Electromagnetic induction: magnet and coil
Push a magnet into a coil, hold it still and pull it out, and watch a galvanometer. Find what makes the induced voltage bigger and what reverses it.
Core concept
A changing magnetic field through a coil induces a voltage; faster change and more turns give a bigger voltage
Topic: Magnetism
In 1831 Michael Faraday found that moving a magnet: An object that pulls iron and steel towards it. All key words near a coil of wire makes a current: The flow of electricity through a wire, measured in amperes (A). All key words flow, with no battery at all. This is electromagnetic induction. A voltage: The push that makes electricity flow, measured in volts (V). All key words (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: One of the two ends of a magnet (north and south), where its pull is strongest. All key words, 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
- With 100 turns, push the magnet's N pole into the coil slowly and record the galvanometer.
- Hold the magnet still inside the coil, then pull it out, recording each time.
- Push it in fast, then use the coil with 200 turns.
- 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.