8.3Chapter 8: Magnetism and Electromagnets

Electromagnets — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 6 1 quiz

📚 Alhussan Physics - Stage 8 Hub / Topical Revision

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Lesson summary

Physics 8.3 Electromagnets — Solenoids, Iron Cores and Magnetic Field Strength — Alhussan International Academy — Physics (Stages 7–9) notes: Describe how to make an electromagnet and how to change its strength.Fixed strength — A bar magnet has a fixed strength, but a magnet whos…

Current and field
Straight wire
Circular loop
Iron not steel
Medical use
Fixed strength — A bar magnet has a fixed strength, but a magnet whose strength can vary is more useful

Part 1 of 6What an electromagnet is

Fixed strength

A bar magnet has a fixed strength, but a magnet whose strength can vary is more useful.

Electromagnet

Electromagnet a coil of wire carrying a current, usually wound on a core of magnetic material, that can be switched on and off.

Current and field

A magnetic field is produced only while a current flows, so a switch turns the electromagnet on and off.

Part 2 of 6From a wire to a solenoid

Straight wire

The magnetic field lines around a single wire are circles, and the field gets weaker further from the wire.
Plotting compasses show the shape of the field.

Circular loop

The field lines at the centre of a loop are straight, and the field is stronger.

Solenoid

Solenoid a coiled cylinder made from lots of loops of wire.

Coiling concentrates the magnetic field inside the loops, making it much stronger than for a single loop.
The field has a similar shape to that of a bar magnet, with a north pole at one end and a south pole at the other.

Part 3 of 6The iron core

Core

A coil wound on a core of magnetic material is an electromagnet, and most cores are iron.

Effect

The core becomes magnetised by the field of the coil, which makes the electromagnet much stronger.

Iron not steel

Iron is easily magnetised and demagnetised, so it stops being a magnet when the current is switched off, whereas steel would stay magnetised.

Current

The current flows only in the wire; the iron is magnetised by the field.

Part 4 of 6Strength of an electromagnet

Factor	Effect on strength
Number of turns of the coil	More turns make a stronger electromagnet
Current	More current makes a stronger electromagnet
Type of core	A magnetic material in the core makes it stronger

Current
- It depends on the power supply and the type of wire used.

Part 5 of 6Electromagnets and permanent magnets

Permanent magnet	Electromagnet
Fixed strength	Strength can be varied
Always on	Can be switched on and off
Poles fixed	Poles reverse when the current is reversed

Uses

Large electromagnets move iron and steel in factories and scrapyards and drop the load when the current is turned off.

Medical use

A small electromagnet can remove iron or steel splinters from an eye.

Maglev

Electromagnets can lift a train off its track to reduce friction.

Part 6 of 6Investigating electromagnet strength

Wind insulated wire round an iron nail and connect it to a low-voltage power supply.

Change the number of turns, the independent variable.

Count how many paper clips the electromagnet picks up, the dependent variable.

Keep the current, nail and paper clips the same.

Repeat three times and calculate a mean.

Switch the current off between readings because the coil can become warm.

Key terms

Term	Meaning
Electromagnet	A coil of wire carrying a current, usually around an iron core, that acts as a magnet.
Solenoid	A coil made from many loops of wire.
Core	The magnetic material, usually iron, inside a coil.
Turns	The loops of wire in a coil.
Magnetic field	The region where magnetic materials experience a force.