Key stage 3 Physics Revision 1

Electricity, Magnetism, Electromagnetism

Use the following list to assess your knowledge of the key topics – You should decide if you know

the topic very well (), reasonably well () or not at all well ()

Objective

I can:

Self assessment

before revision

Self assessment

after revision represent simple circuits using symbols state a cell/battery provides an electric current which travels round the circuit

use ideas about complete circuits to describe how a switch works explain that the nature and number of components in a circuit affects the resistance and therefore the current flow

state that current in a series circuit is not used up by components state that cells and batteries are a chemical source of electrical energy explain the difference between energy and electric current in a circuit predict the current in branches of a parallel circuit apply the water model or a similar model to parallel circuits compare and contrast series and parallel circuits explain that electrical energy from the battery is transformed by a fuse to light and heat; this can cause it to melt

remember that the nerves are electrical conductors can give examples of electrical circuits being used to perform a variety of useful tasks

state that electrical energy is transferred around circuits and can be transformed in components,

explain how current behaves in electrical circuits state that electric current is conducted from 'the mains' to components in electrical circuits

state that some appliances transfer more energy than others (in a given time)

identify the power rating of common household electrical devices name materials that magnets attract state that magnets both attract and repel each other explain why attraction is not proof of magnetism describe how to show that magnetic materials block the action of magnetic fields

describe how to magnetise a magnetic material describe a method for measuring magnetic strength state that the Earth has a magnetic field, which attracts a freely pivoted magnet to line up with it

identify that for magnets to point north to south, the suspension mechanism must be almost completely unaffected by other forces

recall the shape of the magnetic field line pattern around a bar magnet, identify the factors that affect the strength of an electromagnet give examples of electromagnets being used in a wide range of applications

draw the field pattern of an electromagnet made from a straight coil explain the effect of an iron core, using ideas of magnetising materials

Key words

Use your exercise book, text books and other revision material to give definitions for the following

key words and phrases related to Electricity, Magnetism and Electromagnetism.

Ammeter

Amp

Attraction

Domain

Electric current

Electromagnet

Magnetic field

Magnetic field

Magnetic material

North seeking pole

Parallel circuit

Repulsion

Resistance

Series circuit

Solenoid

South seeking pole

Voltage

Voltmeter

Sample Exam Questions

The mark scheme for these questions, along with further practice questions, can be found at

http://mrblackstone.wikispaces.com/

Level 4

1. The diagram below shows a pen.

The pen is held up by two magnets, one in the stand and the other in the pen.

N

S

magnet in stand

magnet in pen

pen

stand

(a) On the dotted lines above, label the North pole and the South pole of the magnet in the pen.

Use the letters N and S.

1 mark

(b) John put a block of metal between the two magnets as shown below.

N

S

magnet in stand

magnet in pen

stand

block of metal

The block of metal became a magnet.

(i) On the dotted lines above, label the North poles and the South poles of both the block of metal and the magnet.

Use the letters N and S.

1 mark

(ii) What metal could the block be made of?

.............................................................

1 mark

(c) John repeated the experiment using a piece of wood instead of a block of metal. The pen did not stay up. Give the reason for this.

........................................................................................................................

1 mark

maximum 4 marks

2. Alice connects four light bulbs for her model house, as shown. She puts the bulbs into the holes in the back wall.

(a) When Alice turns the switch on, the bulbs do not light up. The batteries are not flat. None of the bulbs is broken. Why do the bulbs not light up?

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1 mark

(b) Alice makes the circuit work. When she turns the switch on, the bulbs are not very bright. What must Alice add to the circuit to make the bulbs brighter?

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1 mark

(c) The four bulbs in the circuit are the same. Which statement is correct? Tick the correct box.

Each bulb is the same brightness.

Each bulb is a different brightness.

The bulbs at the top are brighter.

The bulbs at the bottom are brighter.

1 mark

The diagrams show two ways to write the model house.

bulb A

bulb A

bulb B

bulb B

bulb C

bulb Cbulb D

bulb D

circuit 1 circuit 2

(d) (i) In circuit 1, bulb B breaks and goes out. What happens to the other bulbs in this circuit?

.............................................................................................................

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1 mark

(ii) In circuit 2, bulb C breaks and goes out. What happens to the other bulbs in this circuit?

.............................................................................................................

.............................................................................................................

1 mark

(e) In circuit 2, Alice adds another switch so that she can turn bulb A off while the other bulbs stay on. Write the letter S on circuit 2 to show where Alice should add the switch.

1 mark

Maximum 6 marks

Level 5

3. (a) Debbie put a paper cup into a glass beaker. She glued a magnet in the bottom of the paper cup. She glued another magnet in the bottom of the beaker. The magnets repelled.

N

S

S

N

magnet

magnet

paper cup

glass beaker

diagram A

not to scale

What two forces act on the paper cup and its contents to keep it in this position?

1. ...........................................................

1 mark

2. ...........................................................

1 mark

(b) Debbie put 5 g of aluminium rivets into the paper cup. It moved down a little as shown in diagram B.

N

S

S

N

aluminiumrivets

diagram B

not to scale

Debbie plotted a graph to show how the mass of aluminium rivets affected the distance the cup moved down.

6

5

4

3

2

1

00 10 20 30 40 50 60

mass (g)

distance papercup moveddown (mm)

(i) Use the graph to find the mass that made the cup move down 4 mm.

............... g

1 mark

(ii) Why did the graph stay flat with masses greater than 40 g?

.............................................................................................................

1 mark

(c) Debbie removed the 5 g of aluminium rivets and put 5 g of iron nails into the cup.

N

S

S

N

ironnails

diagram C

not to scale

The paper cup moved down more with 5 g of iron nails than with 5 g of aluminium rivets as shown in diagram C. Give the reason for this.

.....................................................................................................................

.....................................................................................................................

1 mark

maximum 5 marks

4. The diagram shows a circuit for controlling an electric motor.

lamp 1 lamp 2

switch Bswitch A

M

motor

This circuit can make the motor turn forwards or backwards.

Complete the table to show which lamp, if any, is lit and in which direction, if any, the motor turns.

The first row has been done for you.

switch A

up

up

down

down

switch B

down

up

up

down

lamp 1 forwards

Which lamp,if any, is lit?

In which direction, ifany, does the motor

turn?

4 marks

Level 6

5. David made two electromagnets as shown below. He used paper-clips to test the strength of each electromagnet. He switched on the power supply in both circuits.

power supplyon

coil iron core

power supplyon

coil steel core

(a) How can you tell that the strength of both electromagnets is the same?

.................................................................................................................

.................................................................................................................

1 mark

(b) David switched off the power supply in both circuits. The paper-clips fell off the iron core, but not off the steel core.

power supplyoff

coil iron core

power supplyoff

coil steel core

Why is iron used, rather than steel, for the core of an electromagnet? Use the diagrams above to help you.

......................................................................................................................

......................................................................................................................

1 mark

(c) David used a sensor to measure the strength of an electromagnet.

He placed the sensor 25 mm from the electromagnet and increased the current in the coil.

He repeated the experiment with the sensor 50 mm from the electromagnet.

The graph below shows his results.

reading onthe sensor

current (amps)

50 mm fromelectromagnet

25 mm fromelectromagnet

(i) How did the distance of the sensor from the electromagnet affect the reading on the sensor?

................................................................................................................

................................................................................................................

1 mark

(ii) How did the size of the current in the coil affect the strength of the electromagnet?

................................................................................................................

................................................................................................................

1 mark

(iii) What else could David do to an electromagnet to change its strength?

................................................................................................................

................................................................................................................

1 mark

maximum 5 marks

6. Peter measured the current through each of three similar bulbs in a parallel circuit.

A3

A2

A1

He had only one ammeter and he placed it first at A1, then A2, then A3, in order to measure the currents.

The table shows his results.

position of ammeter current, in amps

A1 0.14

A2 0.16

A3 0.15

(a) He expected the current readings to be the same for each bulb but found they were different.

Suggest two reasons why the readings were different.

1. ................................................................................................................

2. ................................................................................................................

2 marks

(b) Peter then measured the current at A4 and recorded it as 0.45 A. He concluded that the current at A4 could be calculated by adding together the currents through each of the bulbs at positions A1, A2 and A3.

A4

He added two more similar bulbs to his circuit, in parallel. The current through each bulb was 0.15 A. Use Peter's conclusion to predict the current at A4 with the 5 bulbs in the circuit.

................ A

A4

1 mark

(c) Peter left the circuit connected overnight. He used a datalogger to measure the current at position A4 at regular intervals of time. The next morning the bulbs were dim.

Using the axes below, sketch (do not plot) how the current at position A4 might change with time.

Indicate on the graph:

(i) The correct labels for each axis, including the correct units.

(ii) The shape of the graph you would expect to obtain.

00

2 marks

Maximum 5 marks

Level 7

7. A reed switch is made of two iron strips inside a glass tube. The iron strips close together when a magnet is brought near. They spring apart again when the magnet is removed.

(a) Hilary set up the circuit shown below. She tried to close the reed switch using an electromagnet.

She closed switch E but the electromagnet was not strong enough to close the reed switch.

(i) Give two ways Hilary could increase the strength of the electromagnet.

1. .........................................................................................................

2. .........................................................................................................

2 marks

(ii) Hilary increased the strength of the electromagnet. The reed switch closed. The iron strips were magnetised as shown below.

She reversed the current in the coil of the electromagnet. On the diagram below, label the poles of the iron strips when the current was reversed.

1 mark

(b) (i) Iron and steel are both magnetic materials. Explain why the strips must be made of iron and not steel.

.............................................................................................................

.............................................................................................................

1 mark

(ii) She replaced the reed switch with a piece of copper wire. The current through the bulb increased.

Explain why more current flowed through the bulb when the reed switch was replaced with copper wire.

.............................................................................................................

.............................................................................................................

1 mark

maximum 5 marks

8. The diagram shows a rectangular coil and circuit. It has two iron rods in it. The rods are parallel and touching. They are free to move.

(a) When the switch is closed, the two rods move apart.

(i) Explain why this happens.

.............................................................................................................

.............................................................................................................

.............................................................................................................

.............................................................................................................

2 marks

(ii) The switch is then opened to break the circuit. What, if anything, happens to the two iron rods?

.............................................................................................................

.............................................................................................................

1 mark

(b) One of the two iron rods is taken out and replaced with a brass rod. The rods are parallel and touching. What, if anything, will happen to the rods when the switch is closed? Explain your answer.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

2 marks

Maximum 5 marks

Level 8

9. The flow of water through tubes can be used as a model to explain some of the rules about electrical circuits.

waterflowingout at cm /sz 3

waterflowingin at cm /sx 3

waterflowingout at cm /sy 3

pipe X

pipe Y

pipe Z

The diagram shows a junction in a water pipe.

The rate of flow in the pipes is measured in cm3/s.

(a) What is the relationship between the rate of flow in the three pipes, X, Y and Z?

......................................................................................................................

1 mark

(b) The diagram below shows a ‘water circuit’, in which water is forced round by a pump. The rates of flow at two places are written on the diagram.

(i) At what rate is water flowing:

into the pump? ………………………. cm3/s

out of the pump? …………………….. cm3

/s

1 mark

(ii) The ‘water circuit’ can be used as a model of an electrical circuit. Each part of the ‘water circuit’ is equivalent to a part of an electrical circuit.

What is the electrical equivalent of the water?

.............................................................................................................

1 mark

A family, who did not understand electricity very well, always made sure there was a bulb in each of the light fittings in their house. They were afraid that electricity would escape from an empty light socket when the switch was turned on.

(c) Explain why electricity does not escape from an empty light socket.

......................................................................................................................

......................................................................................................................

......................................................................................................................

1 mark

Maximum 4 marks

10. The simplified diagram shows a device which protects people from being electrocuted when

using power tools such as hedge cutters. The wire in one part of the circuit is shown darker to make the circuit clearer.

When the armature is attracted towards the soft iron core, the contacts are pushed apart and break the circuit.

powertool

point X

hinge

softironcore

powersupply

case

coil A coil B

contacts compressedspring

hinge

steelarmature

(a) The power tool, coil A and coil B are all in the same series circuit. Coils A and B are wound in opposite directions.

The current in the coils has no magnetic effect on the armature. Explain why.

......................................................................................................................

......................................................................................................................

......................................................................................................................

1 mark

(b) A gardener accidentally cuts the wire at point X. Current from the power supply starts to flow through the gardener to earth.

What effect will this have on the armature? Explain your answer.

......................................................................................................................

......................................................................................................................

......................................................................................................................

......................................................................................................................

3 marks

Maximum 4 marks