IT Phy F5 Topical Test 3 (BI)

PAPER 1

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TOPICAL TEST 3: ELECTROMAGNETISM

1 Diagram 1 shows a current flowing

in a straight wire passes through a horizontal cardboard. Two compasses are placed at positions x and y.

Diagram 1

Which of the following pairs of arrow shows the direction of the pointer of the compasses correctly?

At x At y

A

B

C

D

Questions 2 and 3 are based on Diagram 2.Diagram 2 shows a current-carrying solenoid.

Diagram 2 2 What is the rule that used to

determine the direction of the magnetic field produced by a current flowing through a solenoid?A Right-hand grip ruleB Maxwell’s screw ruleC Fleming’s left-hand ruleD Fleming right-hand rule

3 Which of the following is true about the poles and direction of current flowing at each end?

PolesDirection of current flowing at the end of

coil

P Q End P End Q

A North South Clockwise Anti-clockwise

B South North Clockwise Anti-clockwise

C North South Anti-clockwise

Clockwise

D South North Anti-clockwise

Clockwise

4 Which of the following does not affects the strength of the magnetic field produced by an electromagnet?A The current in the solenoid.B The shape of coil that is used.C The number of turns on

the solenoid.D The type of current flows in

the solenoid.

5 Diagram 3 shows two straight wire x and y pass through a cardboard. Some iron fillings is sprinkled on the cardboard.

Diagram 3Which of the following shows the magnetic field correctly?

A

B

C

D

6 Which of the following diagrams shows the correct catapult field?A C

B D

7 Diagram 4 shows a straight wire placed vertically in an uniform magnetic field.

Diagram 4

In which direction will the catapult force act?A East C WestB South D North

8 Diagram 5 shows a simple motor.

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Diagram 5

What will happen to the coil when the switch is closed?A The coil does not rotate at all.B The coil rotates in clockwise

direction.C The coil rotates in anticlockwise

direction.D The coil stationary in a vertical

position.9 Diagram 6 shows an electric circuit

consists of two rectangular aluminium foils which are placed close to each other and connected to a dry cell.

Diagram 6 Which of the following shows the acting force correctly when the switch is closed?A C

B D

10 Diagram 7 shows a conducting rod placed in a magnetic field.

Diagram 7

In which direction will the conducting rod moves when the switch is closed?

Questions 11 and 12 are based on Diagram 8.Diagram 8 shows output terminals of an electric generator is connected to a cathode-ray oscilloscope(C.R.O.).

Diagram 8

11 Which of the traces will be displayed on the screen when the time-base is turned on?A

B

C

D

12 Which of the following cannot increase the magnitude of the current produced by the electric generator shown?A Using a stronger magnetB Rotating the coil at a higher speedC Increasing the number of turns on

the coilD Winding the coil on a stainless

steel core

Questions 13 and 14 are based on Diagram 9.Diagram 9 shows an experimental set-up where a bar magnet placed near a solenoid which is connected to a sensitive galvanometer.

Diagram 9

13 Which of the following actions will not produce an induced current flow through the sensitive galvanometer?A Moving the magnet towards the

solenoid.B Moving the solenoid towards the

magnet.C Both the magnet and solenoid are

moving towards each other.D Both the magnet and solenoid are

moving with the same velocity.

14 One of the poles of solenoid can be determined by using a law. What is the law should be used?A Lenz’s lawB Faraday’s lawC Maxwell’s screw ruleD Fleming’s right-hand rule

15 Diagram 10 shows a current-time graph from a power supply.

Diagram 10

Based on the graph, calculate the root mean square (r.m.s.) current for the power supply.A 2.0 A C 5.66 A


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B 2.83 A D 8.0 A

16 Why is the soft iron core is used in a transformer?

A To reduce resistance produced.B To produce a uniform magnetic

field.C To increase the generation of

electrical energy.D To be magnetised and

demagnetised easily.

17 Diagram 11 shows a graph of input voltage, Vi against the time, t for a transformer.

Diagram 11

If the transformer has half of the turns in its secondary coil than its primary coil, which of the following graph shows the output voltage, Vo

correctly?A

B

C

D

18 A transformer is used to change the main voltage of 240 V to provide a 6 V supply for a bulb. If the number of turns in primary coil is 1 000, calculate the number of turns required in the secondary coil.A 25 C 80B 40 D 167

19 What is the function of the laminated iron core in a transformer?

A To reduce resistance of coilB To reduce eddy currentC To reduce leakage of magnetic

fluxD To reduce the strength of the

magnetic field produced

20 A step-up transformer is used to increase the input voltage from 240 V to 360 V. If the efficiency of the transformer is 75% and the current flowing through the primary coil is 1.5 A, what is the current flowing through the secondary coil?A 0.75 A C 1.5 AB 1.125 A D 2.25 A

21 A transformer has 1 000 turns and 50 turns in its primary and secondary coil respectively. Assume the transformer has 100%

efficiency, what is the output power of a 5 resistor connectedto the secondary coil, if the primary coil is connected to a 240 V power supply?

A 1.2 W C 12 WB 2.4 W D 28.8 W

22 What is the advantage of using an alternating current supply? A Generation cost is lower.B The power supply can be changed

easily.C The voltage of the current can be

changed easily.D The frequency of the current can

be easily maintained at a constant value.

23 Why the electrical energy is normally transmitted at high voltage?A To minimise the energy loss.B To transmit as large as possible of

current.C Transmitting cables normally

have very low resistance.D Transmitting system do not

require a step-up transformer.

24 Electrical energy is transmitted at a rate of 250 MW. The current in the transmitting cable is 820 A. If the cable has a resistance of 45 , calculate the power loss in the transmission process.A 14 MW C 30 MWB 21 MW D 56 MW

25 A power station generates 50 MW of power at a voltage of 400 kV. If the resistance of the cable is 25 per km, calculate the power loss due to the 500 km length of transmission cable.A 390 kW C 8 MWB 1.5 MW D 5 MW

1 Diagram 1.1 shows a sections of a moving coil

galvanometer. N and S represent the North pole and the South pole of a permanent magnet respectively.


PAPER 2 SECTION A

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Diagram 1.1

(a) Diagram 1.2 shows the plan of the galvanometer. On Diagram 1.2, draw the pattern of the magnetic field which exists between N and S.

Diagram 1.2 [2 marks](b) A current flows through the galvanometer so that the

pointer deflects and shows a fixed reading of current. (i) What type of current that flows through the

galvanometer?

_____________________________________[1 mark]

(ii) Explain how the coil of the galvanometer can

rotate? ________________________________________________________________________________________________________________________

[3 marks]

(iii)What causes the rotation of the coil to stop?

________________________________________ [1 mark]

2 Diagram 2.1 shows four compasses placed on a horizontal

cardboard. A straight wire which is perpendicular to the cardboard passes through the centre of the cardboard. When there is no current flows through the wire, the pointers of the compasses point towards North as shown in Diagram 2.1.

Diagram 2.1

(a) In the Diagram 2.2, draw arrows to represent the directions of pointers when current flows vertically upwards through the wire.

Diagram 2.2 [2 marks](b) Diagram 2.3 shows current flows through a solenoid,

RS. The two circles represent compasses.

Diagram 2.3

(i) Draw arrows in the circles on Diagram 2.3 to represent the direction(s) of the pointers.

[2 marks]

(ii) The solenoid acts as a magnet. State the poles at R and S.Polarity at R : …………………………………Polarity at S : …………………………………

[2 marks]

Diagram 2.4

(c) Solenoid RS is now connected to a galvanometer, G as shown in Diagram 2.4. What happens if a bar magnet is pushed into the solenoid?Give reasons for your answer. ______________________________________________


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______________________________________________ [3 marks]

3 Diagram 3 shows the structure of a transformer.

Diagram 3

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

________________________________________ [1 mark]

(ii) Draw a symbol for the transformer named in 3(a)(i).

[1 mark]

(iii) State why the core is made of soft iron.

________________________________________ [1 mark]

(b) The number of turns of the primary coil is 800. Calculate the number of turns of the secondary coil.

[2 marks]

(c) The transformer is used to switch on a ticker-timer. The current flows through the primary coil is 0.25 A and the efficiency is 60%.

(i) Calculate the output power of the transformer.

[2 marks](ii) Suggest a modification to increase the efficiency

of the transformer.

________________________________________________________________________________

[1 mark]

(d) Give one reason why a radio which is connected to the output of the transformer does not function when the radio switched on.____________________________________________________________________________________________

[1 mark]

4 Table 1 shows four different coils that are used to construct transformers.

Coil Number of turns

E 50

F 200

G 1 000

H 2 000

Table 1

(a) Based on Table 1, complete Table 2 with correct pairs of coils to construct the transformers given.

Type of transformer

Primary coil Secondary coil

Step-up

Step-down

Table 2 [2 marks]

(b) Determine the pair of coils which step down the voltage from 240 V to 6 V.

[2 marks](c) Diagram 4 shows a simple transformer. When the

switch is on, the bulb lights up with normal brightness.

Diagram 4 [3 marks]

(i) Explain how the bulb lights up with normal brightness.________________________________________________________________________________________________________________________

[3 marks]

(ii) Calculate the efficiency of the transformer if the current flows in the primary coil is 0.1 A.


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[3 marks]

5 Diagram 5.1 shows a wire AB carries a constant current in the direction from A to B.

Diagram 5.1

(a) Draw the magnetic field on the horizontal surface in Diagram 5.1. Mark clearly the direction of the field.

[2 marks]

(b) Diagram 5.2 shows another wire XY which is parallel and near AB, carries current in the opposite direction to the current in AB.

Diagram 5.2 [2 marks] (i) Draw the resultant magnetic field produced by the

current XY and the current AB. [2 marks]

(ii) Label the direction of force that acts on wire AB and wire XY on the diagram in 5(b)(i).

[2 marks]

(iii) Suggest two factors that can increase the magnitude of the force between the wires AB and XY.

1._______________________________________2._______________________________________

[2 marks]

6 Diagram 6 shows the apparatus set-up which is used to study the effect of magnetic field on copper rod carrying electric current.

Diagram 6

(a) On Diagram 6, mark and label magnetic field with letter M.

[2 marks]

(b) When the switch is turned on, the copper rod is observed rolling to one side on copper track.

On Diagram 6,(i) mark and label the direction of current with letter,

I, on the copper rod. [1 mark]

(ii) mark and label the direction of force, F, that acts on the copper rod.

[1 mark](c) Explain how the movement of copper rod is produced.

__________________________________________________________________________________________________________________________________________

[3 marks]

(d) The rheostat in the circuit is adjusted so that the resistance is reduced. Explain changes made to the motion of the copper rod.____________________________________________________________________________________________

[2 marks]

7 Diagram 7.1 and Diagram 7.2 show solenoid connected to

ammeter, rheostat and d.c. power supply.


SECTION B

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Diagram 7.1 Diagram 7.2

When constant current flow in each circuit, pins are attracted to the iron core.(a) What is meant by electromagnet ?

[1 mark]

(b) Using Diagram 7.1 and Diagram 7.2, compare the number of pins attracted and the magnetic strength of the two electromagnets.

[3 marks](c) State the relationship between the magnetic strength

and(i) the number of turns of wire.

(ii) the number of pins attracted. [2 marks]

(d) Diagram 7.3 shows the use of electromagnet as a electromagnetic relay.

Diagram 7.3

Explain how the electromagnet relay is used to turn on the air conditioner.

[4 marks]

(e) Diagram 7.4 shows a d.c. electric motor which is supplied with 12 V.

Diagram 7.4

(i) Explain how the motor is able to rotate. [6 marks]

(ii) Explain the modification that is required to enable the d.c. motor to become an a.c. motor that can move faster when connected to 12 V a.c. supply.

[4 marks]

8 Diagram 8.1 and Diagram 8.2 show one magnet and two magnets are being pushed with uniform speed into the identical solenoid separately.

Diagram 8.1 Diagram 8.2(a) (i) What is meant by electromagnetic induction?

[1 mark](ii) With reference to Diagram 8.1 and Diagram 8.2,

compare the number of magnets used and the deflection of the galvanometer’s pointer. Relate the number of magnets and the deflection of the galvanometer’s pointer to make a deduction between the magnitude of current and strength of magnetic field. Name the physics law that explain 8(a)(ii).

[5 marks]

(b) Explain the advantages of the national grid system in the transmission of electricity.

[4 marks]

(c) Explain the use of transformer in reducing the power loss in the system of transmission of electric power.

[3 marks]

(d) Diagram 8.3 shows the structure of an a.c. dynamo.

Diagram 8.3

Explain clearly how it works.

[7 marks]


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9 (a) Diagram 9.1 shows the structure of a transformer.

Diagram 9.1

Explain the operating principle of a transformer. [5 marks]

(b) Diagram 9.2 shows a model of an electric transmission system in a laboratory. The model consists of a power station which generates 6 V of alternating current, a.c. transmitting the electrical energy to the users through transmission wires and transformers J, K and L.

Diagram 9.2

You are requested to set up the model as in Diagram 9.2 by using the information in Table 3.

Number of turns of the

coil

Type of metal used for the transmission wire

Type of transformer core

10 Aluminium Copper core

48 Copper Laminated copper core

50 Nichrome Soft iron core

60 Constantan Laminated soft iron core

75 Steel Steel core

360 Iron Laminated steel core

Table 3 Using the information in Diagram 9.2 and Table 3, determine:

(i) the number of turns in the primary coil and the secondary coil of transformers J, K and L.

(ii) the type of metal used for the transmission wire. Justify your choice.

(iii) the type of core used for the transformers. Justify your choice.

[10 marks](c) Electric power of 990 kW is supplied at 33 kV to a

heavy industry through cable of total resistance 100 . Calculate

(i) total loss of power from the cable due to heating effect.

(ii) efficiency of the power transmission. [5 marks]

10 Diagram 10.1 shows a bar magnet that oscillates freely. A copper coil connecting to a galvanometer is brought close to the bar magnet.

Diagram 10.1 (a) (i) What is meant by electromagnet induction?

[1 mark](ii) State the Lenz’s law.

[2 marks] (iii) Explain what happens to the copper coil when the

bar magnet oscillates and give reasons why the amplitude of the bar magnet get smaller.

[7 marks](b) Diagram 10.2 shows the transmission of electric power

to the consumers.


SECTION C

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Diagram 10.2 Table 4 shows the characteristics of four types of cables.

CableDensity/

kg m–3Resistance/

km–1 Diameter/ cmSpecific heat

capacity/J kg–1 °C–1

P 3.0 103 2.5 1.0 450

Q 5.0 103 0.8 2.0 750

R 2.0 103 0.5 4.0 1 000

S 6.0 103 1.5 3.0 200

Table 4 Explain the suitability of each characteristics of cables in Table 4 for use in the transmission of electric power. Determine the most suitable cable. Give reasons for your choice.

[10 marks]

1 A student carries out an experiment to investigate the

relationship between the number of turns in secondary coils, Ns and output voltage, Vs of a transformer.The results of the experiment are shown in the graph Vs

against Ns in Diagram 1.


PAPER 3 SECTION A SECTION B

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Diagram 1

(a) Based on the graph in Diagram 1,(i) state the relationship between Vs and Ns.

[1 mark]

(ii) determine the value of Vs when Ns = 40. Show on the graph how you determine the value

of Vs. [3 marks]

(iii) calculate the gradient of the graph, m.Show on the graph how you determine value of m.

[3 marks]

(b) Given the primary voltage is 240 V a.c., using the formula Ns / Np = Vs / Vp and the gradient, m in 1(a)(iii), calculate the number of turns in primary coil.

[2 marks]

(c) Suggest two ways that can be used to improve the efficiency of the transformer.

[2 marks]

(d) State one precaution that should be taken to improve the result of this experiment.

[1 mark]

2 Diagram 2.1 and Diagram 2.2 shows a table fan.In Diagram 2.1, the speed control is set at button 1 and the fan blade is rotating. In Diagram 2.2, the speed control is set at button 3 and the fan blade is rotating faster.

Diagram 2.1 Diagram 2.2

Based on the observation on Diagram 2.1 and Diagram 2.2 and applying your knowledge of the magnetic effect of current:(a) State one suitable inference. [1 mark](b) State one hypothesis that could be investigated. [1 mark](c) With the use of apparatus such as magnets, C-shaped

iron yoke, bare copper wire, connecting wires, d.c. power supply, ammeter and other apparatus, describe an experiment to investigate the hypothesis stated in 2(b).In your description, state clearly the following:

(i) The aim of the experiment. (ii) The variables in the experiment. (iii) The list of apparatus and materials. (iv) The arrangement of the apparatus.

(v) The procedure of the experiment which should include the method of controlling the manipulated variable and the method of measuring the responding variable.

(vi) The way you tabulate the data.(vii) The way you analyse the data.

[10 marks]


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IT Phy F5 Topical Test 3 (BI)