the OTHER way Moving a magnet into a coil (or moving the coil near a magnet) makes the coil CUT through magnetic field lines — and a potential difference is INDUCED across it. If the coil is part of a complete circuit, a current flows. Reverse the movement, or turn the magnet round, and the induced p.d. reverses. Hold the magnet still and NOTHING happens — no cutting of field lines, no induced p.d. A bigger p.d. comes from moving faster, a stronger magnet, or more turns on the coil. The induced current always makes its own magnetic field that OPPOSES the change that caused it — which is why you have to do work to keep the magnet moving. A bar magnet being pushed into a coil connected to a centre-zero ammeter; the needle deflected to one side; a second small diagram showing the magnet pulled out and the needle deflected the other way
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In the full topic
• The generator effect• Factors affecting the induced potential difference• The induced current opposes the changeRead the free physics topics →