Electromagnetism — Part 2: Induction, generators and transformers: visual lesson, ICSE Class 10 Physics (Science Paper 1)

Lesson

Making electricity with magnets

Part 2 — a changing magnetic field can create a current. This idea powers every generator in a power station and every transformer on the way to your home.

In this lesson you will

Describe how moving a magnet near a coil induces a current, and what affects its size
Use Fleming’s right-hand rule to find the direction of an induced current
Name the parts of an AC generator and state its energy conversion; relate frequency and period of household AC
Give the advantages of AC and compare step-up and step-down transformers

Table of devices that use electromagnetic induction
Device	Idea used
Bicycle dynamo	Magnet turning near a coil
Power station generator	Coil turned in a magnetic field
Phone charger	Step-down transformer
Pole transformer	Step-down to 220 V

Diagram

Electromagnetic induction

Connect a coil to a galvanometer. Push a magnet into the coil: the needle deflects. Hold it still: no deflection. Pull it out: the needle deflects the other way. A current is induced only while the magnetic field linked with the coil is changing. Moving the coil instead of the magnet has the same effect. This is electromagnetic induction; the current is an induced current.

Concept

What makes the induced current larger?

The induced current is larger when: (1) the magnet or coil moves faster; (2) the coil has more turns; (3) a stronger magnet is used; (4) the coil has a soft iron core. It is reversed when the motion is reversed or the other pole is used. There is no induced current without relative motion (or another change in the field).

Table of changes and their effect on the induced current
Change	Effect on the deflection
Magnet moved in faster	Larger
Coil with more turns	Larger
Stronger magnet	Larger
Magnet pulled out instead	Reversed
Magnet at rest	Zero

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