Download Electromagnetism Questions

ELECTROMAGNETISM
1.
(a)
Look at the pictures of household appliances.
Which two appliances have a motor inside them?
answer ............................................... and .................................................... [2]
(b)
John passes a wire through a card.
He connects the wire to a battery.
Look at the diagram.
He sprinkles iron filings onto the card to show the shape of the magnetic field.
Which is the shape of the magnetic field made by the wire?
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Choose from:
A
B
C
D
answer ....................................................... [1]
(c)
The diagram shows part of a DC generator. Look at the diagram.
Complete the diagram by adding labels to parts A and B.
[2]
[Total 5 marks]
2.
This question is about magnetic fields and forces.
(a)
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(i)
John passes a wire through a card. He connects the wire to a battery.
Look at the diagram.
2
He sprinkles iron filings onto the card to show the shape of the magnetic
field.
Which is the shape of the magnetic field made by the wire?
Choose from:
A
B
C
D
answer ....................................................... [1]
(ii)
He puts the wire between the poles of a magnet. Look at the diagram.
When he closes the switch, there is a current in the wire.
The wire moves.
Use Fleming’s left hand rule to predict the direction of motion.
Which way does the wire move?
Put a
ring
around the correct answer.
towards S
towards N
upwards
downwards
[1]
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(b)
The diagram shows part of a simple electric
motor.
The current is increased.
The motor spins faster.
Suggest two other ways of making the motor
spin faster.
1 .....................................................................................................................
2 ..................................................................................................................... [2]
[Total 4 marks]
3.
This question is about generating electricity.
(a)
Dave has some scientific equipment.
at the equipment.
He wants to generate electricity. Look
Explain how he can use this equipment to generate electricity. You may draw a
diagram as part of your answer.
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........................................................................................................................
........................................................................................................................ [2]
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(b)
Electricity is generated in power stations.
It is sent to homes through cables and transformers in the National Grid.
(i)
What is the frequency of this electricity in the UK?
..................................................................... Hz [1]
(ii)
Why is DC electricity not used with transformers?
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[Total 4 marks]
4.
Declan has some electrical appliances in his house.
(a)
Look at the diagram of an electric motor.
Declan connects the motor to the power supply. It spins round.
(i)
Declan passes more current through the motor. What happens to the
motor?
............................................................................................................... [1]
(ii)
He puts stronger magnets in the motor. What happens to the motor?
............................................................................................................... [1]
(iii)
Declan now uses a coil with fewer turns. What happens to the motor?
............................................................................................................... [1]
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(iv)
He changes the direction of the current. What happens to the motor?
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(b)
Declan has an electric razor. He plugs it into a special socket in the bathroom.
This socket contains an isolating transformer.
(i)
Why does he use an isolating transformer?
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............................................................................................................... [1]
(ii)
Transformers have a primary coil and a secondary coil.
What is special about the primary and secondary coils in an isolating
transformer?
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............................................................................................................... [1]
[Total 6 marks]
5.
This question is about transformers.
(a)
Batteries produce direct current. What sort of current do transformers produce?
........................................................................................................................ [1]
(b)
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(i)
Look at the diagram of a transformer.
6
Jenny has a 12 V lamp. She wants to use it from the 240 V mains. The
transformer she uses has 2000 turns on the primary coil. Calculate the number
of turns on the secondary coil. The list of equations may help you.
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answer .............................................. turns [2]
(ii)
Jenny uses a step-down transformer for her lamp. Write down one other
use of step-down transformers.
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............................................................................................................... [1]
[Total 4 marks]
6.
Transformers are normally used to change the size of an AC
voltage. A shaving socket has two outputs, 230 V and 115 V.
SHAVERS
ONLY
(a) What type of transformer changes the 230 V mains supply to
115 V?
..................................................................................................
………………………………………………....................... [1]
(b)
230 V
115 V
The input to the transformer is 230 V. There are 10 000 turns on the primary coil
of the transformer.
The output is 115 V. How many turns are there on the secondary coil?
Use the equations on page 2 to help you.
........................................................................................................................
........................................................................................................................
number of turns on secondary coil = .......................................................... [2]
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(c)
An isolating transformer is used between the 230 V mains supply and the 230 V
outlet.
Why is there an isolating transformer in a shaver socket?
........................................................................................................................ [1]
(d)
Naseer is reading about his new rechargeable shaver. He looks at the label on
the charger.
AC – DC adaptor
Input 230 V ~ 50 Hz
Output 2.8 V 1200 mA
What is the frequency of the mains electricity supply in the UK?
.......................................
[1]
[Total 5 marks]
7.
There are three types of transformer; step-up, step-down and isolating. Transformers
have a number of uses. Four uses are listed below.
Finish the table by writing each use in the correct column.
Uses
bathroom shaver socket
child’s train set
feeding national grid from power station
mobile phone charger
step-down
step-up
isolating
[Total 4 marks]
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8.
Step-up transformers are used at power stations to increase the voltage before
electricity is transmitted to the National Grid.
This transformer increases the voltage from 18 000 V to 225 000 V.
The current in the primary coil is 16 kA (1600A).
(a)
Explain how the construction of the transformer allows the voltage to be stepped
up by this amount.
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........................................................................................................................ [2]
(b)
Explain why electricity is transmitted at such high voltages.
In your answer use your ideas about
•
Energy loss
•
Current and voltage
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........................................................................................................................ [2]
(c)
Calculate by how much the power loss is reduced by stepping up the voltage to
225 000 V.
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........................................................................................................................ [2]
[Total 6 marks]
M Manser
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