· web viewthe fierce battle of the currents between nikola tesla and thomas edison forged a...

AQA Physics P3.3 Scheme of Work

Keeping Things Moving

Overview

The Big Picture for this unit

Without electricity where would humanity be? The fierce battle of the currents between Nikola Tesla and Thomas Edison forged a technological path that we are still treading at an enormous pace today.

Electric currents produce magnetic fields. Forces produced in magnetic fields can be used to make things move. This is called the motor effect and is how appliances such as the electric motor create movement. Our ability to exploit the motor effect of electricity has allowed us to develop into the technological society of the 21st Century.

Many appliances do not use 230 volts mains electricity. Transformers are used to provide the required potential difference. Without transformers we couldn’t distribute vast amounts of electricity all over the world and we wouldn’t be able to charge laptops and mobile phones. Without electricity where would humanity be?

Key Questions to ask students whilst teaching this unit

If electricity can kill you, how can it save lives?Do bigger batteries make bulbs brighter?Are battery-powered appliances safe in the bathroom?Does electricity leak away?Does the colour of the wire make a difference? Is electricity pure energy?Is it true that ‘volts jolt but current kills’?Is lightning part of a circuit?Is electricity natural or artificial?Aren’t current and voltage both just ways of measuring electricity?What are we paying for when we use electricity?Where does electricity go when we switch off?What is the point of earthing an appliance if earth doesn’t conduct?Do we ever lose control of electricity?Is static really electricity?Do efficient electric kettles work quicker?What makes a battery rechargeable?If nerves are conductors, does the body have a battery?Can you destroy electricity?How can a battery be flat if current has flowed back into it?Will electricity generation always cause problems?Is total sustainability compatible with cheap electricity?

Common misconceptions held by students

Electricity is energy

AQA GCSE Physics P3.3 Scheme of Work: Keeping Things Moving T. Baylis

Keeping Things Moving – Outline lesson sequenceLesson Main Focus of lesson Main LOs Key activities Assessment Link to spec.Lesson 1 Electromagnets Understand that a current in a

conductor produces a magnetic field and that this is the basis for electromagnets, applications of which include their use on cranes for lifting iron or steel.

Ask the students to explain what happens when two magnets are brought together.

Demonstrate and explain electromagnet and permanent magnet

Demonstrate and explain uses of electromagnetism.

Exam question sheet.

Exam Questions a) When a current flows through a wire a magnetic field is produced around the wire.

Lesson 2 The Motor Effect Understand the principle of the motor effect and know how to use Fleming’s Left-hand Rule to identify the direction of the force produced.

Know how the size and direction of the force produced can be altered.

Demonstrate and explain motor effect.

Students build model motors

Ask the students to make a list of everyday devices that use electric motors.


Exam Questions b) The motor effect and its use.c) The size of the force can be increased by:

1. Increasing the strength of the magnetic field

2. Increasing the size of the current.

d) The conductor will not experience a force if it is parallel to the magnetic field.e) The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed.

Lesson 3 Electromagnetic Induction

Understand the principle of electromagnetic induction.

Remind students of the National Grid demonstration in Physics 1.

Complete a labelled diagram of a transformer and the National Grid.

Explore the difference between an iron core transformer and an step down transformer.


Exam Questions a) If an electrical conductor ‘cuts’ through a magnetic field a potential difference is induced across the ends of the conductor.

b) If a magnet is moved into a coil of wire a potential difference is induced across the ends of the coil.


Lesson 4 Transformers Understand the structure of the transformer.

Explain how a transformer works.

Understand the difference between a step-up transformer and a step-down transformer.

Use the transformer equation.

Students plan to make a model transformer using C-cores and insulated wire.


Exam Questions c) If an electrical conductor ‘cuts’ through a magnetic field a potential difference is induced across the ends of the conductor.

d) If a magnet is moved into a coil of wire a potential difference is induced across the ends of the coil.

Lesson 5 Transformers in Action Understand the difference between a switch mode transformer and a conventional transformer.

Know the advantages and uses of switch mode transformers.

Remind students of the investigation they planned last lesson.

Carry out the investigation planned last lesson to see how the output voltage of a transformer depends on the number of turns.

Students report back on their findings.

Introduce the transformer equation

V P

V S=

NP

N S .

Complete the diagrams of step-up and step-down transformers.


Exam Questions g) The potential difference across the primary and secondary coils of a transformer are related by the equation:Vp / np = Vs / nsh) If transformers are assumed to be 100% efficient,the electrical power output would equal the electrical power input.Vp x Ip = Vs x Isi) Switch mode transformers operate at a high frequency, often between 50 kHz and 200 kHz.j) Switch mode transformers are much lighter and smaller than traditional transformers working from a 50 Hz mains supply. Candidates should be aware that this makes them useful for applications such as mobile phone chargers.k) Switch mode transformers use very little power when they are switched on but no load is applied.


Lesson 1 – Electromagnets

Specification Reference P3.3.1

a) When a current flows through a wire a magnetic field is produced around the wire.

Students should be able to: Understand that a current in a conductor produces a magnetic field and that this is the basis for electromagnets, applications of which include their use on cranes for lifting iron or steel.

Activities

Ask the students to explain what happens when two magnets are brought together.

Show the students how an electromagnet can attract and repel a permanent magnet. Also show how the strength of the electromagnet depends on the current in the coils.

Demonstrate uses of electromagnetism.

Explain circuit diagrams of practical devices like an electric bell and a circuit breaker.

Explain how a loudspeaker works. Draw a diagram of its action.


Resources

Bar magnets, iron filings

Long nails, coil wires, paper clips, power supply

Electric bell, circuit breaker

Demonstration equipment for magnetic field around a wire and solenoid;

S-cool revision topic ‘Magnetism and Electromagnetism’ can be found in the GCSE Physics section at www.s-cool.co.uk or by searching for ‘electromagnetism’.

Assessment Opportunities

Use of data to draw a conclusion.

AFL open ended question.

Exam questions.

Learning Outcomes

All students must know:

Describe the effect that magnets have on each other and on magnetic materialsDraw basic magnetic field patterns for a bar magnetDescribe the key elements of an electromagnet including the coil and iron core

Should:

Explain the function of basic electromagnetic devices

Could:

Interpret diagrams of electromagnetic appliances in order to explain how they work

Safety and Technicians’ Notes

Ensure students are not exposed to dangerous amounts of electricity.

Check CLEAPPS for further information.


http://www.s-cool.co.uk/

Lesson 2 – The Motor Effect


b) The motor effect and its use.c) The size of the force can be increased by:

3. Increasing the strength of the magnetic field

4. Increasing the size of the current.d) The conductor will not experience a force if it is parallel to the magnetic field.e) The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed.

Students should be able to: Understand the principle of the motor effect and know how to use Fleming’s Left-hand Rule to identify the direction of the force produced.

Know how the size and direction of the force produced can be altered.

Activities

Think through what happens when two magnets interact. What will happen to a magnet and an electromagnet.

Demonstrate the motor effect with a rod on a model rail track. Show how Fleming’s left hand rule can be applied. Show that a rod parallel to the magnetic field will not move.

Let the students use model motors. Get them to change the strength of the magnetic field, by removing one magnet. Also run the motor from one, two, three and then four cells.

Ask the students to make a list of everyday devices that use electric motors.

Find out how maglev trains are being developed for use across the world.


Resources

Demonstration equipment for the motor effect (rail track) and motor kits.

Useful information on an electric motor can be found at www.schoolscience.co.uk by searching for ‘electric motors’. An interactive motor demonstration can be found at www.walter-fendt.de/ph14e/electricmotor.htm



AFL open ended questions.

Exam questions.

Learning Outcomes


The motor effectThe force is increased in a stronger magnetic field The force is increased with more current

Should know:

Fleming’s left hand (motor) rule

Could know:

The construction of an electric motor





http://www.walter-fendt.de/ph14e/electricmotor.htm

http://www.schoolscience.co.uk/

Lesson 3 – Electromagnetic Induction


e) If an electrical conductor ‘cuts’ through a magnetic field a potential difference is induced across the ends of the conductor.

f) If a magnet is moved into a coil of wire a potential difference is induced across the ends of the coil.

Students should be able to:

Understand the principle of electromagnetic induction.

Activities

Remind students of the National Grid demonstration in Physics 1. The output of the power station (25 kV) is increased to around 400 kV in the Grid. It is then reduced to 33 kV and finally 230 V for houses. What devices do this?

Complete a labelled diagram of a transformer and the National Grid.

Explore the difference between an iron core transformer and an step down transformer. What are the pros and cons of each type?


Resources

Magnets, sensitive voltmeters, insulated wire, computer access.

http://phet.colorado.edu

Nelson Thornes Physics page 258.

Nelson Thornes Physics CD-ROM Physics P3 3.3 Transformers animation




Exam questions.

Learning Outcomes


How a transformer worksTransformers only work with a.c.How step-up and step-down transformers are used in the National Grid

Should know:

High voltage is used in the National Grid to reduce current and energy losses by heating

Could know:

Eddy currents in the core reduce the efficiency of transformers





http://phet.colorado.edu/

Lesson 4 – Transformers


g) The basic structure of a transformerh) An alternating current in the primary coil

produces a changing magnetic field in the iron core and hence in the secondary coil. This induces an alternating potential difference across the ends of the secondary coil. Knowledge of laminations and eddy currents in the core are not required.

i) In a step-up transformer the potential difference across the secondary coil is greater than the potential difference across the primary coil.

j) In a step-down transformer the potential difference across the secondary coil is less than the potential difference across the primary coil.

Students should be able to:

Understand the structure of the transformer.

Explain how a transformer works.

Understand the difference between a step-up transformer and a step-down transformer.

Use the transformer equation.

Activities

Students plan to make a model transformer using C-cores and insulated wire.

Go over how a transformer works. Plan an investigation, based on the

apparatus already used, to find out how the number of turns on the primary and secondary coils affect the transformer output


Resources

An experiment that shows the basic principle of any transformer can be found at www.practicalphysics.org/go/Experiment_347.html

Nelson Thornes Physics page 258.

Nelson Thornes Physics CD-ROM Physics P3 3.3 Transformers animation.




Learning Outcomes


How a transformer worksTransformers only work with a.c.How step-up and step-down transformers are used in the National Grid

Should know:

High voltage is used in the National Grid to reduce current and energy losses by heating

Could know:



ICT Access?


http://www.practicalphysics.org/go/Experiment_347.html

http://www.practicalphysics.org/go/Experiment_347.html

Lesson 5 – Transformers in Action


g) The potential difference across the primary and secondary coils of a transformer are related by the equation:Vp / np = Vs / nsh) If transformers are assumed to be 100% efficient,the electrical power output would equal the electrical power input.Vp x Ip = Vs x Isi) Switch mode transformers operate at a high frequency, often between 50 kHz and 200 kHz.j) Switch mode transformers are much lighter and smaller than traditional transformers working from a 50 Hz mains supply. Candidates should be aware that this makes them useful for applications such as mobile phone chargers.k) Switch mode transformers use very little power when they are switched on but no load is applied.

Students should be able to: Understand the difference between a switch mode transformer and a conventional transformer.

Know the advantages and uses of switch mode transformers.

Activities

Remind students of the investigation they planned last lesson.

Carry out the investigation planned last lesson to see how the output voltage of a transformer depends on the number of turns.

Students report back on their findings.

Introduce the transformer equation V P

V S=

NP

N S . Complete the diagrams of step-up and step-down transformers.


Resources

Iron C-cores, insulated wire, demonstration transformer.

Computer simulations of transformer action can be found at www.micro.magnet.fsu.edu/electromag/java/transformer/index.html




Exam questions.

Learning Outcomes


Step-up transformers increase voltage; step-down decrease voltage

The transformer equation: V P

V S=

NP

N S

Should know:

How step-up and step-down transformers are used in the National Grid

Could know:



Ensure students are not exposed to dangerous levels of electricity.

Take care not to drop C-Cores on feet.



http://www.micro.magnet.fsu.edu/electromag/java/transformer/index.html

http://www.micro.magnet.fsu.edu/electromag/java/transformer/index.html

Student Checklist

P3.3 Keeping things moving Before During Revision

1. Understand that a current in a conductor produces a magnetic field and that this is the basis for electromagnets, applications of which include their use on cranes for lifting iron or steel.

2. Understand the principle of the motor effect and know how to use Fleming’s Left-hand Rule to identify the direction of the force produced.

3. Know how the size and direction of the force produced can be altered.

4. Understand the principle of electromagnetic induction.

5. Understand the structure of the transformer.

6. Explain how a transformer works.

7. Understand the difference between a step-up transformer and a step-down transformer.

8. Use the transformer equation.

9. Understand the difference between a switch mode transformer and a conventional transformer.

10.Know the advantages and uses of switch mode transformers.


Glossary

Alternating current Electric current in a circuit that repeatedly reverses its direction.

Cable Two or three insulated wires surrounded by an outer layer of rubber or flexible plastic.

Circuit breaker An electromagnetic switch that opens and cuts the current off if too much current passes through it.

Conservation of energy Energy cannot be created or destroyed.

Coulomb (C) The unit of electrical charge, equal to the charge passing a point in a (direct current) circuit in 1 second when the current is 1 A.

Direct Current Electric current in a circuit that is in one direction only.

Efficiency Useful energy transferred by a device / total energy supplied to the device.

Electric current Flow of electric charge. The size of an electric current (in amperes, A) is the rate of flow of charge.

Electrical energy Energy transferred by the movement of electrical charge.

Electromagnetic induction

The process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of force of a magnetic field.

Field line See magnetic field line.

Force A force can change the motion of an object (in newtons, N).

Frequency of an alternating current

The number of complete cycles of oscillation per second, equal to 1/the time period. The unit of frequency is the hertz (Hz).

Line of force See magnetic field line.

Magnetic field line Line in a magnetic field along which a magnetic compass points; also called a magnetic field line or field line.

Magnetic poles Ends of a bar magnet or a magnetic compass.

Motor effectWhen a current is passed along a wire in a magnetic field and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field.


National Grid The network of cables and transformers used to transfer electricity from power stations to consumers (i.e. homes, shops, offices, factories, etc.).

North pole North pointing end of a freely suspended bar magnet or of a magnetic compass.

Potential differenceA measure of the work done or energy transferred to the lamp by each coulomb of charge that passes through it. The unit of potential difference is the volt (V).

Power The energy transformed or transferred per second. The unit of power is the watt (W).

South pole South-pointing end of a freely suspended bar magnet or of a magnetic compass.

Split-ring commutator Metal contacts on the coil of a direct current motor that connects the rotating coil continuously to its electrical power supply.

Step-down transformer Electrical device that is used to step down the size of an alternating voltage.

Step-up transformer Electrical device that is used to step up the size of an alternating voltage.

Switch mode transformer

A transformer that works at much higher frequencies than a traditional transformer. It has a ferrite core instead of an iron core.

Transformer Electrical device used to change an (alternating) voltage. See also Step-up transformer and Step-down transformer.

Volt (V) The unit of potential difference, equal to energy transfer per unit charge in joules per coulomb.

Wasted Energy Energy that is not usefully transferred.

Watt (W) The unit of power.


Glossary

Alternating current Electric current in a circuit that repeatedly reverses its direction.

Cable Two or three insulated wires surrounded by an outer layer of rubber or flexible plastic.

Circuit breaker An electromagnetic switch that opens and cuts the current off if too much current passes through it.

Conservation of energy Energy cannot be created or destroyed.

Coulomb (C) The unit of electrical charge, equal to the charge passing a point in a (direct current) circuit in 1 second when the current is 1 A.

Direct Current Electric current in a circuit that is in one direction only.

Efficiency Useful energy transferred by a device / total energy supplied to the device.

Electric current Flow of electric charge. The size of an electric current (in amperes, A) is the rate of flow of charge.

Electrical energy Energy transferred by the movement of electrical charge.

Electromagnetic induction

The process of inducing a potential difference in a wire by moving the wire so it cuts across the lines of force of a magnetic field.

Field line See magnetic field line.

Force A force can change the motion of an object (in newtons, N).

Frequency of an alternating current

The number of complete cycles of oscillation per second, equal to 1/the time period. The unit of frequency is the hertz (Hz).

Line of force See magnetic field line.

Magnetic field line Line in a magnetic field along which a magnetic compass points; also called a magnetic field line or field line.

Magnetic poles Ends of a bar magnet or a magnetic compass.

Motor effectWhen a current is passed along a wire in a magnetic field and the wire is not parallel to the lines of the magnetic field, a force is exerted on the wire by the magnetic field.


National Grid The network of cables and transformers used to transfer electricity from power stations to consumers (i.e. homes, shops, offices, factories, etc.).

North pole North pointing end of a freely suspended bar magnet or of a magnetic compass.

Potential differenceA measure of the work done or energy transferred to the lamp by each coulomb of charge that passes through it. The unit of potential difference is the volt (V).

Power The energy transformed or transferred per second. The unit of power is the watt (W).

South pole South-pointing end of a freely suspended bar magnet or of a magnetic compass.

Split-ring commutator Metal contacts on the coil of a direct current motor that connects the rotating coil continuously to its electrical power supply.

Step-down transformer Electrical device that is used to step down the size of an alternating voltage.

Step-up transformer Electrical device that is used to step up the size of an alternating voltage.

Switch mode transformer

A transformer that works at much higher frequencies than a traditional transformer. It has a ferrite core instead of an iron core.

Transformer Electrical device used to change an (alternating) voltage. See also Step-up transformer and Step-down transformer.

Volt (V) The unit of potential difference, equal to energy transfer per unit charge in joules per coulomb.

Wasted Energy Energy that is not usefully transferred.

Watt (W) The unit of power.


Electromagnets Exam Questions1. The diagram below shows a door lock which can be opened from a flat inside a building.

(a) Explain how the door is unlocked when the switch is closed.

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(b) State two changes which would increase the strength of the electromagnet.

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

2 ..................................................................................................................................(2)

(c) Why is the spring needed in the lock?

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....................................................................................................................................(1)


(d) The connections to the coil were accidentally reversed. Would the lock still work?

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

Explain your answer.

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....................................................................................................................................(2)

(Total 9 marks)

2. Circuit breakers help to make the electricity supply in homes safer.A circuit breaker is an automatic safety switch. It cuts off the current if it gets too big.

+ +

– –E lec tro -m a g n e t

E lec tro -m a g n e t

Iro n b o lt Iro n b o lt

S w itchis O N

S w itc his O F F

S p rin g

S p rin g

P las ticp lu n g e r

P la s ticp lu n g e r

R e-se tb u tto n

R e -se tb u tto n

To h o u sec irc u itap p lia n c es

Describe, in as much detail as you can, how this circuit breaker works.

To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words.

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3. The diagram shows a switch that is operated by an electromagnet.

E lec tro m ag n e t

P iv o t

I ro n a rm

C o n tac ts

(i) What is this type of switch called?

..........................................................................................................................(1)

(ii) The switch is used in a car starter motor circuit.

M

Ig n itio nk ey

Sta rte r m o to r

Explain how turning the ignition key makes a current flow in the starter motor. The explanation has been started for you.

When the ignition key is turned ......................................................................

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

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(Total 4 marks)


Electromagnets Exam Questions Mark Scheme1. (a) current flows4coil / core magnetised / electromagnet activated / energised / turned onattracts iron barcausing

bolt to be pulled outeach for 1 mark

(b) more turns 2bigger current / e.m.fsofter iron coreany two for 1 mark each

(c) to relock door / return iron bar / to lock door 1for 1 mark

(d) iron bar would still be attracted / coil still magnetised so still works 2for 1 mark each

yes + wrong answer0 marks

yes + current still flows1 mark

yes + still magnetised / iron bar still attracted2 marks

2. Quality of written communication: One mark for correct sequencing.1bolt out → plunger up → switch off / circuit brokenany five from 5

high current flows electromagnet is stronger the iron bolt is pulled out the plastic plunger moves up the switch is lifted / open / offaccept circuit is broken no current flowing to re-set the plunger must bepushed down3. (i) relay 1

accept solenoiddo not accept magnetic switch

(ii) a current flows through the coil (of the electromagnet)1or a current flows through the electromagnetor a (magnetic) field is produced

accept ‘electricity’ for ‘current’accept the electromagnet is activated or magnetised or turned ondo not accept answer in terms of magnetic charge

the (iron) arm is attracted to the electromagnet 1accept the arm pivots or moves towards the electromagnet

the contacts are pushed together 1do not accept contacts attract

[4]


The Motor Effect Exam Questions1. The diagram shows a simple electric motor.

The coil rotates as shown in the diagram.

(a) State two ways of reversing the direction of forces F1 and F2.

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

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

.....................................................................................................................................(2)

(b) Give two ways in which the size of the forces can be increased.

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

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

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

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(Total 4 marks)


2. (a) The diagram shows one way of demonstrating a particular electrical effect.

N S

As the wire is moved downwards between the poles of the magnet the ammeter needle swings to the right.

(i) What name is given to this electrical effect?

...........................................................................................................................(1)

(ii) What happens to the ammeter needle when the wire is moved upwards between the poles of the magnet?

...........................................................................................................................(1)

(iii) When the wire is held stationary between the poles of the magnet the ammeter needle does not move. Explain why.

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(b) Complete the following sketch graph to show one complete cycle of an alternating current.

C u rren t

T im e

(1)(Total 5 marks)


3. The diagram shows apparatus used to demonstrate the electric motor effect. When he switch is closed the wire moves.

M o v ab le w ire

M e ta l ra il

M e ta l ra il

(i) Draw an arrow on the diagram to show the direction the wire moves.(1)

(ii) Explain why the wire moves.

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.....................................................................................................................................(2)

(Total 3 marks)

4. The diagram shows apparatus used to demonstrate the motor effect. X is a short length of bare copper wire resting on two other wires.

Bare copper wire (X)

Bare copperwire

Switch

Horseshoemagnet

Power supply

Black

Red+

–

(a) (i) Describe what happens to wire X when the current is switched on.

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(ii) What difference do you notice if the following changes are made?

A The magnetic field is reversed.

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B The current is increased.

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(b) The diagram shows a coil placed between the poles of a magnet. The arrows on the sides of the coil itself show the direction of the conventional current.

F

FN S

Magnet

Coil Pivot

The arrows labelled F show the direction of the forces acting on the sides of the coil. Describe the motion of the coil until it comes to rest.

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(c) Most electric motors use electromagnets instead of permanent magnets. State three of the features of an electromagnet which control the strength of the magnetic field obtained.

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

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

3 ................................................................................................................................(3)

(Total 9 marks)


5. The diagram below shows a rectangular coil of wire between the poles of a magnet.The two ends of the coil make contact with two slip rings.The slip rings are connected at points X and Y to a centre-zero meter.

(a) (i) Describe what happens to the meter needle if the coil is rotated in the magnetic field.

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...........................................................................................................................(2)

(ii) Explain your answer.

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(b) The meter is now removed from the circuit.The contacts at X and Y are then connected to the inputs of a cathode ray oscilloscope.

The grid below shows the trace on the oscilloscope when the coil is rotated at a steady rate in the magnetic field.

The speed of rotation of the coil is now doubled.

On the grid below sketch the trace which you would expect to see on the oscilloscope screen.The controls of the oscilloscope have not been changed.

(3)(Total 7 marks)

6. (a) The diagram shows a loop of wire which is being moved rapidly down between the poles of a magnet.


m A

0

What will be the reading on the milliammeter as the loop of wire moves down?

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

Give a reason for your answer.

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....................................................................................................................................(2)


(b) The diagram shows one way of measuring the rate of flow of fluid through a pipe.

Explain how the flow of fluid through the pipe causes an alternating current to be induced in the solenoid.

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(c) The graph shows how the milliammeter reading changes with time when a fluid flows at a steady rate through the pipe.

C u rren t inm illia m p s

T im e in m illiseco n d s

2 0

1 5

1 0

5

0

– 5

– 1 0

– 1 5

– 2 00 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0

Draw on the grid below, a graph to show how the milliammeter reading would change if the fluid flow is increased, so that the turbine rotates twice as fast.

C u rren t inm illia m p s

T im e in m illiseco n d s

2 0

1 5

1 0

5

0

– 5

– 1 0

– 1 5

– 2 00 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0

(2)(Total 7 marks)


Motor Effect Exam Questions Mark Scheme1. (a) reverse the current 1reverse the magnetic field 1

accept swap the magnets over(b) increase the strength of the magnetic field 1

accept use stronger magnets do not accept use bigger magnetsincrease the size of the current 1

2. (a) (i) (electromagnetic) induction 1accept inducing current

(ii) swings to the left 1accept moves to left or moves the other wayaccept it will go to – 1do not accept moves back to zero

(iii) no (induced) current when 1accept no (induced) voltage

no (relative) movement between conductor and magnetic field 1do not accept wire not movingaccept ‘field’ or ‘magnet’ for ‘magnetic field’accept no change of flux linkageaccept conductor or wire not cutting the fieldaccept no change in magnetic field around wiredo not accept field not broken

(b) one complete cycle shown 1curve should be regulardo not accept more than one cycle

accept good sawtooth or square wave

3. (i) away from magnet 1arrow should be perpendicular to field lines and current as judged by eye

(ii) current in wire creates magnetic field around wire 1two fields interact or combine giving a resultant force (on the wire) 1

[3]

4. (a) (i) it moves or experiences a force horizontally to the right 1for 1 mark

(ii) A - moves in opposite direction or force reversed e.c.f. 2B - faster movement or larger force(not move further)

for 1 mark each(b) turns clockwise3oscillates/reversescomes to rest facing field/at 90o to field/vertically

for 1 mark each(c) number of turns or linear number density of turns 3currentcore

for 1 mark each

5. (a) (i) the ammeter needle will deflect/will register a reading/will 2move from zero positionthe deflection of the ammeter reading will be repeatedly to and fro/will keep changing direction

for 1 mark each(ii) the moving coil of wire cuts through/across the magnetic 2field/flux/lines of force

the direction of movement of the opposite sides of the coil reverses every half cycle/revolutionfor 1 mark each

(b) twice the frequency/half the wavelength 3(i.e. two and half cycles shown)for 2 marks

else greater frequency/more cycles/shorter “wavelength”for 1 mark

greater amplitude/heightfor 1 mark


6. (a) zero 1not it stays the same

(induced) currents or (induced) 1voltages on either side of loop opposeaccept generated currents generated voltagesnot wire moves out of field

(b) magnets turn or rotate or spin or 1movegiving (relative) movement between 1magnetic (field) and solenoid

accept coilfield linkage increases then decreases 1i.e. a.c.

accept answer in terms of pushing a magnet into and pulling a magnet out of a solenoidaccept field changesi.e.1st mark − magnets moving2nd mark − field/magnet interacts with coil

3rd mark − the interaction is changing


Electromagnetic Induction Exam Questions1. The equipment shown was used to produce the trace on the computer screen.

Describe and explain what was done with the equipment to produce this trace.

To gain full marks for this question, you should write your ideas in good English. Put them in a sensible order and use the correct scientific words.

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

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

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

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

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

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

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

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

...............................................................................................................................................(Total 4 marks)

2. (a) The diagram shows a magnet being moved into a coil of wire.

The reading on the meter is shown in the diagram.

–0

+N S


Draw on the diagram the meter reading that you would expect to get in each of the following cases.

(i) The magnet is at rest inside the coil.

–0

+N S

(1)

(ii) The magnet is moved out of coil.

–0

+N S

(1)


To gain full marks in this question you should write your ideas in good English. Put them into a sensible order and use the correct scientific words.

(b) The diagram below shows a bicycle dynamo and part of the wheel.

N S

Ty re

M ag n e t

W ires to lam pC o il o n so ft-iro n co re

Explain, as fully as you can, why a current flows through the bicycle lamp when the wheel of the bicycle turns.

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

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

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

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

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

....................................................................................................................................(4)

(Total 6 marks)


Electromagnetic Induction Exam Questions Mark Scheme

1. Quality of written communication: 11 mark for correct sequencing magnet in produces voltage / current→ magnet out produces voltage /current → in opposite directionany three from: 3magnet moved to coil / coilmoved to magnetproduces a current / voltagecorrect reference to induction magnet moved from coil / coil moved from magnetproduces current / voltage

correct reference to reversal of current / voltage

2. (a) (i) pointer at 0 1(ii) pointer to left of 0 1Quality of Written CommunicationThe answer to this part of the question requires ideas in good English, in a sensible order with correct use of scientific terms. Quality of writtencommunication should be considered in crediting points in the mark scheme.

Max. 3 if ideas not well expressed.(b) magnet turns 1

changing magnetic field in coil or core 1so induces a voltage 1

causing a current to flow 1


Transformers Exam Questions1. The outline diagram below shows part of the National Grid. At X the transformer increases the voltage to

a very high value. At Y the voltage is reduced to 240 V for use by consumers.

P ow er station Transform er Transform erX Y

(i) The frequency of the mains supply to houses is 50 Hz. Explain what this means.

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

.....................................................................................................................................(2)

(ii) At X a transformer increases the voltage. What happens to the current as the voltage is increased?

.....................................................................................................................................(1)

(iii) Why is electrical energy transmitted at very high voltages?

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

.....................................................................................................................................(1)

(iv) The transformer at Y reduces the voltage before it is supplied to houses. Why is this done?

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

.....................................................................................................................................(1)

(Total 5 marks)


2. The drawing shows an experiment using a low voltage supply, a joulemeter, a small immersion heater and a container filled with water.

The immersion heater is designed for use in a tropical fish tank. It is connected to a step-down transformer supplied by 230 V a.c. mains.

The inside of a step-down transformer consists of three main parts. Name the three parts and briefly describe them. You may add to the diagram to help you to answer.

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

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

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

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

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

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

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

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

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


(Total 4 marks)


3. (a) The drawing shows a small transformer used to recharge the battery in a 4.2 V mobile phone from a 230 V mains supply.

Explain how you know that this is a step-down transformer.

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

.....................................................................................................................................(1)

(b) A transformer consists of an insulated coil of wire, called the primary coil, on one side of a core. Another coil of insulated wire, called the secondary coil, is on the other side.

Give two features of the core.

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

2 ..................................................................................................................................(2)


(c) Electricity is transmitted for long distances at voltages of 400 kV.

Explain one advantage and one disadvantage of using such high voltages.

Advantage .................................................................................................................

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

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

.....................................................................................................................................(2)

Disadvantage .............................................................................................................

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

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

.....................................................................................................................................(2)

(d) What charge, measured in coulombs (C), is passed when a voltage of 400 kilovolts (kV) transfers 200 megajoules (MJ) of energy?

voltage = chargeenergy

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

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

Charge = .................................................... C(3)

(Total 10 marks)

4. (a) Electrical energy is distributed around the country by a network of high voltage transmission cables.

P o w ersta tio n

T ran sfo rm er Tran sfo rm er

A

Tran sm iss io n

C ab lesC o n su m er


(i) For the system to work the power is generated and distributed using alternating current rather than direct current. Why?

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

...........................................................................................................................(1)

(ii) Transformers are an essential part of the distribution system. Explain why.

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

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

...........................................................................................................................(2)

(b) The power station generates 100 MW of power at a voltage of 25 kV. Transformer A, which links the power station to the transmission cables, has 44 000 turns in its 275 kV secondary coil.

(i) Write down the equation which links the number of turns in each transformer coil to the voltage across each transformer coil.

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

...........................................................................................................................(1)

(ii) Calculate the number of turns in the primary coil of transformer A. Show clearly how you work out your answer.

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

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

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

Number of turns = .......................(2)

(Total 6 marks)


Transformers Exam Questions Mark Scheme1. (i) current reverses; 250 × each second (100?)

for 1 mark each(ii) reduces 1

for 1 mark(iii) less heat/energy/power wasted 1(in power lines)

for 1 mark(iv) for safety 1

for 1 mark

2.each mark may be gained from a written description or from a caption on the diagram or from both together but do not credit if there is any contradiction between them

one coil on each side 1of insulated wire 1

or insulated coilnumber of turns on primary coil/1coil 1/input coil greater than number ofturns on the secondary coil/coil 2/output coil

this must be clear for example do not credit more coils do not credit bigger coilcore of laminated iron 1

or core of (soft) iron

3. (a) output voltage less than (the) input voltage 1or p.d. across output less that p.d.across input or output is (only) 4.2 V (whereas) the input is 230Vor WTTE (words to that effect)

(b) any two from 2(made of soft) ironlaminated

or designed to reduce eddy currentsor made of thin slices with slices of insulating material between them

core(s) joined to make a ring(c) ADVANTAGE 2

any two fromcurrent will be (relatively) low(er)power / heat / energy losses will be low(er)(so) more efficient

do not credit cheaper


DISADVANTAGEEITHERdifficult to insulate 1(so) difficult to prevent discharge to earth 1

or (hence) pylons have to be tall (accept big)or (hence) pylons are expensiveor (so) danger of (lethal electric)shock(s)do not credit dangerous or expensive

ORdifficult to switch 1(so) arcing problems 1ORtransformers (required) 1step-up (transformers at the supply end) and step-down 1(transformers at the demand end)

candidate does not have to specify butdo not credit if candidate specifiesincorrectlyor transformers are expensive

(d) EITHER500 (C) 3

accept 0.5 (c) (1) mark 3ORcharge = energy ÷ voltage 1(charge =)200 000 000 ÷ 400 000 1

[10]4. (a) (i) transformers only work with ac. 1

(ii) used to increase or decrease or 1change voltage or currentreducing the energy or heat or1power loss (along the cables)or reduce to safe domestic level

must be consistent with first answer(b) (i) voltage across primary = no of turns in primary 1

voltage across secondary no of turns in secondaryaccept = or=

(ii) NP = 4000 2=for 1 mark


Transformers in Action Exam Questions1. The diagram below shows a transformer.

2 4 0 Va .c .

in p u t

p rim aryco il

seco n d a ryco il

V

(i) Name the material used to make the core of the transformer.

.....................................................................................................................................(1)

(ii) The primary coil has 48 000 turns and the secondary coil 4000 turns.

If the input voltage is 240 V a.c., calculate the output voltage.

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

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

Answer ......................................... V(2)

(iii) Explain how the use of such a transformer could be adapted to transform a low voltage into a higher voltage.

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

.....................................................................................................................................(1)

(Total 4 marks)


2. (a) An appliance in a house has a transformer. The transformer is used to reduce the voltage to the level needed by the appliance.

The diagram shows the transformer.

1 0 0 0 0 tu rn s

2 4 0 V a .c .

2 0 0 0 tu rn s

(i) Name the material used for the core of the transformer.

...........................................................................................................................(1)


(ii) The transformer has 10 000 turns on the input side and 2000 turns on the output side. If the mains voltage of 240 volts is applied to the input, calculate the output voltage. You may find the following information helpful:

o u tp u t v o lta g e

in p u t v o lta g e=

n u m b e r o f tu rn s o n o u tp u t c o i l

n u m b e r o f tu rn s o n in p u t c o i l

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

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

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

...........................................................................................................................(3)

(b) Explain, in terms of magnetic fields, how a transformer works.

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

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

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

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

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

.....................................................................................................................................(4)

(c) A 12 V car battery is connected to the input leads of the transformer. It is hoped to reduce the voltage to 2.4 V in order to run a small motor. When the output voltage is measured it is found to be zero.

Explain why the output voltage is zero.

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

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

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

.....................................................................................................................................(2)

(Total 10 marks)

3. Diagram 1 shows a magnet being moved into a coil. Diagram 2 shows a magnet stationary in a coil. Diagram 3 shows a magnet being moved out of a coil.


The meter looks like this when no current is flowing.

(a) The position of the meter pointer has been drawn on diagram 1.Draw the positions of the meter pointer on diagrams 2 and 3.

D ia g ram 1

C e n tre 0m eter

C o il o f w ire

M ag n et m o v in gin to co il

S

N

D ia g ram 2

C e n tre 0m eter

C o il o f w ire

S

N

M ag n et s ta tio n aryin co il

D ia g ram 3

C e n tre 0m eter

C o il o f w ire

M ag n et m o v in go u t o f co il

N

(2)

(b) Bicycle dynamos generate electricity by rotating a magnet inside a coil of wire.

Give two ways of increasing the voltage produced by this kind of generator.

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

2 ..................................................................................................................................(2)


(Total 4 marks)

4. (a) The diagram represents a simple transformer used to light a 12 V lamp. When the power supply is switched on the lamp is very dim.

L a m in a te d iro n c o re

P rim aryc oil

S e co n d aryc o il

a . c .in p u t 1 2 V

(i) Give one way to increase the voltage at the lamp without changing the power supply.

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

............................................................................................................................(1)


5. (a) The diagram shows a simple step-up transformer. It is designed to light a 6 V lamp using a 1.5 V power supply.

1 .5 V p rim ary(in p u t)

P r im ary(in p u t)

co il

S e co n d ary(o u tp u t)

co il

C o re

6 V

(i) Which one of the following power supplies should be used?

Draw a ring around your answer.

(1)

(ii) Which one of the following metals is used to make the core of the transformer?

Draw a ring around your answer.

aluminium copper iron steel(1)

(iii) Complete this sentence by crossing out the two lines in the box that are wrong. If there are 20 turns of wire on the primary (input) coil, there will be

less than 20 exactly 20 more than 20

turns of wire on the secondary (output) coil.

(1)

(b) The graph shows how the potential difference across the secondary (output) coil of a transformer AQA GCSE Physics P3.3 Scheme of Work: Keeping Things Moving T. Baylis

changes as the potential difference across the primary (input) coil is changed.

1 2 .0

1 0 .0

8 .0

6 .0

4 .0

2 .0

0 .00 .0 1 .0 2 .0 3 .0 4 .0

P o ten tia l d iffe re n ce ac ro ss th ep rim ary (in p u t) c o il in v o lts

P o ten tia ld iffe ren ceacro ss th eseco n d a ry

(o u tp u t) co ilin v o lts

How does the graph show that the transformer is a step-up transformer?

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

...............................................................................................................................................(1)

(c) The diagram shows how the National Grid transmits electrical energy over long distances.

Complete the sentences by choosing the correct word or phrase from the box. Each word or phrase may be used once or not at all.

current less more potential difference resistance

The step-up transformer increases the ...........................................................at which the

electrical energy is transmitted through the cables. The transformer also reduces the

....................................... in the cables. This makes the whole system......................

efficient.(3)

(Total 7 marks)

(ii) What is meant by the iron core being laminated?


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

............................................................................................................................(1)

(b) Electrical energy is distributed around the country by a network of high voltage cables.

P o w ersta tio n

T ran sfo rm er Tran sfo rm er

A

Tran sm iss io n

C ab lesC o n su m er

(i) For the system to work the power is generated and distributed using alternating current rather than direct current. Why?

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

............................................................................................................................(1)

(ii) Transformers are an essential part of the distribution system. Explain why.

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

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

............................................................................................................................(2)

(iii) The transmission cables are suspended high above the ground. Why?

............................................................................................................................(1)

(c) The power station generates 100 MW of power at a voltage of 25 kV. Transformer A, which links the power station to the transmission cables, has 44 000 turns in its 275 kV secondary coil.

(i) Write down the equation which links the number of turns in each transformer coil to the voltage across each transformer coil.

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

............................................................................................................................(1)

(ii) Calculate the number of turns in the primary coil of transformer A. Show clearly how you work out your answer.

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

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

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

Number of turns = ........................................(2)


(d) The diagram shows how the cost of transmitting the electricity along the cables depends upon the thickness of the cable.

C os t o f b u y in g an din sta llin g th e cab le

C o st d u e to h ea tin glo sses in th e ca b le

T h ick n ess o f ca b le

C o s t

(i) Why does the cost due to the heating losses go down as the cable is made thicker?

............................................................................................................................(1)

(ii) By what process is most heat energy lost from the cables?

............................................................................................................................(1)

(Total 11 marks)

6. (a) The diagram shows a simple step-up transformer. It is designed to light a 6 V lamp using a 1.5 V power supply.


(i) How can you tell from the diagram that this is a step-up transformer?

...........................................................................................................................(1)

(ii) Which material is used to make the core of a transformer?

...........................................................................................................................(1)

(iii) State two ways in which the design of the transformer could be changed to reduce the brightness of the lamp.

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

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

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

...........................................................................................................................(2)


(b) Chris investigates three different transformers. For each transformer Chris changes the potential difference across the primary (input) coil and measures the potential difference across the secondary (output) coil.

The results for each transformer are given in the graph.

6 .0

5 .0

4 .0

3 .0

2 .0

1 .0

0 .00 .5 1 .0 1 .5 2 .0 2 .5 3 .00 .0

J K

L

P o ten tia l d iffe ren ce ac ro ss th ep rim a ry (in p u t) co il in v o lts

P o ten tia ld iffe ren c ea cro ss th esec o n d a ry

(o u tp u t) co ilin v o lts

Which of the transformers, J, K or L, is working as a step-down transformer?

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

Give a reason for your answer.

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

.....................................................................................................................................(2)

(c) The diagram shows how the National Grid transmits electrical energy over long distances.

(i) Why do the power stations generate a.c. and not d.c?

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

...........................................................................................................................(1)


(ii) State the purpose of transformer A and explain why it is an essential part of the National Grid system.

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

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

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

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

...........................................................................................................................(3)

(Total 10 marks)

7. The diagram shows Sue’s design for a simple wind speed gauge.


(a) Explain why the wind causes the a.c. voltmeter to give a reading. The explanation has been started for you.

The wind causes the plastic cups to turn. This causes the spindle and ......................

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

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

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

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

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

.....................................................................................................................................(3)

(b) Why does the voltmeter reading increase as the wind speed increases?

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

.....................................................................................................................................(1)

(c) The gauge is not sensitive enough to measure light winds.

Give one way that Sue can modify the design to make the gauge more sensitive.

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

.....................................................................................................................................(1)

(d) How could Sue make the gauge monitor and record wind speed automatically?

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

.....................................................................................................................................(1)

(Total 6 marks)


Transformers in Action Exam Questions Mark Scheme1. (i) iron 1

for 1 mark(ii) 20 2

gains 2 markselse working

gains 1 mark(iii) reverse input/output 1

for 1 markor increase secondary turns

2. (a) (i) Iron 1for 1 mark

(ii) V/240 = 2000/10 000 3V = 48Vfor 1 mark each

(b) changing current in primary4causes changing (magnetic) field in corelinks to secondaryinducing voltage (emf) in secondary (NOT current)secondary voltage/current is alternating

for 1 mark each5. (a)needle at 0 1

needle to left of 0 1(b) any two from 2

increase speed / pedal fasterincrease strength of magnetincrease number of turns on coil /number of coilsincrease area of coil

(c) magnetic field not changing/no electromagnetic induction 2because direct current for 1 mark each

3. (a) (i) one of the following: 1• increase number of turns on the secondary coil• decrease number of turns on the primary coil

(ii) constructed in (thin) layers 1(b) (i) transformers only work with a c 1

(ii) used to increase or decrease or change voltage or current 1reducing the energy or heat or power loss (along the cables)or reduce to safe domestic level 1

must be consistent with first answer(iii) (several metres of) air gives good electrical 1insulation (between cables and earth) or reduce chance of earthing or sparks or arcing or to avoid people touching it

4. (a) (i) B 1(ii) iron 1(iii) more than 20 1

(b) pd across secondary is (always) bigger than pd across primary coil 1accept voltage for pd


(c) potential difference 1current 1more 1

5. (a) (i) more turns / coils on the secondary than primary 1accept output for secondaryaccept input for primaryaccept converse

(ii) iron 1(iii) decrease number turns on secondary 1increase number turns on primary 1

do not accept reduce voltage of power supply(b) L 1

pd across secondary is smaller than pd across primary 1accept voltage for pd

(c) (i) transformers only work with a.c. 1accept converseaccept transmission system would be very inefficient if d.c. used

(ii) to increase the pd at which the energy is transmitted 1any two from: 2energy / power losses (from cables) are much lowerreduces current in cablescables heat up less

efficiency of system increases

6. (a) magnet to turn 1magnetic field cut by the coil 1orrotating magnetic field links with the coil

accept magnetic field links with coilaccept voltage for pd potential difference induced across coil 1

(b) any one from: 1• speed of rotation of magnet increases• magnetic field lines cut at a faster rate• rate of change of flux linkage increases

(c) any one from: 1• increase number of turns on coil • use stronger magnet • use larger cups • use more cups • use a millivoltmeter

(d) any one from: 1• replace the voltmeter with a datalogger• connect voltmeter to a computer

• record output with a computer


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