NIQUE SCIENCE ACADEMY - …mohammadirfan29.yolasite.com/resources/Physics Test (Unit 21-23)I.pdf · Pap er: Physics 1 Dedicated to My Son Mohammad Irtaza Zain. Code 5054 [3] 1 A transformer

Test (Unit 21-23)

:........................................................ Code: 5054 Class: CIIA

This document consists of 5 printed pages.

21 M

[Total 7]

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heory Section:

T [Total arks]

Time Allowed: 35Minutes

Maximum Marks: 25

NIQUE SCIENCE ACADEMY U

Date

Name

Paper: Physics

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Dedicated to My Son Mohammad Irtaza Zain. Code 5054

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1 A transformer has an output of 24 V when supplying a current of 2.0 A. The current in theprimary coil is 0.40 A and the transformer is 100% efficient.

(a) Calculate

(i) the power output of the transformer,

power = ..................................

(ii) the voltage applied across the primary coil.

voltage = ..................................[4]

(b) Explain

(i) what is meant by the statement that the transformer is 100% efficient,

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(ii) how the transformer changes an input voltage into a different output voltage.

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Fig. 2.1

Two coils are wound on an iron rod, as shown in Fig. 2.1. One coil is connected to a cell and a 2 (a) switch. The other is connected to a sensitive centre-zero millivoltmeter.

sensitive centre-zeromillivoltmeter

iron rod

(i) The open switch is now closed.

State what happens to

1. the iron rod,

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2. a small steel pin held close to one end of the iron rod,

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3. the needle of the millivoltmeter.

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(ii) The switch is opened again.

State what happens to the needle of the millivoltmeter.

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(b) You are given an iron bar, a length of insulated wire, a battery and a variable resistor.

You are to make an electromagnet whose strength can be varied.

(i) In the space below, draw a diagram of the electromagnet that includes the circuit. [2]

(ii) What is the setting of the variable resistor that gives the strongest magnetism of the electromagnet?

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Fig. 3.1

P and Q are placed end to end, as shown in Fig. 3.1.

3 A coil P is joined to a battery and a switch S. A similar coil Q is joined to a sensitive centre-zero millivoltmeter G.

S

P Q

G

(a) Describe what is seen happening to the reading of G

(i) as switch S is closed,

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(ii) as switch S is opened again.

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(b) A soft iron bar, as long as the combined lengths of P and Q, is placed inside P and Q.

State what difference this makes to what is observed on G as S is closed.

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(c) The bar in (b) is removed and the battery is changed for one with a smaller e.m.f.

State what difference this makes to what is observed on G as S is closed.

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(d) The battery is replaced by an a.c. power supply of frequency 50 cycles per second, and then S is closed.

Describe what is seen on G.

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Dedicated to My Son Mohammad Irtaza Zain. Code 5054 [Turn over

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4 MCQ SECTION: [Total Marks] A small coil is connected to a galvanometer G, as shown.

N

S

G

When a magnet is allowed to fall towards the coil, the galvanometer pointer gives a momentary deflection to the right of the zero position.

The magnet moves through the coil.

What happens to the galvanometer pointer as the magnet falls away from the coil?

A It gives a continuous reading to the left.

B It gives a momentary deflection to the left.

C It gives a continuous reading to the right.

D It gives a momentary deflection to the right.

The diagram shows a two-pole single-coil electric motor.

The split-ring commutator reverses the current in the coil as it rotates.

How many times is the current reversed if the coil is rotated once?

A 1 B 2 C 3 D 4

single coil

split-ring commutator

N S

+ –

Which statement about the action of a transformer is correct?

A An alternating current always flows in the secondary coil when an alternating voltage isapplied to the primary coil.

B The current in the secondary coil is always larger than the current in the primary coil.

C An e.m.f. is induced in the secondary coil when an alternating voltage is applied to theprimary coil.

D An e.m.f. is induced in the secondary coil when a steady direct current flows in the primarycoil. Irtaz

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4 A B C D

3 A B C D

2 A B C D

1 A B C D

MCQ Answer Sheet

Which transformer arrangement produces an output voltage that is larger than the input voltage?

iron core

d.c.input

output

Airon core

a.c.input

output

B

iron core

d.c.input output

Ciron core

a.c.input output

D

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