Physics 2008 | Study Mode

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Question 31

The d.c generator has essentially the same components as the a.c generator except the presence of?

slip-ring

carbon brushes

split ring

armature

Explanation

To correct and A.C generator with a D.C generator the slip ring is replaced with split-ring communicator

Correct option: C

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Question 32

A step-down transformer has a power output of 50 W and efficiency of 80%. if the mains supply voltage is 200 v, calculate the primary current of the transformer.

0.31 A

3.20 A

3.40 A

5.00 A

Explanation

Efficiency = (power output)/power input x 100%
= 1_s V_S x 100% 1_p
V_p
(80)/100 = (50)/I_P x 200
I P = (50 x 100)/80 x 200 = 3.125 A

Correct option: A

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Question 33

caesium has a work function of 3 x 10^-19J. the maximum energy of liberated electrons when it is illuminated by light of frequency 6.7 x 10¹⁴

HZ is?

[h = 6.6 x 1010^-34Js]

1.42 x 10^-19J

3.00 x 10^-19J

4.42 x 1010^-19J

7.42 x 10^-19J

Explanation

Max kinetic energy = Energy of incident electron - work function. EK = hf - w
= 6.6 x 10^-34 x 6.7 x 10¹⁴ - 3 x 10^-19
= 4.422 x 10^-19 - 3 x 10^-19
= 1.422 x 10^-19J

Correct option: A

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Question 34

zener diode is used for?

current amplification

power amplification

voltage regulation

energy conversion

Explanation

Zener diode is useful in stabilized power supply i.e to keep steady the voltage of a power supply.

Correct option: C

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Question 35

When a pure semiconductor is heated, its resistance

increases

decreases

remains the same

increases and then decreases

Explanation

Heating a pure semiconductor increases the mobility of electrons and holes and hence the conductivity. thus, the resistance decreases on heating

Correct option: B

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Question 36

I. for current amplification.

II. for voltage stabilization.

III. for power amplification.

IV. as a switch.

which of the above are the uses of transistor?

I,II,III and IV

I,III, and IV only

I, II and III only

I,II and IV only

Explanation

Transistor is used for amplification of current, power and as a switch in logic gates.

Correct option: B

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Question 37

The dimension of electromotive force are `

ML²T^-3I^-1

ML²T^-3I^-2

M²LT^-2I^-1

M²L²T^-1I^-1

Explanation

Electrical work W = QE,
Where Q is the quantity of change and E is the electromotive force.
E = W = FxDQ_It
Where D is the displacement,I = current and t = time
But dimension of force,
= unit of mass x unit of Acceleration
= unit of mass xunit of velocityunit of time
= unit of mass x unit of displacement__unit of time x unit of time
ML/T² = MLT^-2
Dimension of emf E
= MLT^-2L = ML²T^-3I^-1__IT

Correct option: A

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Question 38

The resultant of two forces 12N and 5N is 13N. What is the angle between the two forces?

0^o

45^o

90^o

180^o

Explanation

R² - P² + Q² = 12² + 5²
= 144 + 25 = 169
R = 169 = 13N
angle between the forces is 90^o Phy-explained-image

Correct option: C

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Question 39

A force F required to keep a 5 kg mass moving round a cycle of radius 3.5 m at a speed of 7 ms^-1. What is the speed, if the force is tripled?

4.0 ms^-1

6.6 ms^-1

12.1 ms^-1

21.0 ms^-1

Explanation

The force which is centripetal
F = MV²_R
=5 x 7²3.5
= 70
V = (Fr) and if F is tripped, then
V = (3Fr)/m
= (3x70x3.5)/5
= 12.1ms^-1

Correct option: C

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Question 40

A body of mass 4 kg resting on a smooth horizontal plane is simultaneously acted upon by two perpendicular forces 6N and 8N. Calculate the acceleration of the motion

2.5 ms^-1

3.0 ms^-1

4.0 ms^-1

4.5 ms^-1

Explanation

Smooth plane has negligible friction
only the resultant of the perpendicular forces is acting on the body, which is given as
F =
8² + 6²

=
64 + 36

=
100

= 10N
But F = Ma
a = ^F/_M = ¹⁰/₄ = 2.5 ms^-1

Correct option: A

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