© Boardworks Ltd 2003 Electromagnets Core Describe the pattern of the magnetic field due to currents in straight wires and in solenoids Describe applications.

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Electromagnets

Core• Describe the pattern of the magnetic field due to currents in straight wires and in solenoids • Describe applications of the magnetic effect of current, including the action of a relaySupplement• State the qualitative variation of the strength of the magnetic field over salient parts of the pattern• Describe the effect on the magnetic field of changing the magnitude and direction of the current.

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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

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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!

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Repulsion and attraction

Repel/attract

Repel/attract

Repel/attract

Unlike poles attract.

Like poles repel.

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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

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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

Magnetic field around a straight wire

• Use the right hand grip rule to find the field direction

Magnetic field around a solenoid

• Two rules to find the poles

• Grip rule no. 2• N and S rule

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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 strong the magnet is.

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Results

How many paperclips could you pick up?

Can you think of any ways to make the electromagnet stronger?

More batteries (more current)

Number of paperclips

Number of batteries

More turns of wire on the coil

Number of paperclips

Number of turns

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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.

relays

• http://www.explainthatstuff.com/howrelayswork.html

• A relay uses a small current to turn on a larger current

• Eg a car starter motor

Relay diagram

• The power source for both circuits may be the same (the resistance determines the size of the current)

• There are several other arrangements that would have the same effect eg a plunger arrangement

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What do like poles do? A. Attract and repel

B. Attract

C. Repel

D. Stick together

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Which material below will not stick to a magnet?

A. Steel paper clip

B. Aluminium can

C. Iron nail

D. Steel key

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Which of the below will not increase the

strength of an electromagnet?

A. More coils

B. More current

C. Less current

D. Iron core

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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

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Which of the following is not a use of

electromagnets?

A. Fridge magnets

B. Loud speakers

C. Relays

D. Circuit breakers

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Plenary: Magnetic Effect of Current Study the diagram of an electric bell, then put the statements into

the correct order

Current flows through electromagnet

Magnetic field produced

Magnetic field attracts armature

Armature moves towards electromagnet

Hammer strikes gong, circuit is broken

Armature no longer attracted to coil

Armature springs back

Circuit is complete again