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ElectromagnetismGCSE Physics


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Learning Intentions Recall the significant link between

electricity and magnetism

Observe how a magnetic field caninteract with a conducting wire

State how electricity can be generated


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Electrical Generators


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Investigate How does a magnet affect the loop of

conducting wire?


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What has to

happen for the

current to flow?

How is the direction

of the current flowing

related to the magnet?

How is it

possible toincrease the

amount of

current? Is

there morethan one way

of doing this?

How is itpossible for

current to flow

without moving

the magnet?


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The Not-so-Missing Link Magnetism is closely related to Electricity.

These two characteristics combine to make

one of the fundamental forces in physicsknown as Electromagnetism.

Where there is a magnetic field there is the

potential to make an electric current flow

Where there is a flow of an electric currentthere is an associated magnetic field.


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Uniform

Magnetic Fieldbetween poles


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Move the wire

through the

magnetic field


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Making Electricity Move the wiredown cutting through the

magnetic field

0

Induces a current


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Making Electricity Move the wire up cutting through the

magnetic field

0

Induces a current in

the other direction


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0

0

No Current Induced when the

movement of

the wire

does not

cut through

the magnetic

field lines

the

wire does

not move


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Electromagnetic Induction(pg156) This time use a wire coil (solenoid) and

move the magnet in and out

0 0

Magnetmoved in

Magnet

moved out
http://micro.magnet.fsu.edu/electromag/java/faraday2/http://micro.magnet.fsu.edu/electromag/java/faraday2/http://micro.magnet.fsu.edu/electromag/java/faraday2/http://micro.magnet.fsu.edu/electromag/java/faraday2/


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Induced Current Move the magnet into the coil and a

current is induced in one direction

Move the magnet out of the coil and acurrent is induced in the other direction

As soon as the motion stops the currentwill stop

For a current to be induced the magnetfield lines need to continually be cuttingthrough the wires


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Increase the SIZE ofcurrent/voltage Increase the speed of the movement of

the magnet towards/away from the coil

Use a more powerful magnet (moremagnetic field lines produced)

Increase the number of coils in the wire

(more wire being cut through by magneticfield lines)


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For current to flow The magnetic field lines must continually

be cut through by the wire (through the

lines of force) Work is done against the force of the

magnet and an energy transfer occurs

Kinetic Electrical


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Learning Intentions Recall the significant link between electricity

and magnetism

Recognise how a solenoid can induce acurrent in a coil of conducting wire

State the need for AC supplied to a solenoid to

continually induce a current

Understand how a transformer can be used to

change voltage between two circuits


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How does it work? Alternating Current

(AC), one way and

then another The magnetic field

lines are cutting

through the wires inthe secondary coil-

inducing a current!


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PrimaryCoil

SecondaryCoil

Pass a current through a coil

of wire and a magnetic field is

created.

When a magnetic field is at right

angles to a wire, a current is

induced in that wire

I th C t d


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Primary

CoilSecondary

Coil

Increase the Current and

the associated magnetic

field becomes stronger

A stronger magnetic field

will induce a larger

current in that wire

D th C t d


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Primary

Coil

Secondary

Coil

Decrease the Current and

the associated magnetic field

becomes weaker.

A weaker magnetic field

will induce a smaller

current in that wire

A t hi h i k t


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Primary

CoilSecondary

Coil

A current which is kept

constant in one direction is

known as Direct Current (D.C.)

If the magnetic field does not vary

then the current will no longer

be induced and will not flow

A t hi h fl i


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Primary

CoilSecondary

Coil

A current which flows in

one direction and then in

the other direction is

called an AlternatingCurrent (A.C.)

If the magnetic field is changing

all the time then a current will

continually be induced.


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Transformers (pg 161) What is a transformer?

A transformer consists oftwo coils

wrapped around a laminated soft ironcore.

Primary

Coil

Secondary

Coil


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Transformers SymbolIron Core
http://elchem.kaist.ac.kr/vt/chem-ed/electron/devices/graphics/trfm-sym.gif


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Types of Transformers Primary coils < Secondary coils

Step Up

The Iron Core links the two coils magnetically


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Step Up A step up transformer has more turns of

wire on the secondary coil, which makes

a larger induced voltage in the secondarycoil.

It is called a step up transformer because

the voltage output is stepped up


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Step Down Transformer Primary Coils > Secondary Coils

Step Down

The Core is made of iron so it can be easily

magnetised and demagnetised.


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Step Down A step down transformerhas less turns

of wire on the secondary coil, which

makes a smaller induced voltage in thesecondary coil.

It is called a step down transformer

because the voltage outputis stepped down.


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Transformers EquationVoltage Across Primary

Voltage Across Secondary

Number of turns on Primary

Number of turns on Secondary=

Vp Np

VS NS=


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Worked Example A voltage of 240V is applied to a primary

coil of200 turns. What is the voltage

across the secondary coil if it has 10turns?

Vp NpVS NS

=

200VS 10

=240

VS = 240 x10200

= 12 VoltsVS


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Learning Intentions Recall the significant link between electricity

and magnetism

Recognise how the electrical power generated

by a turbine is A.C.

Recall how electricity is transmitted through outthe country by The Grid

State the need for step-up and step-downtransformers for nationwide electricitydistribution


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A.C. Generator Alternating Current Generator (alternator)

- Page 158

http://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htm
http://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htmhttp://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htmhttp://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htmhttp://www.sciencejoywagon.com/physicszone/otherpub/wfendt/generatorengl.htm


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Katie Explains ACgenerators-
http://localhost/var/www/apps/conversion/tmp/scratch_6/ac%20generator.mov


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The National Grid (pg 159) Electricity generated a power

station is distributed to homes,shops, schools factories etc acrossthe country by a network of cablescalled the National Grid.

Step up Transformers are usedbeforetransmission on the Grid

Local Step down Transformers are

used before consumption byhomes, schools etc


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Why use Transformers? Page 160 and 161


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Lets get active Match the statements to the pictures to

make up the process for which electricity

is distributed across our beautifulcountry


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The power is then supplied to the homes, factories,offices etc for their own consumption.

The electrical power is connected to the National Grid

which is a network of cables stretching over thecountry. It is important that the voltage is high in thesecables.

A Transformerdoes not create more energy bystepping up the voltage. The power generated is equal

to that consumed. The voltage is increased so that thecurrent is reduced. This means less energy will be lostas heat in the cables (smaller resistance).

The voltage needs to be stepped down to a lowervalue by local transformers

In Power Stations, the alternators are driven by hugeturbines, spun round by the high pressure steam. Alarge current is produced.

Transformers are used to step up the voltage beforethe electrical power is distributed across the country


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To finish with Page 164

Questions 11 and 12

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