SPM 2003

ELECTROMAGNETISM PAPER 11The diagram shows an arrangement of apparatus to study the pattern of magnetic fields which are formed when current flows through conductors.SPM 2004

Which magnetic pattern is formed on the cardboard when both switches are closed ?

2.The diagram shows an electromagnet.

SPM 2005

Which factor does not influence the strength of the electromagnet ?AMaterial used for the wire

BMaterial used for insulator of the wire

CNumber of turns of wire

DCurrent flowing in the wire..3.When the switch is closed in the circuit below , wire R deflects. SPM 2004

The direction of the deflection can be determined by

AFleming s right hand rule

BFlemings left hand rule

CMaxwell s corkscrew rule

4.The diagram shows a coil of wire placed next to a magnet. The galvanometer pointer deflects when the magnet is pushed into the coil.

SPM 2004

Which action will increase the deflection of the galvanometer pointer ?

AThe magnetic pole is reversed

BThe number of coils is increased

CThe coil is made from insulated wire

DThe magnet is pushed slowly into the coil.

5. The diagram shows a magnet oscillating in a solenoid. Which of these will not increase the deflection of the galvanometer pointer ?AReversing the polarity of the magnet

BIncreasing the number of coils in the solenoid

CDecreasing the diameter of the solenoid

DIncreasing the oscillation speed of the magnet.6Which diagram shows the correct direction of the induced current when the magnet is moved in the direction shown ?

SPM 2005

7The diagram shows the structure of an ideal transformerSPM 2005

What is the potential difference across the bulb ?

A7 V

B24 V

C30 V

D60 V

E160 V

8 The diagram shows a circuit containing an ideal transformer.

Which statement is correct about the brightness of bulb P and bulb Q ?

A Bulb P is brighter than bulb Q

B Bulb P and bulb Q have the same brightness

C Bulb Q is brighter than bulb P9. The diagram shows the structural design of an electric motor.

10. The diagram shows an electric generator connected to a cathode ray oscilloscope.

Which trace represents the e.m.f induced in the generator when the coil is rotated at a constant speed.?

SPM 200711. Diagram 23 shows a solenoid.

Which of the following rules may be used to determine the direction of the current in the coil ?

AFleming s Left Hand Rule

BFleming s Right Hand Rule

CRight Hand Screw Rule

DRight Hand Grip Rule.

12. Diagram 24 shows a conductor wire placed in a magnetic field.

When the switch is on , the wire initially moves towards

AW

BX

CY

DZ

13Diagram 25 shows a transformer connected to a cathode ray oscilloscope ( CRO)

Which of the following wave traces is correct when the extra coil is on the core and connected in series with the secondary coil ?

14The purpose of using laminated iron core in a transformer is to

Areduce resistance

Breduce eddy current

Cprevent flux leakage

Dmagnetized and demagnetized iron core easily.

15Diagram 26 shows a model of the transmission of electrical energy and includes three identical bulbs , P ,Q and R.

Which comparison of the brightness of the bubs is correct ?

P

Q

R

ABrightest

Brighter

Bright

BBright

Brighter

Brightest

CBrighter

Brightest

Bright

DBrightest

Bright

Brighter

PAPER 2 (SECTION A)SPM 2007Diagram 7 shows a simple transformer

(a) (i) Name the type of the transformer .

..

[1 mark]

(ii)State why soft iron is used as the transformer core.

.

[1 mark]

(b) The number of turns on the primary coil in Diagram 7 is 1 000.

Calculate the number of turns on the secondary coil.

[2 marks]

(c) The transformer in Diagram 7 is used to switch on an electrical appliance. The

current in the primary coil is 0.1 A and the efficiency is 75 %.

(i) Calculate the output power of the transformer.

[2 marks]

(ii) An electrical appliance which needs 20 W of power is connected to the

transformer output.

Suggest a modification to the transformer that enables the appliance to

function correctly.

[1 mark]

(d) A student connects a television which uses direct current to the output of the

transformer in Diagram 7.

When the television is switched on , it does not function.

(i ) Why the television does not function ?

[1 mark]

(ii) An electrical component is connected to the output of the transformer so that the television functions.

Name the electrical component and state how the connection is made.

[2 marks]

PAPER 2 (SECTION B)SPM 2005

Most of our electrical energy comes from hydroelectric power stations and thermal power stations. These power stations are connected by cables to transmit electricity to users in industries , offices , schools and houses. This system is called the national grid network.

(i)State the transformations of energy in a hydroelectric power station.

[ 1 mark]

(ii)Explain briefly the importance of the national grid network system in distributing electrical energy to the users.

[ 4 marks]

Figure 12.1 shows how a model of an electric transmission system can be set up in

laboratory. The model consists of a power station that generates 12 V of alternating

current ( a.c) that transmits the electrical energy to the users using transmission

wires and transformers P ,Q and R.

You are required to set up a model as in Figure 12.1 using the information in Table 12.1

Type of transformer core

Solid cuprum core

Laminated cuprum core

Solid soft iron core

Laminated soft iron core

(b) Using the information in Figure 12.1 and Table 12.1 determine :

(i)the numbers of turns in the primary and the secondary coil of transformers P, Q and R and show your working,

(ii)the type of core you will use in all the transformers and justify your choice,

(iiithe material you will use for the transmission wire and justify your choice.

[10 marks]

(c)If the resistance of the transmission wires between transformers P and Q in the model at is 30 , calculate :

(i) the current that flows in the transmission wire,

(ii) the power loss due to the heating effect of the current in the transmission wire.

[ 5 marks]

SPM 2006

Diagram 10.1 and Diagram 10.2 show wire coils connected to the ammeters

switches and d. c power supply.

When the switch is on and iron filings of the same amount is spread on each of the cardboard surface, the pattern of the iron filings is formed as shown in the diagrams.

(a)What is meant by magnetic field ?

[1 mark]

(b)Using Diagram 10.1 and Diagram 10.2 , compare the number of turns of the coils, the pattern of the iron filings and angle of deflection of the ammeter indicator.

[ 3 marks]

(c) State the relationship between the strength of the magnetic field and

(i) the pattern of the iron filings

(ii) the number of turn of the coils

[2 marks]

(d) Diagram 10.3 shows two thin copper strips , PQ and RS , connected to a circuit.

Explain what happens to PQ and RS , when the switch is on.

[ 4 marks]

(e) Diagram 10.4 shows an electric motor which is supplied with a 12 V a.c

(i) Explain how the motor is able to rotate

(ii) Using a 12 V a.c power supply , explain the modification that needs to be done on the motor and the external circuit to enable the motor to be a d.c electric motor and rotate faster.

[10 marks]

SPM 2004

Figure 4.1 shows circuits J,K , L, M and N each containing an ideal transformer.

Diodes in the circuits are used for the purpose of rectification.

(i) What is meant by rectification ?

(ii) Explain the working principle of a transformer.

(iii) You are asked to make a 12 V battery charger. Study the circuits , J ,K,L , M and N in Figure 4.1 and consider the following aspects :

type of transformer

ratio of number or turns in primary coil to secondary coil

type of rectification

characteristic of output current.

Explain the suitability of the above aspects and hence determine the most suitable circuit to make the battery charger.

Justify your choice.

[10 marks]

(b) Figure 4.2 shows a circuit consisting of a transformer , an ammeter and two light bulbs. The ammeter reading is 0.5 A and both light bulbs light up with normal brightness.

(i) What is the output of the transformer ?

(ii) Calculate the efficiency of the transformer ?[5 marks].

Materials of transmission wireConstantan

Copper

Aluminium

Nichrome

Number of turns of the coil

1200

1000

500

400

160

120

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