Electromagnetic Induction: Start Here

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1. Push the magnet into the coil. The meter deflects. The illustration shows this first state.
2. Hold the magnet still: the meter returns to zero.
3. Pull the magnet out. The meter deflects in the opposite direction.

• Moving the coil while the magnet is fixed gives the same results. The motion of one relative to the other is what matters.
• Reversing the magnet pole also reverses the meter deflection.

While the magnetic field passing through the coil changes, the coil becomes a source of electrical energy. A voltage produced by a source is called an electromotive force (e.m.f.).

• Electromagnetic induction is the production of an e.m.f. when the magnetic flux linkage changes.
• If the circuit is complete, the induced e.m.f. drives an induced current. An open conductor can have an e.m.f. across its ends but no current.
• The key requirement is change. A strong but unchanging magnetic field gives no continuous induced e.m.f.

Large flux linkage can give zero e.m.f. if it remains constant. The next lessons make flux linkage measurable.