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Grade 10 Advanced About 20 min Version 1 Awaiting review Premium

Electromagnetic induction: magnet and coil

In 1831 Michael Faraday found that moving a magnet near a coil of wire makes a current flow, with no battery at all. This is electromagnetic induction. A voltage (an emf) is induced whenever the magnetic field passing through the coil changes. Nothing happens while the magnet is still. The induced voltage is bigger if the magnet moves faster, if the magnet is stronger, or if the coil has more turns. Reversing the motion, or using the other pole, reverses the direction of the current. Power stations, including Nepal's hydropower plants, generate electricity this way.

What you will learn

  • Show that a moving magnet induces a current in a coil.
  • Describe the factors that affect the size of the induced voltage.
  • Describe what reverses the direction of the induced current.

Before you start

  • Know what a magnetic field is.

Materials

  • A strong bar magnet
  • Coils of insulated wire with 50, 100 and 200 turns

Equipment

  • Centre-zero galvanometer and connecting leads

Procedure

  1. With 100 turns, push the magnet's N pole into the coil slowly and record the galvanometer.
  2. Hold the magnet still inside the coil, then pull it out, recording each time.
  3. Push it in fast, then use the coil with 200 turns.
  4. Turn the magnet round so its S pole goes in first.

How this simulation is simplified

  • Induced voltage = 0.2 mV × turns × speed factor (slow 1, fast 3), with its sign set by the pole and the direction of motion.