Electromagnetic Induction

Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★☆☆ Minimal safety procedures required

Categories: Electricity, Magnetism

Alternative titles: Faraday’s Law – Classic Induction Demo

Summary

A bar magnet moved through a solenoid induces a voltage, detected by an electrometer. This demonstrates Faraday’s law of electromagnetic induction, showing how changing magnetic flux generates an electromotive force (emf).

Procedure

Connect a solenoid in parallel to an electrometer.
Insert the bar magnet into the solenoid and then remove it quickly.
Observe the electrometer as the needle or digital readout changes, showing an induced voltage.
Repeat with different speeds: move the magnet slowly to produce a weak emf, and more quickly to produce a stronger emf.
Reverse the magnet’s pole and note the opposite direction of the induced voltage.

Links

Electromagnetic induction - ibPhysicsHelp:

Demonstration of Electromagnetic Induction - IGCSE Physics - Chris Gozzard (That Physics Guy):

📄 Faraday’s Law – Electromagnetic Induction - UCSC Physics Demonstration Room: https://ucscphysicsdemo.sites.ucsc.edu/physics-5c6c-demos/electromagnetism/faradays-law-electromagnetic-induction/

Variations

Compare results using a weak bar magnet versus a strong neodymium magnet.
Change the angle of the magnet’s motion relative to the solenoid axis.
Use solenoids with different numbers of coils to show how more loops increase the induced emf.

Safety Precautions

Handle magnets carefully to avoid pinching fingers or damaging equipment.
Do not connect the solenoid directly to a power source in this setup.
Use proper supports to prevent the solenoid or stand from tipping over.

Questions to Consider

Why does moving the magnet quickly produce a stronger induced voltage? (Faster motion causes a faster change in magnetic flux, producing a larger emf.)
What determines the direction of the induced voltage? (Lenz’s law states that the induced emf opposes the change in magnetic flux.)
Why is no emf induced when the magnet is held still in the solenoid? (There is no change in magnetic flux, so no induction occurs.)
How does increasing the number of coils affect the induced emf? (More coils increase the total flux linkage, producing a stronger induced voltage.)