P1 Revision Booklet

Electromagnetic Induction

Medium (Grade C)

Q1.          (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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(1)

(c)     (i)      What material is the core of a transformer made from?
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(1)

(ii)     Why is the core made from this material?
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(1)
(Total 5 marks)

 

Q2.          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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(1)

(b)     The coils of the transformers are made of insulated copper wire.
Why is the wire insulated?
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(1)

(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)

 

Q3.          The diagram shows apparatus used to demonstrate the motor effect. X is a short length of bare copper wire resting on two other wires.

(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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(3)

(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.

          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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(3)

(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)

 

Q4.          The diagram below shows a transformer.

(i)      Name the material used to make the core of the transformer.
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(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.
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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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(1)
(Total 4 marks)

 

Q5.          (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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(1)

(ii)     Explain how a transformer works.
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(4)

(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)

 

Q6.          Many electrical appliances use the circular motion produced by their electric motor.
(a)     Put ticks () in the boxes next to all the appliances in the list which have an electric motor.
 
electric drill		
electric fan		
electric food mixer		
electric iron		
electric kettle		
electric screwdriver		

(2)

(b)     One simple design of an electric motor is shown in the diagram. It has a coil which spins between the ends of a magnet.

(i)      Give two ways of reversing the direction of the forces on the coil in the electric motor.
1 ........................................................................................................................
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2 ........................................................................................................................
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(2)

(ii)     Give two ways of increasing the forces on the coil in the electric motor.
1 ........................................................................................................................
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2 ........................................................................................................................
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(2)
(Total 6 marks)
 
Electromagnetic Induction-Mark scheme
M1.          (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 core
do not accept electrocution
do not accept electricity for current
answers including heat / energy loss negate mark
1

(c)     (i)      (soft) iron
do not accept ‘steel’
1

(ii)     can be magnetised
because it is magnetic
answers including it’s a conductor negate mark
1
[5]

M2.          (a)     (it is) magnetic
or will carry (an alternating) magnetic field
or magnetises and demagnetises (easily)
reference to conduction negates the mark
1

(b)     so the current / electricity does not flow through the iron / core
accept ‘so the current / electricity / wires do not short (circuit)’
responses in terms of heat insulation negate the mark
ignore references to safety
1

(c)     5.75 or 5.8 or 6(.0)
allow for 1 mark either

or
p.d. = 230 ÷ 40
2

V / volt(s)
1
[5]

M3.          (a)     (i)      it moves or experiences a force horizontally to the right 
for 1 mark
1

(ii)     A – moves in opposite direction or force reversed e.c.f. 
B – faster movement or larger force
(not move further)
for 1 mark each
2

(b)     turns clockwise
oscillates/reverses
comes to rest facing field/at 90o to field/vertically
for 1 mark each
3

(c)     number of turns or linear number density of turns current core
for 1 mark each
3
[9]

 

M4.          (i)      iron
for 1 mark
1

(ii)      20
gains 2 marks
          else working
gains 1 mark
2

(iii)     reverse input/output
for 1 mark
          or increase secondary turns
1
[4]

 

M5.          (a)     (i)      (quickly) becomes magnetized
or (quickly) loses its magnetism
or ‘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/core
or ‘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 example
example

2
[7]

 

M6.          (a)     electric drill, electric fan, electric food mixer and electric screwdriver
all four ticked and no others (2)
either all four of these ticked and only one other (1)
or any three of these ticked and none/one/two of the others (1)
2

(b)     (i)      reverse (the direction of the) current (1)
or reverse the connections (to the battery)
         reverse (the direction of the) magnetic field (1)
or reverse the (magnetic) poles /ends
do not credit ‘swap the magnets (around)’
2

(ii)     any two from:
•        increase the strength of the magnet(s)/(magnetic) field
do not credit ‘use a bigger magnet’
•        increase the current
allow ‘increase the voltage/p.d.’
allow add cells/batteries
allow increase the (electrical) energy
allow increase the power supply
allow ‘decrease the resistance’
allow ‘increase charge’
allow ‘ increase the electricity’
do not credit ‘use a bigger battery’
•        reduce the gap (between coil/armature
and poles/magnets)
allow increase the (number of) coils
•        increase the turns (on the coil/armature)
do not credit ‘use a bigger coil’
2
[6]