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P3 11 Transformers Exam Questions
188 minutes
186 marks
Q1. (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.
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(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.
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2 ..................................................................................................................................(2)
(Total 3 marks)
Q2. 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.
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Q3. (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.
(i) Name the material used for the core of the transformer.
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(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:
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(b) Explain, in terms of magnetic fields, how a transformer works.
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(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.
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(Total 10 marks)
Q4. The diagram below shows a transformer.
(i) Name the material used to make the core of the transformer.
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(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.
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Answer ......................................... V(2)
(iii) Explain how the use of such a transformer could be adapted to transform a low voltage into a higher voltage.
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(Total 4 marks)
Q5. (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.
(i) Give one way to increase the voltage at the lamp without changing the power supply.
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(ii) What is meant by the iron core being laminated?
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(b) Electrical energy is distributed around the country by a network of high voltage cables.
(i) For the system to work the power is generated and distributed using alternating current rather than direct current. Why?
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(ii) Transformers are an essential part of the distribution system. Explain why.
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(iii) The transmission cables are suspended high above the ground. Why?
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(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.
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(ii) Calculate the number of turns in the primary coil of transformer A. Show clearly how you work out your answer.
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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.
(i) Why does the cost due to the heating losses go down as the cable is made thicker?
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(ii) By what process is most heat energy lost from the cables?
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(Total 11 marks)
Q6. A transformer is used to reduce the 230 V a.c. mains to the 12 V supply required for the lighting system. The transformer has 1150 turns on its primary coil.
(i) Write down the equation which links the number of turns of each transformer coil to the voltage across each transformer coil.
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(ii) Calculate the number of turns on the secondary coil of the transformer. Show clearly how you work out your answer.
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number of turns on the secondary coil = .........................(2)
(Total 3 marks)
Q7. (a) This notice is on the back of a television set.
The transformer used in the television set has 75 turns on its primary coil. The potential difference (p.d.) across the primary coil is 230 volts and the p.d. across the secondary coil is 32 200 volts.
Use the equation below to calculate the number of turns on the secondary coil.
Show clearly how you work out your answer.
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Number of turns on the secondary coil = ....................(2)
(b) The diagram shows the structure of a transformer.
Explain how the transformer works.
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(Total 5 marks)
Q8. The diagram shows the design for a remotely controlled door bolt.
When the correct numbers are entered into the keypad the transformer switches on. Then the door can be opened.
(a) What kind of transformer is shown in the diagram?
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(b) What does the abbreviation a.c. stand for?
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(c) Complete the sentences using the correct words from the box.
attracts downwards magnet reflects repels
sideways switch transformer upwards
(i) When a current flows in the coil, the coil becomes a ................................... .
(ii) The coil ................................... the iron bolt which moves ............................(3)
(Total 5 marks)
Q9. (a) The diagram shows a transformer.
(i) Is the transformer in the diagram being used as a step-up transformer or as a step-down transformer?
Put a tick ( ) in the box next to your answer.
a step-up transformer
a step-down transformer
Explain your answer.
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(ii) Why is insulated wire, and not uninsulated wire, used to make the coils?
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(iii) Why is the core made of iron?
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(b) A transformer has 500 turns on its primary coil and 7500 turns on its secondary coil. The potential difference across the primary coil is 150 volts.
Use the equation in the box to calculate the potential difference across the secondary coil.
Show clearly how you work out your answer.
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Potential difference across the secondary coil = .............................. volts(2)
(c) Step-down transformers are used between power lines and people’s houses.
Explain why.
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(d) Before 1926, large towns had their own local power stations. After 1926, these power stations were connected to form the National Grid.
Explain the advantage of having a National Grid system.
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(Total 9 marks)
Q10. (a) The diagram shows a transformer.
(i) What is part A?
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(ii) What is part B and what is it made of?
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(iii) When there is an alternating current in the primary coil, what is produced in part B?
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(b) Transformers are used in the National Grid. The diagram shows part of the National Grid.
Complete the two spaces in the sentence.
Transformer C is a ............................................. transformer and transformer D is
a ............................................. transformer.(1)
(c) This is an item from a newspaper.
Which two suggestions would reduce the possible risk to people’s health?Put a tick ( ) in the box next to your answers.
Do not build new houses near to existing power lines.
Move the power lines so that they take the shortest routes.
Move each power station to the centre of the nearest city.
Build new power lines away from where people live.
Use more transformers in the National Grid. (2)
(Total 8 marks)
Q11. (a) The basic structure of a transformer is a primary coil of insulated wire, an iron core and a secondary coil of insulated wire.
(i) Why is the core made of iron?
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(ii) Explain how a transformer works.
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(b) A small step-down transformer is used in the charger for an electric screwdriver.
The input to the transformer is 230 V a.c. mains supply and the output is 5.75 V a.c.There are 3200 turns on the primary coil.
Use the equation in the box to calculate the number of turns on the transformer’s secondary coil.
Show clearly how you work out your answer.
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Number of turns = ..............................(2)
(Total 7 marks)
Q12.(a) The diagram shows the basic structure of a mains-operated transformer.
(i) Complete the labelling of the coils by adding a word to each of the dotted lines.(2)
(ii) In the transformer shown in the diagram, the potential difference across the input is 20 V, a.c. The potential difference across the output coil is 40 V, a.c.
What type of transformer is this?
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(1)
(b) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate.
A current flowing in a coil produces a magnetic field in the core.
Explain how an alternating input can produce an alternating output of a higher potential difference.
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(c) The transformer inside a USB adapter is a switch-mode transformer.
Apart from size, state one other difference between a switch-mode transformer and a traditional mains-operated transformer.
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(Total 10 marks)
Q13. The diagram shows the basic structure of a transformer.
(a) Explain how a transformer works.
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(b) A transformer is used to change the 230 volt mains electricity supply to the 12 volts needed to operate a low voltage halogen lamp. The current through the halogen lamp is 4 amps.
Calculate the current drawn by the transformer from the mains electricity supply.
Assume that the transformer is 100 % efficient.
Write down the equation you use, and then show clearly how you work out your answer.
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Current = ........................................... amps(2)
(Total 7 marks)
Q14. The diagram shows a transformer made by a student. The student has designed the transformer to make a 6 V light bulb work using a 2 V power supply.
(a) Draw a ring around the correct answer to complete the following sentences.
(i) For the transformer to work, the student
must use an a.c.
can use either an a.c or a d.c.
must use a d.c.
power supply.(1)
(ii) On the primary coil there are 30 turns of wire. For the lamp to work brightly
less than 30
exactly 30
more than 30
there must be turns of wire on the secondary coil.
(1)
(b) What is the transformer core made from?
Give a reason for your answer.
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(Total 4 marks)
Q15. The diagram shows a USB power adapter which plugs into a 230 V a.c. mains socket.
The adapter contains a small step-down transformer.
(a) The core of the transformer is made of laminated soft iron.
Why is iron used?
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(b) The coils of the transformers are made of insulated copper wire.
Why is the wire insulated?
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(c) There are 500 turns on one coil of the transformer and 20 000 turns on the other coil.
Use the equation in the box to calculate the p.d. across the secondary coil.
Show clearly how you work out your answer and give the unit.
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p.d. across the secondary = ..............................................................
(3)(Total 5 marks)
Q16. A teacher demonstrates a small transformer.
(a) (i) What is the core made of?
Draw a ring around the correct word in the box.
aluminium copper iron(1)
(ii) The potential difference (p.d.) across the secondary coil is less than the p.d. across the primary coil.
What sort of transformer is it?
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(b) Where is a step-up transformer used as part of the National Grid?
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(c) The teacher writes a note about the transformer but leaves five spaces.
Use the correct words from the box to complete the spaces.
coil core current ends field wire
A transformer works because an alternating ........................................ in the
primary .................................................. produces a changing magnetic
....................................... in the .......................................... and then in the
secondary coil.
This induces an alternating potential difference across the ......................
of the secondary coil.(5)
(Total 8 marks)
Q17. (a) The diagram shows the basic structure of a step-up transformer.
(i) What is the core made of?
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(ii) Explain how an alternating input produces an alternating output.
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(b) Fly killers are used in kitchens and food stores because flying insects carry diseases which cause food poisoning.
The diagram shows the inside of one design. Insects are attracted to a fluorescent lamp.
The metal grids have a high potential difference (p.d.) between them. The insects are killed as they fly between the grids.
A transformer is used in the fly killer. There is a p.d. of 230 V across the primary coil. There are 300 turns of wire on the primary coil and 4000 turns on the secondary coil.
Use the equation in the box to calculate the p.d. across the secondary coil.
Show clearly how you work out your answer.
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Potential difference = ............................................................V(3)
(Total 7 marks)
Q18. (a) In the National Grid, very large step-up transformers link power stations to the transmission cables.
A transformer used for this purpose has 800 turns on its primary coil and 12 800 turns on
its secondary coil. The p.d. (potential difference) across its primary coil is 25 kV.
Use the equation in the box to calculate the p.d. across its secondary coil.
Show clearly how you work out your answer and give the unit.
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p.d. across secondary coil = .......................................................(3)
(b) The primary and secondary coils of a transformer are made of insulated wire.
Why is this insulation necessary?
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(c) Describe what happens when an alternating potential difference is applied across the primary coil of a transformer.
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(Total 7 marks)
Q19. (a) The drawing shows the plug for operating a radio from the mains.
This plug contains a transformer. There are 4600 turns on its primary coil and 200 turns on its secondary coil. The plug is used on the mains supply and has a potential difference (p.d.) of 230 V across its primary coil.
Use the equation in the box to calculate the p.d. across the secondary coil of the transformer.
Show clearly how you work out your answer.
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p.d. across secondary = ................................... V(2)
(b) The coils of the transformer are made of insulated wire.
Why is the wire insulated?
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(c) (i) What material is the core of a transformer made from?
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(ii) Why is the core made from this material?
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(Total 5 marks)
Q20. The diagram shows part of the system used to supply a farm with electricity.
(a) The core of the transformer is made of metal.
Complete the following sentence by drawing a ring around the correct word in the box.
copper.
The metal used for the core of the transformer is iron.
steel.
(1)
(b) (i) What sort of transformer is shown in the diagram?
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(ii) Complete the following sentence by drawing a ring around the correct line in the box.
In this transformer, the number of turns on the secondary coil is
less than
the same as
the number of turns on the primary coil.
greater than
(1)
(c) Transformers and other electrical equipment can be dangerous.
The following bar chart shows the numbers of children, aged 14 or under, killed or injured in electrical accidents in the UK in 2000, 2001 and 2002.
(i) In which of these years were most children killed or injured in electrical accidents?
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(ii) A newspaper claims that the number of children killed or injured by electrical accidents will increase in 2011.
Which of the following gives a reason why the information given in the graph does not support this claim.
Put a tick ( ) in the box next to your answer.
The pattern shows an upward trend.
The pattern shows a downward trend.
There is no pattern.
(1)(Total 5 marks)
Q21.The diagram shows a transformer.
(a) (i) Is the transformer in the diagram being used as a step-up transformer or as a step-down transformer?
Put a tick ( ) in the box next to your answer.
a step-up transformer
a step-down transformer
Give a reason for your answer.
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(ii) Why is the core made of iron?
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(b) The power supply to a laptop computer contains a transformer designed to change the 230 V mains input to a 15 V output. The transformer has 920 turns on its primary coil.
Use the equation in the box to calculate the number of turns on the secondary coil.
Show clearly how you work out your answer.
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Number of turns on the secondary coil = .............................................(2)
(Total 4 marks)
Q22.(a) The diagram shows a simple transformer made by a student. The student has designed the transformer to light a 3.0 V lamp using a 1.0 V power supply.
(i) What name is given to the part of the transformer that is made of iron?
Draw a ring around your answer.
centre connector core(1)
(ii) When the power supply is switched on, the lamp is not very bright.
Suggest one change that the student can make to increase the brightness of the lamp.The 1.0 V power supply cannot be changed.
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(b) The diagram shows part of the National Grid system. The transformers, J, K, L and M, are an essential part of the system.
(i) Which transformer, J, K, L or M, is a step-up transformer?
Write your answer in the box.
(1)
(ii) Some scientists claim to have found evidence to suggest that children living near to overhead power lines are more likely to develop leukaemia. However, the scientists are not sure that the power lines are the cause of the problem.
The evidence from this and other investigations may worry some people.
What do you think scientists should do?
Put a tick ( ) in the box next to your answer.
Scientists should always publish the evidence from investigations immediately.
Scientists should ignore any evidence from investigations that may worry people.
Scientists should publish the evidence from an investigation only when theyhave found out as many facts as possible.
(1)(Total 4 marks)
Q23.The diagram shows the apparatus used by a student to investigate a transformer.
(a) The transformer made by the student would not have worked if the core had been made from aluminium and not iron.
Why?
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(b) The student made changes to the number of turns used to make the secondary coil.He then measured the potential difference across the secondary coil after each change.The graph shows the student’s results.
(i) What range of values was used for the number of turns on the secondary coil?
From .............................. to ..............................(1)
(ii) When he drew the line of best fit, the student ignored one of the data points.
Why?
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(iii) What is the minimum number of turns needed on the secondary coil for the transformer to act as a step-up transformer?
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Give a reason for your answer.
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(c) A radio can be used with a 9 V battery or it can be plugged into the 230 V mains electricity supply using an adapter. The mains adapter contains a transformer.
Why must the mains adapter contain a transformer?
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(Total 6 marks)
Q24.(a) In the National Grid, very large step-up transformers link power stations to the transmission
cables.
A transformer used for this purpose has 800 turns on its primary coil and 12 800 turns on its secondary coil. The p.d. (potential difference) across its primary coil is 25 kV.
Use the equation in the box to calculate the p.d. across its secondary coil.
Show clearly how you work out your answer.
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p.d. across secondary coil = .................................................. volts(2)
(b) The diagram shows the structure of a transformer.
(i) The primary and secondary coils of a transformer are made of insulated wire.
Why is this insulation necessary?
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(ii) Why is the core made of iron?
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(iii) Explain how the transformer works.
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(c) Before 1926, large towns had their own local power stations. After 1926, these power stations were connected to form the National Grid.
Give two advantages of having a National Grid system.
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(Total 9 marks)
Q25.Batteries inside laptop computers are charged using laptop chargers. The laptop charger contains a traditional transformer.
(a) The alternating current flowing through the primary coil of the transformer creates an alternating current in the secondary coil.
Explain how.
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(b) (i) Use information from the diagram to calculate the potential difference the charger supplies to the laptop.
Use the correct equation from the Physics Equations Sheet.
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Potential difference = .......................................................... V(2)
(ii) Calculate the current in the primary coil of the transformer when the laptop is being charged.
Assume the transformer is 100% efficient.
Use the correct equation from the Physics Equations Sheet.
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Current = .......................................................... A(2)
(c) Switch mode transformers can be used in mobile phone chargers.
Switch mode transformers and traditional transformers can both use the UK mains supply.
The switch mode transformer is smaller and lighter than the traditional transformer used in the laptop charger.
Give one other advantage of the switch mode transformer.
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(d) Laptop batteries and mobile phone batteries can only be recharged a limited number of times. After this, the batteries cannot store enough charge to be useful. Scientists are developing new batteries that can be recharged many more times than existing batteries.
Suggest one other advantage of developing these new batteries.
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(Total 9 marks)
Q26.(a) The diagram shows the structure of a traditional transformer.
Use words from the box to label the diagram.
aluminium brass iron large primary secondary
(3)
(b) Batteries inside laptop computers are charged using laptop chargers. The laptop charger contains a traditional transformer.
The laptop charger contains a step-down transformer.
What does a step-down transformer do?
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(c) The transformer used in a modern mobile phone charger is a switch mode transformer. This is different to the traditional transformer used in the laptop charger.
Give one advantage of using a switch mode transformer, rather than a traditional transformer.
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(d) Laptop batteries and mobile phone batteries can only be recharged a limited number of times. When a battery cannot be recharged, it is better to recycle the battery than to throw it away.
Draw a ring around the correct answer to complete the sentence.
(iii)
an environmental
The batteries are recycled mainly due to a political consideration.
a social
(1)(Total 6 marks)
Q27.The diagram shows a transformer with a 50 Hz (a.c.) supply connected to 10 turns of insulated wire wrapped around one side of the iron core.A voltmeter is connected to 5 turns wrapped around the other side of the iron core.
(a) What type of transformer is shown in the diagram?
Draw a ring around the correct answer.
step-down step-up switch mode
(1)
(b) The table shows values for the potential difference (p.d.) of the supply and the voltmeter reading.
p.d. of the supplyin volts
Voltmeter readingin volts
6.4 3.2
3.2
6.4
(i) Complete the table.(2)
(ii) Transformers are used as part of the National Grid.
How are the values of p.d. in the table different to the values produced by the National Grid?
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(c) Transformers will work with an alternating current (a.c.) supply but will not work with a direct current (d.c.) supply.
(i) Describe the difference between a.c. and d.c.
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(ii) Explain how a transformer works.
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(Total 10 marks)
Q28.The diagram shows an a.c. generator.
The coil rotates about the axis shown and cuts through the magnetic field produced by the magnets.
(a) (i) A potential difference is induced between X and Y.
Use the correct answer from the box to complete the sentence.
electric generator motor transformer
This effect is called the ..................................................... effect.(1)
(ii) What do the letters a.c. stand for?
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(iii) Name an instrument that could be used to measure the potential difference betweenX and Y.
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(b) Graph 1 shows the output from the a.c. generator.
Graph 1
(i) One of the axes on Graph 1 has been labelled ‘Potential difference’.
What should the other axis be labelled?
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(ii) The direction of the magnetic field is reversed.
On Graph 1, draw the output from the a.c. generator if everything else remains the same.
(2)
(iii) The output from the a.c generator is changed to be half-wave rectified.
Draw the half-wave rectified output on Graph 2.
Graph 2
(2)
(iv) State the name of a component that may be used for the half-wave rectification of a.c.
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(c) The number of turns of wire on the coil is increased. This increases the maximum induced potential difference.
State two other ways in which the maximum induced potential difference could be increased.
1 ......................................................................................................................
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2 ......................................................................................................................
.........................................................................................................................(2)
(Total 11 marks)
M1. (a) output voltage less than (the) input voltageor 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)
1
(b) any two from
(made of soft) iron
laminatedor designed to reduce eddy currentsor made of thin slices with slices of insulating material between them
core(s) joined to make a ring2
[3]
M2. 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 side1
of insulated wireor insulated coil
1
number of turns on primary coil/coil 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 coil
1
core of laminated ironor core of (soft) iron
1[4]
M3. (a) (i) Ironfor 1 mark
1
(ii) V/240 = 2000/10 000V = 48V
for 1 mark each3
(b) changing current in primary causes changing (magnetic) field in core links to secondary inducing voltage (emf) in secondary (NOT current) secondary voltage/current is alternating
for 1 mark each4
(c) magnetic field not changing/no electromagnetic induction because direct currentfor 1 mark each
2[10]
M4. (i) ironfor 1 mark
1
(ii) 20gains 2 marks
else workinggains 1 mark
2
(iii) reverse input/outputfor 1 mark
or increase secondary turns1
[4]
M5. (a) (i) one of the following:
• increase number of turns on the secondary coil
• decrease number of turns on the primary coil1
(ii) constructed in (thin) layers1
(b) (i) transformers only work with a c1
(ii) used to increase or decrease or change voltage or current
reducing the energy or heat or power loss (along the cables)1
or reduce to safe domestic levelmust be consistent with first answer
1
(iii) (several metres of) air gives good electrical insulation (between cables and earth) or reduce chance of earthing or sparks or arcing
or to avoid people touching it1
(c) (i)
accept
or 1
(ii) Np = 4000
for 1 mark2
(d) (i) resistance of cable decreases1
(ii) convection (to the air)orconduction (to the air)
not radiation1
[11]
M6. (i)
accept input for primaryaccept output for secondary
accept or correct transposition1
(ii) 60allow 1 mark for correct transformation
2[3]
M7. (a) 10 500allow 1 mark for 75 × 32 200 ÷ 230
2
(b) any three from:
• alternating current (a.c.) in the primary (coil)
• produces a changing magnetic field / flux (in the core)
• which is made of (laminated soft) iron
• this inducesmust be idea of inducing something in the secondary coil
• an alternating potential difference across the secondary coilaccept voltage for potential difference
3[5]
M8. (a) step-down (transformer)1
(b) alternating currentaccept minor misspellings butdo not credit ‘alternative current’
1
(c) (i)(ii) magnet
attracts
upwardscorrect order essentialaccept ‘up’
3[5]
M9. (a) (i) step-down (transformer) because fewer turns on the output/secondary (coil)no credit for just ‘step-down transformer’accept ‘…less turns…’do not credit ‘…fewer coils…’or ‘the p.d. across the input / primary will be greater than the p.d. across the output / secondary’
1
(ii) to prevent a short (circuit)(through the turns of wire or through the coredo not credit references to safety or heat (insulation)
1
(iii) (easily) magnetised (and demagnetised)accept ‘(it’s) magnetic’do not accept ‘because it’s a conductor’
1
(b) 2250correct substitution
eg gains 1 mark
or appropriate transformation
eg (p.d. across secondary =)
× p.d. across primary gains 1 mark
2
(c) any two from:
• to reduce the voltage / p.d. (of the domestic supply)or to reduce to 230 Vallow ‘to reduce to 240 V’do not credit ‘reduce current to 230V’
• higher voltage difficult to insulate
• higher voltage (would) result in (fatal) electric shocknot just ‘less dangerous’
• domestic appliances are not designed for (very) highvoltage (input) / (are designed) for 230V
do not credit ‘to increase efficiency’ / ‘to save energy’ do not credit just ‘it’s safer’
2
(d) any two (1) each
• if the (local) power station breaks down / fails / demand /load exceeds supply
1
or words to that effect
• electricity / power can be switched from elsewhere in thesystem / from other power station(s)
or words to that effect
• electricity can be generated in places remote from customersor words to that effect
• (in total) fewer power stations are needed
• power available in rural / remote areas
• National Grid allows for (better) control of supply and demanddo not credit just cheaper / more efficient / safer
1[9]
M10. (a) (i) secondary(coil) / output (coil)do not accept just coil
1
(ii) coredo not accept for either mark it is made out of iron ore
1
(laminated soft) ironallow 1 mark for ‘it is made out of iron core’
1
(iii) magnetic fieldaccept magnetism / magnetic force
1
(which is) changing / alternatingdirection (of field) changes / strength (of field) variesscoring second mark is dependent on first mark
1
(b) ...step-up .... step-down ...both in the correct order
1
(c) Do not build new houses ....1
Build new power lines away ....deduct 1 mark for any other(s) to a minimum total of (0)
1[8]
M11. (a) (i) (quickly) becomes magnetizedor (quickly) loses its magnetismor ‘it’s (a) magnetic (material)’any reference to conduction of electricity/heat nullifies the mark
1
(ii) any four from:
• insulation prevents electricity/current flowing through the iron/coreor ‘insulation so electricity/current only flows in the wires/turns/coils’
• alternating current/a.c. in the primary (coil)
• produces a changing magnetic field (in the iron/core)
• (and hence magnetic) field in the secondary (coil)
• induces/generates/produces an alternating potential difference/p.d./voltage across the secondary (coil)
• (and hence) alternating current/a.c. in the secondary (coil)4
(b) 80 (turns)or credit (1) for any equation which if correctly evaluated would give 80 exampleexample
2[7]
M12.(a) (i) primary
on left hand side1
secondaryon right hand side
1
(ii) step-up1
(b) Marks awarded for this answer will be determined by the quality of communicationas well as the standard of the scientific response.
0 marks
No relevant content
Level 1 (1–2 marks)There is a basic explanation of how an a.c. output is produced.
Level 2 (3–4 marks)There is a clear explanation of how the transformer acts as a step-up.
Level 3 (5–6 marks)There is a clear and detailed explanation of how the transformer acts as a step-up.
examples of the physics points made in the responseextra information
• the magnetic field (in the iron core) is changing / alternating / varyingaccept magnetic flux
• the magnetic field links with the secondary / other coil
• a potential difference is induced in the other coil
• the potential difference induced in the other coil is alternating / changing
• the number of turns on the output is greater than the number on the input
• the turns ratio determines the particular value of the output voltage / potential difference
6
(c) operates at (much) higher frequencyaccept a specific frequency value between 50 kHz and 200 kHzaccept operates at higher efficiency
1[10]
M13. (a) an alternating input / current to primary (coil)1
which produces an alternating magnetic fieldaccept changing magnetic field for alternating magnetic fieldif first mark point scores then ‘alternating’ not required here
1
in the (iron) core
this magnetic field links with the secondary coil1
which induces an (alternating) voltage / p.d. across thesecondary (coil)
1
(b) 0.21accept 0.2 or any answer that rounds to 0.21allow 1 mark for correct equationie power input = power outputorallow 1 mark for substitution into correct equationie 230 × Ip = 12 × 4
2[7]
M14. (a) (i) must use an a.c.1
(ii) more than 301
(b) ironreason can only score if iron is chosen
1
because it can be magnetised (and demagnetised) easily1
[4]
M15. (a) (it is) magneticor will carry (an alternating) magnetic fieldor magnetises and demagnetises (easily)reference to conduction negates the mark
1
(b) so the current / electricity does not flow through the iron / coreaccept ‘so the current / electricity / wires do not short (circuit)’responses in terms of heat insulation negate the markignore references to safety
1
(c) 5.75 or 5.8 or 6(.0)allow for 1 mark either
orp.d. = 230 ÷ 40
2
V / volt(s)1
[5]
M16. (a) (i) iron1
(ii) step-down (transformer)1
(b) any one from:
• after the power station
• after the generator
• before the power lines
• before the pylons1
(c) each correct (1)in its correct place
current
coil
field
core
ends5
[8]
M17. (a) (i) (laminated soft) irondo not accept steel
1
(ii) produces a magnetic fieldaccept magnetic flux
which is alternating / changing / varying
and which induces / produces an alternating / changing potentialdifference across the secondary coil
accept current / voltage3
(b) 3067 (V)allow all 3 marks for 3060 to 3070 (V)
gains 2 marks
gains 1 mark3
[7]
M18. (a) 400 000allow 1 mark for correct substitution ie
or
2
volt(s) / Van answer 400 gains 2 marksan answer 400 kilovolts / kV gains 3 marksalthough the unit mark is independent to gain 3 marks it must be consistent with the numerical value
1
(b) any one from:
do not accept any response in terms of heat insulation, safety or electric shock
• (so that there is) no short circuit
• (so that the) current goes round the coildo not accept electricity for current
• (so that the) current does not enter the core1
(c) (the alternating p.d. in the primary causes) an (alternating)current in the primary
reference to the current in the core negates this mark1
(causes an) alternating / changing (magnetic) field in the (iron) core1
induces (alternating) p.d. across the secondary (coil)accept in / through or similar for acrossaccept current for p.d.accept output (coil) for secondary (coil)to gain 3 marks the sequence must be correct
1[7]
M19. (a) 10
allow 1 mark for correct substitution ie 2
(b) any one from:
• to prevent short circuiting
• to ensure that the current flows / goes round the coil
• to prevent the current entering the coredo not accept electrocutiondo not accept electricity for currentanswers including heat / energy loss negate mark
1
(c) (i) (soft) irondo not accept ‘steel’
1
(ii) can be magnetised
because it is magneticanswers including it’s a conductor negate mark
1[5]
M20. (a) ironaccept any unambiguous correct indication
1
(b) (i) step-down (transformer)do not accept down step or a description
1
(ii) less thanaccept any unambiguous correct indication
1
(c) (i) 20001
(ii) There is no pattern.1
[5]
M21. (a) (i) step-upboth parts required
more turns on the secondary / output (coil)do not accept coils for turns’secondary output is greater than primary input’ is insufficient
1
(ii) (easily) magnetised (and demagnetised)accept (it’s) magneticit’s a conductor negates answer
1
(b) 60
allow 1 mark for correct substitution, ie 2
[4]
M22. (a) (i) core1
(ii) increase number of turns on secondary (coil)do not accept coils for turns
orreduce number of turns on primary (coil)
1
(b) (i) J1
(ii) Scientists should publish the evidence from an investigation onlywhen they have found out as many facts as possible
1[4]
M23. (a) aluminium cannot be magnetisedaccept aluminium is not magnetic“it” refers to aluminiumdo not accept aluminium is not easily magnetisedreference to conduction and aluminium negates markiron can be magnetised is insufficient
1
(b) (i) 10 to 50either order
1
(ii) (data is) anomalousaccept does not fit the patternit is an error is insufficient
1
(iii) 21accept 22do not accept any fraction of a turn ie 20.1
1
secondary p.d. (just) larger than primary p.d.accept output (just) larger than input/2V
orthere must be more turns on the secondary coil than primary coil
do not accept coil for turns1
(c) to reduce/step-down the (input) p.d./voltagemains p.d. is too high is insufficientstep-down transformer is insufficientanswers in terms of changing/ stepping-up current or fuse blowingor not working with 230 volts are insufficientany mention of step-up negates markstepping down both voltage/p.d. and current negates mark
1[6]
M24.(a) 400 000allow 1 mark for correct substitution ie
or
2
(b) (i) any one from:do not accept any response in terms of heat insulation, safety or electric shock
• (so that there is) no short circuit
• (so that the) current goes around the coildo not accept electricity for current
• (so that the) current does not enter the core1
(ii) (easily) magnetised (and demagnetised)accept ‘(it’s) magnetic’ do not accept ‘because it’s a conductor’
1
(iii) alternating current in the primary (coil)1
produces a changing magnetic field (in the core)1
this induces an (alternating) potential difference across the secondary (coil)1
(c) any two from:
• if the (local) power station breaks down / fails / demand / load exceeds supply
• electricity / power can be switched from elsewhere in the system / from other power station(s)
• electricity can be generated in places remote from customers
• (in total) fewer power stations are needed
• power available in rural / remote areas
• National Grid allows for (better) control of supply and demand2
[9]
M25.(a) (the alternating current creates) a changing / alternating magnetic field1
(magnetic field) in the (iron) coreaccept that links with the secondary coilcurrent in the core negates this mark
1
(causing a) potential difference (to be) induced in / across secondary coilaccept voltage for p.d.
1
(b) (i) 20
allow 1 mark for correct substitution, ie
or 2
(ii) 0.3
or
correct calculation using 230 × Ip = their (b)(i) × 3.45allow 1 mark for correct substitution, ie230 × Ip = 20 × 3.45allow ecf from (b)(i) for 20OR
substitution into this equation 2
(c) (switch mode transformers) use (very) little power / current / energy when switched on but no load is applied
accept no for littleignore it is more portabledo not accept electricity for power / current / energy
orit is more efficient
accept does not get as hot or less heat produced1
(d) any one from:
• fewer (waste) batteries have to be sent to / buried in land-fill
• the soil is polluted less by batteries in land-fill
• fewer (waste) batteries have to be recycled
• fewer batteries have to be made
• less raw materials are used in making batteries
• customers have to replace their batteries less oftenlonger lifetime is insufficient
• customers have to buy fewer (replacement) batteriesit costs less is insufficient
1[9]
M26.(a) ironcorrect positions only
1
primary1
secondary1
(b) (it) decreases the p.d.accept it would increase currentaccept voltage for p.d.the voltage goes from 230(V) to 20(V) is insufficientdo not accept decreases current / energy / powerdo not accept decreases p.d. / voltage and current
1
(c) any one from:
• lighteraccept it is easier to carry around
• smaller
• use (very) little power / current / energy when switched on and no load / phone not connected
accept no power / current / energy is drawndo not accept electricity for power / current / energy
• more efficientaccept does not get as hot or less heat produced
1
(d) an environmental1
[6]
M27.(a) step-down1
(b) (i) 1.6correct order only
1
12.81
(ii) values of p.d. are smaller than 230 V1
(c) (i) a.c. is constantly changing directionaccept a.c. flows in two / both directionsaccept a.c. changes direction(s)a.c. travels in different directions is insufficient
1
d.c. flows in one direction only1
(ii) an alternating current / p.d. in the primary creates a changing / alternating magnetic field
1
(magnetic field) in the (iron) corecurrent in the core negates this markaccept voltage for p.d.
1
(and so) an alternating p.d.1
(p.d.) is induced across secondary coil1
[10]
M28.(a) (i) generator1
(ii) alternating current1
(iii) voltmeter / CRO / oscilloscope / cathode ray oscilloscope1
(b) (i) time1
(ii) peaks and troughs in opposite directions1
amplitude remains constantdependent on first marking point
1
(iii) wave modified to omit all values above or below x-axis1
same amplitude and wavelength as originaldependent on first marking point
1
(iv) diode1
(c) any two from:
• increase speed of coil• strengthen magnetic field• increase area of coil
do not accept larger2
[11]
E1. Most candidates gained the mark in (a) and gave at least one correct feature in (b). Some students thought that soft iron is soft, as they had written ‘made of iron’ as their first feature and ‘soft’ as their second feature.
E2. Many candidates appeared to think that a current is meant to flow from the input coil to the output coil through the core of a transformer. They either stated this was the case or omitted to mention that the coils are of insulated wire. Many answers muddled coils and turns and only a minority was sure that for a step-down transformer the greater number of turns would be on the input coil.
E3. Part (a) was well answered, very few missed iron as the transformer core material and the great majority calculated the output voltage correctly. In part (b) a few totally correct answers were obtained but many candidates gave inadequate information. The fact that the magnetic field had to be changing to induce a voltage was not appreciated in this context by many candidates, even those who were to go on and answer part (c) correctly. For those candidates who did start their answers with an a.c. in the primary coil many scored near full marks, the only common error being to induce a current rather than a voltage in the secondary coil. In part (c) many candidates attributed the zero output voltage to the battery supplying d.c. rather than a.c. but fewer went on to explain that without a changing magnetic field a voltage would not be induced.
E4. The answers to this question were generally pleasing. In (iii) the expected scoring response was to reverse the input and output terminals but full credit was also given to the many candidates who correctly rewired the transformer.
E5. Candidates found part (a) difficult. Many answers simply described changing number of turns without specifying the coil or if it would cause an increase or decrease. The vast majority of candidates seemed to think that a laminated iron core was covered in plastic. Part (b) was not well understood, with few sensible responses given to part (iii). In part (c) many candidates were able to produce the correct equation and continue to complete a correct calculation. In part (d) the better candidates were able to relate their answer to resistance.
E6. This question was often high scoring.
Most candidates could recall the equation needed in this part and many candidates went on to calculate the correct answer.
E7. (a) Most candidates were able to rearrange the numbers to 75 × 32 200 ÷ 230 and so correctly gave 10 500 as the number of turns, a minority of candidates incorrectly added a unit.
(b) There were many incorrect answers. Some candidates seemed to have invented their own
set of questions; ‘Is this a step-up or a step-down transformer? How do you know and what else might it be used for?’ Others wrote about current or, voltage, flowing through the core to the secondary coil. A significant minority of candidates misunderstood the term ‘turns’ and seemed to think that the coils rotate.
E8. (a) A third of candidates gained the mark by recognising the correct transformer.
(b) A third of candidates knew that a.c. stands for alternating current.
(c) (i) Most candidates recognised that when a current flows in a coil, the coil becomes a magnet.
(ii) Two thirds of candidates gained both marks by recognising that the coil attracts the iron bolt which moves upwards.
E9. (a) (i) There was no mark just for ticking the second box. Candidates had to explain how they knew that the transformer in the diagram is being used as a step-down transformer. Many failed to do this because they wrote that there are more coils on the output side than there are on the input side. Candidates are expected to distinguish between the terms ‘coils’ and ‘turns’ with reference to a transformer. Some correctly stated that there are fewer turns on the output coil.
(ii) About a quarter of candidates correctly explained that, otherwise, the current would be conducted through the core or would short across the coil. Those who suggested that the insulation would reduce or prevent heat transfer or protect against electric shock did not gain the mark.
(iii) Most candidates incorrectly thought this was because iron is an electrical conductor. Others had the correct idea when they stated that iron is a magnetic material and they gained a mark for this. Others went further and stated that iron is a soft magnetic material and so it is easily magnetised and easily demagnetised.
(b) About half the candidates were able to use the equation correctly to calculate the potential difference across the secondary coil.
(c) Many candidates knew this was to reduce the potential difference. Few candidates knew that it increases the current. The difficulty in insulating high voltage was hardly ever referred to. Vague statements such as, ’It’s safer’, did not gain the second mark.
(d) The most popular form of an answer which gained two marks was to state that if the local power station breaks down then the National Grid will enable other power stations to be used. Very few answers were in terms of supply and demand.
E10. Foundation Tier
(a) (i) A majority of candidates identified the secondary coil.
(ii) Only a small minority of candidates could identify the transformer’s core and state that it is made of iron.
(iii) A small minority of candidates gained any credit for magnetic field, and only the better candidates knew it is alternating. Most candidates claimed that the current passes through the core to the secondary coil.
(b) The majority of candidates correctly identified the ‘step-up’ and ‘step-down’ transformers.
(c) The majority of candidates gained both marks by realising that to reduce the risk, new houses should not be built near to existing power lines and that new power lines should not be built near to where people live.
Higher Tier
(a) (i) Nearly all candidates could name the secondary coil.
(ii) The majority of candidates could name the core and knew that it is made of iron.
(iii) The majority of candidates knew that there is a magnetic field in the core, but only about half of these candidates knew that it has to be a changing magnetic field.
Examiners were disappointed to note that a significant proportion of candidates continue to suggest that the core conducts an electric current from one coil to the other.
(b) Nearly all candidates correctly identified the ‘step-up’ and ‘step-down’ transformers.
The majority of candidates were able to identify two appropriate suggestions for reducing possible health risks from power lines.
E11. (a) (i)(ii) It was a common erroneous statement that the core of a transformer conducts electricity.Many candidates, in their responses to (a)(ii), failed to include any reference to the changing or alternating nature of the input, of the magnetic field or of the output.Few candidates explained why the coils are made of insulated wire.
(b) Most candidates gained both marks.
E15. (a) Just over half of the candidates gave a correct answer. Many candidates still seem to think that iron is used because it is a good electrical conductor.
(b) A large number of candidates thought the wire was insulated to stop energy losses or for safety purposes. Incorrect answers also showed many candidates think that potential difference flows. Only just over a third of candidates were able to give an acceptable answer.
(c) Nearly half of the candidates scored full marks. Those candidates who struggled either did not know which coil was the primary and which was the secondary, or were unable to rearrange the equation.A significant number of candidates did not know that the unit for p.d. is the volt.
E16. (a) (i) Most candidates knew that iron forms the core of a transformer.
(ii) Nearly two thirds of candidates correctly identified the step-down transformer but a number who gave the wrong answer had changed it from the correct one . possibly after reading the next part of the question which was about a step-up transformer.
(b) Under a third of candidates knew where the step-up transformer fits into the National Grid. This part question was not attempted by a tenth of the candidates.
(c) Most candidates (three quarters) scored four or five marks for this part question. The majority of lost marks were for the last answer where the most common error was to insert the word ‘coil’ or ‘wire’.
E17. (a) (i) Most candidates knew that the core of a transformer is made of iron.
(ii) This is a standard transformer question but only a minority of candidates could link a changing magnetic field to subsequent induction in the secondary coil.Nearly half of the candidates scored zero.References to the core conducting electricity were not uncommon.
(b) Over half of the candidates gave a numerically correct answer. The most common error was a failure to rearrange the equation correctly. (The resulting calculation was almost always correct!).
E18. (a) Almost three fifths of candidates correctly calculated the p.d. across the secondary coil. This was pleasing as candidates were required to rearrange the equation. Where there were calculation errors, some appeared to stem from efforts to resolve the calculation without the aid of a calculator. There are still issues about the relative sizes of letters to enable award of the unit mark, kV.
(b) Again, considering the frequency of this question it is surprising that only two fifths of candidates answered correctly. Many answers referred to electricity instead of current and there were frequent incorrect references to, not only electricity but also, potential difference flowing in the core. Other incorrect responses referred to either‘heat’/‘energy loss’ or related to safety issues such as risk of electrocution/shock.
(c) Very few candidates gained all 3 marks. This was probably the question which was least well answered out of the whole paper with just under half of candidates scoring zero. Very few candidates sequenced their answers. Mentioning that the p.d. across the primary causes a current to flow in the primary was rarely seen. However, better candidates that omitted this did say that the p.d. created an alternating magnetic field in the core which then causes an induced p.d./current in the secondary coil. Some candidates still believe that current flows directly through the core of the transformer from one coil to the other.
E19. (a) This calculation was completed correctly by three quarters of candidates. Those who did not have the correct calculation frequently did not show a full substitution into the equation and so lost the compensatory mark.
(b) Considering how many times this question has been asked, the answers given were poor. Most responses were in terms of electrocution and energy loss.
(c) (i) Most candidates scored this mark although ‘copper’ was a fairly common incorrect response.
(ii) Fewer candidates knew why iron is used, with many responses given in terms of electrical conduction.
