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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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