﻿ Engineering Entrance Exam Question and Answers | Thermal Properties of Matter - Zigya

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# Thermal Properties of Matter

#### Multiple Choice Questions

1.

A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is

• E/c

• 2E/c

• Ec
• Ec

B.

2E/c

Initial momentum of surface
pi = E/c
where c = velocity of light (constant)
Since, the surface is perfectly so, the same momentum will be reflected completely
Final momentum
pf= E/c
therefore
Change in momentum
∆p = pf − pi
= -E/c - E/c = -2E/c
Thus, momentum transferred to the surface is
∆p' = |∆p| = 2E/c

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2.

Two rigid boxes containing different ideal gases are placed on a table. Box A contains one mole of nitrogen at temperature T0, while Box B contains one mole of helium at temperature (7/3) T0. The boxes are then put into thermal contact with each other and heat flows between them until the gases reach a common final temperature. (Ignore the heat capacity of boxes). Then, the final temperature of the gases, Tf, in terms of T0 is

D.

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3.

The temperature of two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x, respectively are T2 and T1 (T2 > T1). The rate of heat transfer through the slab, in a steady state is with f, equal to

• 1

• 1/2

• 2/3

• 2/3

D.

2/3

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4.

Assuming the sun to be a spherical body of radius R at a temperature of T K, evaluate the total radiant power, incident on Earth, at a distance r from the Sun.

where r0 is the radius of the Earth and σ is Stefan’s constant

C.

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5.

A light ray is incident perpendicular to one face of a 90° prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45°, we conclude that the refractive index n

• n<2

B.

Angle of incidence i > C for total internal reflection.
Here i = 45° inside the medium. ∴ 45° > sin−1 (1/n)
⇒ n > √2.

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6.

If the temperature of the sun were to increase from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on earth to what it was previously will be

• 4

• 16

• 32

• 32

D.

32

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7.

The figure shows a system of two concentric spheres of radii r1 and r2 and kept at temperatures T1 and T2 respectively. The radial rate of flow of heat in a substance between the two concentric sphere is proportional to

C.

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8.

One end of a thermally insulated rod is kept at a temperature T1 and the other at T2. The rod is composed of two sections of lengths

• (k2

• (k2

• (k1

• (k1

C.

(k1

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9.

A heater coil is cut into two equal parts and only one part is now used in the heater. The heat generated will now be

• doubled

• four times

• one fourth

• one fourth

A.

doubled

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10.

Time taken by a 836 W heater to heat one litre of water from 10°C to 40°C is

• 50 s

• 100 s

• 150 s

• 150 s

C.

150 s

Let time taken in boiling the water by the heater is t sec. Then
Q = ms ∆ T

309 Views