Physics Test 201

Result

Physics Test 201

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Question 1
4 / -1

In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer-

Assertion(A): In a meter bridge, if its wire is replaced by another wire having same length, made of same material but having twice the cross-sectional area, the accuracy decreases.

Reason(R): If its wire is replaced by another wire of same material, having same cross-sectional area but of twice the length, accuracy increases.

A
Both Assertion and Reason are true and Reason is the correct explanation of assertion.

B
Both Assertion and Reason are true and Reason is not the correct explanation of assertion

C
Assertion is true but Reason is false.

D
Assertion is false but Reason is true.
Question 2
4 / -1

In a nuclear reactor heavy water is used as a

A
Moderator

B
Fuel

C
Shield

D
None

Solution

Heavy water is used in certain types of nuclear reactors, where it acts as a neutron moderator to slow down neutrons so that they are more likely to react with the fissile uranium-235 than with uranium-238, which captures neutrons without fissioning.
Question 3
4 / -1

A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is

A
∞

B
3 m

C
6 m

D
4 m

Solution

We need to block the light rays using the disc till total internal reflection takes place.

As shown in figure, the direction of light ray at the edge of disc is parallel to light surface, when the incident ray makes critical angle

After the edge, light rays will be reflected due to total internal reflection and the whole radiation from light source is blocked

Hence the angle i shown in figure should be critical angle.

For critical angle we have, sin i = 1/μ = 3/5

hence tan i = 3/4 ....(1)

From figure, we see tan i = r/4 ....(2)

hence from (1) and (2), the required radius = 3 m
Question 4
4 / -1

In the following question, a Statement of Assertion (A) is given followed by a corresponding Reason (R) just below it. Read the Statements carefully and mark the correct answer-

Assertion(A): Torque is an axial vector and directed along the axis of rotation.

Reason(R): Torque is equal to vector product of force to the position vector.

A
Both Assertion and Reason are true and Reason is the correct explanation of assertion.

B
Both Assertion and Reason are true and Reason is not the correct explanation of assertion

C
Assertion is true but Reason is false.

D
Assertion is false but Reason is true.
Question 5
4 / -1

In order to double the frequency of the fundamental note emitted by a stretched string, the length is reduced to 3/4 th of the original length and the tension is changed. The factor by which the tension is to be changed is

A
3/8

B
2/3

C
8/9

D
9/4
Question 6
4 / -1

Three sound waves of equal amplitudes have frequencies v − 1 , v , v + 1. They superpose to give beats. The number of beats produced per second will be-

A
4

B
3

C
2

D
1

Solution

p1 =po sin 2π(x- 1)t

p2 =po sin 2π(x)t

p3 =po sin 2π(x+ 1)t

p=p1+p3+p2

=posin2π(x-1)t +po sin 2π(x+1)t +po sin 2π(x)t

= 2posin2πxtcos2πt +posin2πxt

= 2posin2πxt[2cos πt +1]

⇒ fbeat = 2
Question 7
4 / -1

70 calories of heat are required to raise the temperature of 2 moles of an ideal gas at constant pressure from 30^oC to 35^oC. The amount of heat required to raise the temperature of the same sample of the gas through the same range at constant volume is nearly (Gas constant = 1.99 cal/K-mole)

A
30 cal

B
50 cal

C
70 cal

D
90 cal
Question 8
4 / -1

Water is flowing on the blades of a turbine at a rate of 100 kg-s^-1 from a certain spring. If the height of the spring be 100 m, then power transferred to the turbine will be

A
0.1 kW

B
1 kW

C
10 kW

D
100 kW

Solution

Work done = Force X Distance.

From the question :

Force = 100 X 10 = 1000N

Distance = 100m

Work done = 100 X 1000 = 100000Joules

Power = Work done / Time

The time = 1 second.

Power = 100000/1 = 100000 Watts

= 100kW
Question 9
4 / -1

If the two slits in Young's experiment have width ratio 1:4, the ratio of intensity at maxima and minima in the interference pattern in

A
3 : 1

B
1 : 3

C
9 : 1

D
1 : 9

Solution
Question 10
4 / -1

Eight negative charges each of value q coulomb are placed at the corners of a cube of side 'a' metre, at the centre of which a positive charge of +2q coulomb is placed.

Q. The central charge 2q makes 8 similar pairs with the charges at corners. Their potential energy is :

A

B

C

D
none