electromagnetism motors and generators

7/24/2019 Electromagnetism Motors and Generators

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1 of 29 Boardworks Ltd 2007

KS3 Revision

8J Magnets andElectromagnets


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8J Magnets and Electromagnets

Contents

Magnetic materials

Magnetic fields

Electromagnets

Summary activities


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Which of the metals below are magnetic metals?

silver (Ag)

Magnetic materials


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Ag

A magnetic material is attracted to a magnet.

Magnetic materials

Only iron (Fe), nickel (Ni) and cobalt (Co) are magnetic.


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Magnetic or non-magnetic?


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Contents

Magnetic materials

Magnetic fields

Electromagnets

Summary activities


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Forces between magnets experiment


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NS

The iron filings feel the effect of the magnetic field andshow the direction of the forces in this region.

The region around a magnet where it has a magnetic effectis called its magnetic field.

When a magnetic material is placed in a magnetic field it will

experience a force.

What is a magnetic field?


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weakest field furtheraway from poles

What is the shape and direction of the lines of force in themagnetic field around a bar magnet?

N S

Shape of a magnetic field

Where is the magnetic field strongest?

strongestfield

at poles

strongestfield

at poles


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Bring the north poles of two bar magnets together.

What happens to the magnets?

Viewing magnetic fields: N poles together

N SS N

Next, bring the two north poles as close to each other aspossible and place a piece of paper on top of the magnets.

Carefully scatter iron filings onto the paper.Draw the pattern created by the iron filings.


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NS

Magnetic field pattern: N poles together

What do you notice about the pattern of the lines of forcein the region between the two north poles?


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Bring the north and south poles of two bar magnets together.

What happens to the magnets?

Viewing magnetic fields: N and S poles together

S N S N

Next, put the north and south poles close to each other,without letting them touch, and place a piece of paper on top.

Carefully scatter iron filings onto the paper.

Draw the pattern created by the iron filings.


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NN

How does this pattern compare with the pattern betweenthe two north poles?

Magnetic field pattern: N and S poles together

What do you notice about the pattern of the lines of forcein the region between the north and south poles?

S S


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1. When two like poles (e.g. two north poles ortwo south poles) are put together, they repeleach other.

Magnetic fields summary

2. When two unlike poles (e.g. a north and asouth pole) are put together, they attract each

other.

3. Scattering iron filings around a bar magnet

makes it possible to see the lines of force of themagnetic field.


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A magnet can be made by magnetizing a material which isattracted to a magnet, e.g. a paper clip.

Stroke a magnet along the paperclip from one end to theother and then starting from the same place, repeat the

movement. The more times this is done, the moremagnetic the clip becomes.

Hold a nail in a magnetic field and hit it with a hammer.

Put a magnetic material in a strong magnetic field.

Making a magnet

There are three methods that can be used to make a magnet:


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Contents

Magnetic materials

Magnetic fields

Electromagnets

Summary activities


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Making an electromagnet

When electricity is passed through a coil of wire, the coil hasa magnetic field around it. This is called an electromagnet.

If the coil of wire is wrapped around a piece of iron, such asan iron nail, the magnetic field gets stronger.


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An iron core at the centre of a coil of wire increases thestrength of an electromagnet.

Two experiments can be carried out to investigate the otherfactors that can affect the strength of an electromagnet:

Investigating an electromagnet

1. Investigate how the number of coils affects thenumber of paper clips attracted to an electromagnet keep the current the same in this experiment.

2. Investigate how the size of the current affects thenumber of paper clips attracted to an electromagnet

keep the number of coils the same in this experiment.


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Number of coilsNumber of paper

clips attracted

0

20

40

60

80

Remember keep the current the samethroughout this experiment!

Investigating an electromagnet results 1

0

8

18

31

46


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Current (A)Number of paper

clips attracted

01

2

3

4

5

Remember keep the number of coils the samethroughout this experiment!

Investigating an electromagnet results 2

012

23

38

49

60


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Graph to show how the number of coils affects the

strength of an electromagnet.

0

10

20

30

40

50

0 20 40 60 80 100

Investigating an electromagnet graph 1

number of coils

numberofclipsattracte

d


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Graph to show how the current affects thestrength of an electromagnet

0

10

20

30

40

50

60

70

0 1 2 3 4 5

Investigating an electromagnet graph 2

current (A)

number

ofclipsattracted


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What advantages doesan electromagnet haveover a permanentmagnet?

Which metals would the

electromagnet attract?

A large electromagnet is used in a scrap yard to pick upand move heavy pieces of scrap metal.

Using electromagnets scrap yards


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The circuit for a door bell includes an electromagnet.

Using electromagnets door bells


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Lifts, cars and other large electrical machines use highcurrents.

Using electromagnets relay

A relay, which includes an electromagnet, is used to allow

a small current in one circuit to control a large current inanother circuit.


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Label the diagram electric bell


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Label the diagram - relay


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1. When electricity is passed through a coil of wire, the coilbehaves like a magnet and has a magnetic field around it

this is an electromagnet.

Electromagnets summary

wrap the coil of wire around an iron core;

increase the number of coils;

increase the size of the current.

3. An electromagnet can be easily turned on and off.This is why electromagnets can be used inscrapyards and as switches in electrical devices.

2. There are three ways to make an electromagnet stronger:


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Contents

Magnetic materials

Magnetic fields

Electromagnets

Summary activities


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Glossary

attraction The force that pulls things together,e.g. opposite poles of two magnets.

electromagnet A magnet made by passing electricitythrough a coil of wire, which often has a core inside.

magnet An object that has a magnetic field and canattract magnetic materials.

magnetic field The area around a magnet where itsmagnetic force can be felt.

magnetic materials Materials that are attracted to amagnet, e.g. iron, cobalt and nickel.

magnetism The non-contact force of a magnetic field.

other, e.g. like poles of two magnets.


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Anagrams


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Magnetism true or false?


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Multiple-choice quiz


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KS4


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El i d


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What is the link between movement, magnetism and electriccurrent?

Electromagnetism and movement

Wi i ti fi ld


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Wire in a magnetic field

Ch i th di ti f th f


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The direction of the force acting on a wire in anelectromagnetic field can be reversed by:

The direction of the force is therefore relative to both thedirection of the magnetic field and the current.

reversing the current reversing the magnetic field

Changing the direction of the force

Flemings left hand rule


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It is possible to predict the direction of the force acting ona wire its motion if the direction of the current or themagnetic field are known. Flemings left-hand rule isused to do this.

Flemings left-hand rule

thuMb = Motion

First finger = magnetic Field

seCond finger = Current

Increasing the size of the force


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Increasing the size of the force

Coil in a magnetic field


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Coil in a magnetic field

The motor effect: true or false?


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The motor effect: true or false?


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What are electric motors?


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What are electric motors?

How many items do you own that contain an electric motor?

An electric motor is a device thatconverts electrical energy into

mechanical energy to produce aturning effect.

Most motors are powered using direct

current (DC), which is produced bycells and batteries.

Motors powered by mains electricity

use alternating current (AC).These motors use electromagnetsrather than permanent magnets.

How does an electric motor work?


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How does an electric motor work?

DC electric motor simulation


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DC electric motor simulation

How do we increase motor strength?


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Would the same strength motor be used in both of these?

How can the strength of an electric motor be increased?

How do we increase motor strength?

increase the strength of the magnet

increase the current flowing through the coil

increase the number of turns on the coil


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Inducing current in a wire


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duc g cu e t a e

Flemings right-hand rule


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It is possible to predict the direction of the induced currentproduced by a generator if the direction of the force (ormotion) or the magnetic field are known. Flemings right-hand rule is used to do this.

g g

First finger = magnetic Field

seCond finger = Current

thuMb = Motion

What is electromagnetic induction?


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g

When current flows through a wire held in a magnetic field,a force is created that moves the wire.

The opposite is also possible: if a

wire is moved across a magneticfield, a current is produced. This iscalled electromagnetic induction.

Induction also occurs if a magnet ismoved in a coil of wire, or if a coil ofwire rotates in a magnetic field.

In all these methods of inducing a current, the wire andmagnetic field move perpendicular to each other. If theymove parallel to each other, no current is induced.

Inducing current in a coil


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g

What are generators?


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A generator is a device that converts mechanical energyinto electrical energy. It is the opposite of an electric motor.

Power stations use generators

to produce electricity on a largescale. Mechanical energy isprovided by rotating turbinesthat can be powered by:

high-pressure steam incoal, oil, gas and nuclearpower stations

wind in wind turbines

falling water in hydroelectric power stations

How do AC generators work?


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AC generator simulation


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Increasing the size of the induced current


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How can the size of an induced current be increased?

In a power stationgenerator, anelectromagnet is oftenused as this can provide

a stronger magnetic fieldthan is possible with apermanent magnet.

increase the speed at which the coil rotates

increase the strength of the magnetic field

increase the number of turns in the coil

increase the total area of the coil.

Factors affecting induced current


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Induction: true or false?


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Glossary


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alternating current A current that constantly changesdirection. It is produced by most electrical generators.

commutator The part of a motor that enables the coil torotate using direct current.

direct current A current that always flows in the samedirection. It is produced by cells and batteries.

generator A device that converts mechanical energy into

electrical energy. induction Generating a current in a wire by moving the

wire in a magnetic field, or by moving a magnet inside a coil.

motor A device that converts electrical energy intomechanical energy.

slip rings The parts of a generator that enable therotating coil to produce alternating current.

Anagrams


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Multiple-choice quiz


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electromagnetism motors and generators

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