© boardworks ltd 2005 ks4 electricity - electromagnetism

© Boardworks Ltd 2005

KS4 Electricity - Electromagnetism


What is a magnetic field?

Where would you find a magnetic field?


Around every magnet is an invisible force field that will affect all magnetic objects inside it.

The magnetic field of a bar magnet is seen with iron filings.

N S

Magnetic field

What does the magnetic field around a bar magnet look like?

strongest field at poles

Where is the magnetic field strongest?


What materials will stick to magnets?

Look around the laboratory or your teacher will provide a tray.

See which materials will stick to a magnet and which materials will not.

Magnetic materials

Non-magnetic materials


Magnets and materials

N S

What materials are magnets made from? Iron or steel.

What materials will magnets stick to? Iron or steel.

And nickel!


Forces between magnets – experiment


Repulsion and attraction

Repel/attract

Repel/attract

Repel/attract

Unlike poles attract.

Like poles repel.


Separating coins

N S

How could you separate steel and gold coins using a magnet?

Steel coins would stick to magnet, gold coins would be left behind.


What does the magnetic field for a bar magnet look like?

In what direction do magnetic field lines

point?N North to South S


Revising magnetism I

Magnets are made from which materials? ___________

What are the ends of a magnet called? __________

What do we call the area around a magnet where a

magnetic force exists? __________________

What does the word attract mean? __________

What does the word repel mean? __________

Iron or steel

The Poles

The Magnetic Field

Pull together

Push apart


What will two north poles do if brought together? _____

What will two south poles do if brought together? ______

What will a north and a south pole do if brought

together? _______

What materials are attracted by magnets? ___________

Is magnetism a contact or non-contact force? _________

Repel

Repel

Attract

Iron and steel

Non-contact

Revising magnetism II


Electromagnets

A coil of wire acts like a bar magnet when it has an electric current flowing through it.

One end of the coil becomes a north-seeking pole.

One end of the coil becomes a south seeking pole.

This is called an electromagnet.


Making an electromagnet:

Apparatus:

Batteries

Wire

Iron Nail

What to do:

1. Wrap a coil of wire around the iron nail.

2. Connect the coil of wire to the batteries.

3. See how many paperclips you can pick up.


Results

How many paperclips could you pick up?

Can you think of any ways to make the electromagnet pick up more paperclips?

More batteries (more current)

Number of paperclips

Number of batteries

More turns of wire on the coil

Number of paperclips

Number of turns


Electromagnetic strength – experiment


The results for the number of drawing pins attracted to the electromagnet with no core are:

Electromagnetic strength - results

1 2 3

4 2 4 6

8 4 8 12

12 6 12 18

numberof cells

numberof coils

How does changing the current affect the strength of an electromagnet?

How does changing the number of coils affect the strength of an electromagnet?


Compare the results for the number of drawing pins attracted to the electromagnet with no core and an iron core:


1 2 3

4 2 4 6

8 4 8 12

12 6 12 18

numberof cells

numberof coils

1 2 3

4 6 8 10

8 8 12 16

12 10 16 22

numberof cells

numberof coils

What effect does an iron core have on the strength of an electromagnet?


Compare the results for the number of drawing pins attracted to the electromagnet with no core and a copper core:


1 2 3

4 2 4 6

8 4 8 12

12 6 12 18

numberof cells

numberof coils

1 2 3

4 2 4 6

8 4 8 12

12 6 12 18

numberof cells

numberof coils

What effect does a copper core have on the strength of an electromagnet?


Ways to make an electromagnet stronger

There are three ways to make an electromagnet stronger. Do you know them?

1. ___________________

2. ___________________

3. ___________________

More turns on the coil

More electrical current

Using an iron core S N

What happens if you turn the battery around in an electromagnet?

S

The poles on the coil reverse, north becomes south and south becomes north.


What do like poles do?

A. Attract and repel

B. Attract

C. Repel

D. Stick together


Which material below will not stick to a magnet?

A. Steel paper clip

B. Aluminium can

C. Iron nail

D. Steel key


Which of the below will not increase the

strength of an electromagnet?

A. More coils

B. More current

C. Less current

D. Iron core


In which direction do magnetic field lines

always point?

A. East to west

B. West to east

C. South to north

D. North to south


Which of the following is not a use of

electromagnets?

A. Fridge magnets

B. Loud speakers

C. Relays

D. Circuit breakers

© boardworks ltd 2005 ks4 electricity - electromagnetism

Documents

magnetic field strongest

magnetic field lines

south s slide

n s magnetic field

magnetic force

bar magnet

magnetic objects

strongest field