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Solar constant is 1370 W/m². 70% of the light incident on the earth is absorbed by the earth and the earth's average temperature is 288 K. The effective emissivity of the earth is

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Important Questions on Thermal Properties of Matter

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A heat source at

T = 10^{3} K

is connected to another heat reservoir at

T = 10^{2} K

by a copper slab which is

1 m

thick. Given that the thermal conductivity of copper is

0 .1 W K^{- 1} m^{- 1}

, the energy flux through it in the steady-state is:

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Heat energy is incident on the surface of a material at the rate of

1000 J \min^{- 1}

. If the coefficient of absorption is

0.8

and the coefficient of reflection is

0.1

, then the amount of heat energy transmitted through the material in

5 minutes

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A cylinder of radius

R

is surrounded by a cylindrical shell of inner radius

R

and outer radius

2 R

. The thermal conductivity of the material of the inner cylinder is

K_{1}

and that of the outer cylinder is

K_{2}

. Assuming no loss of heat, the effective thermal conductivity of the system for heat flowing along the length of the cylinder is:

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are $K_{1}$ and $K_{2}$ . The thermal conductivity of the composite rod will be

Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Let there be four identical cubes having colours blue, red, black and white. When they are heated together and allowed to cool under identical conditions, which cube will cool at the earliest?

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two rectangular blocks, having identical dimensions, can be arranged either in configuration

I

or in configuration

I I

as shown in the figure. One of the blocks has thermal conductivity

K

and the other

2 K

. The temperature difference between the ends along the x-axis is the same in both the configurations. It takes

9 s

to transport a certain amount of heat from the hot end to cold end in the configuration

I

. The time to transport the same amount of heat in the configuration

II

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Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Solar energy is incident normally on the earth's surface at the rate of about

1 .4 kW m^{- 2}

. The distance between the earth and the sun is

1 .5 \times 10^{11} m

. Energy

(E)

and mass

(m)

are related by the Einstein equation,

E = m c^{2}

where

c = (3 \times 10^{8} m s^{- 1})

is the speed of light in free space. The decrease in the mass of the sun is

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Three rods of identical cross-section and length are made of three different materials of thermal conductivity $K_{1}, K_{2}$ and $K_{3}$ , respectively. They are joined together at their ends to make a long rod (see figure). One end of the long rod is maintained at $100 ° C$ and the other at $0 ° C$ (see figure). If the joints of the rod are at $70 ° C$ and $20 ° C$ in steady and there is no loss of energy from the surface of the rod, the correct relationship between $K_{1}, K_{2}$ and $K_{3}$ is :

Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

In Raman effect, the spectral line with lower frequency than the incident frequency is

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

A certain planet is at

a

distance

d

from the sun. Then the temperature of the planet is

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Three rods of Copper, Brass and Steel are welded together to form a Y-shaped structure. Area of cross-section of each rod is

4 {cm}^{2}

. End of copper rod is maintained at

100 ° C

. Where as ends of brass and steel are kept at

0 ° C

. Lengths of the copper, brass and steel rods are

46, 13

and

12 cms

respectively. The rods are thermally insulated from surroundings except at ends. Thermal conductivities of copper, brass and steel are

0.92, 0.26

and

0.12

CGS units respectively. Rate of heat flow through copper rod is :

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Three large identical plates are kept parallel to each other. The outer two plates are maintained at temperatures

T

and

2 T

, respectively. The temperature of the middle plate in steady state will be close to

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The unit of thermal conductivity is

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The two ends of a metal rod are maintained at temperatures

100 ° C

and

110 ° C

. The rate of heat flow in the rod is found to be

4.0 J s^{- 1}

. If the ends are maintained at temperatures

200 ° C

and

210 ° C

, the rate of heat flow will be:

MEDIUM

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Two materials having coefficients of thermal conductivity

3 K

and

K

and thickness

d

and

3 d

respectively, are joined to form a slab as shown in the figure. The temperatures of the outer surfaces are

θ_{2}

and

θ_{1}

respectively,

(θ_{2} > θ_{1})

. The temperature at the interface is
Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Three rods of identical cross-sectional area and made from the same metal, form the sides of an isosceles triangle

A B C

right angled at

B

as shown in figure. The point

A

and

B

are maintained at temperature

T

and

\sqrt{2} T

respectively, in the steady state. Now, assuming that only heat conduction takes place. The temperature of point

C

will be

HARD

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

Consider a pair of insulating blocks with thermal resistances $R_{1}$ , and $R_{2}$ as shown in the figure. The temperature $θ$ at the boundary between the two blocks is

Question Image

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

The wavelength of thermal radiation is

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

(A)	The energy emitted versus wavelength plot of a black body depends on the material of the black body.
(B)	The emissivity of a completely reflecting surface is zero.
(C)	Emissivity is equal to ${(absorptive power)}^{2}$ .
(D)	Black-body radiates more than normal body Which of the following is correct?

EASY

Physics>Heat and Thermodynamics>Thermal Properties of Matter>Radiation

For any material, if

R, T

and

A

represent the reflection coefficient, transparent coefficient and absorption coefficient respectively, then for a blackbody which one of the following is true

Solar constant is 1370 W/m2. 70% of the light incident on the earth is absorbed by the earth and the earth's average temperature is 288 K. The effective emissivity of the earth is

Important Questions on Thermal Properties of Matter

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Solar constant is 1370 W/m². 70% of the light incident on the earth is absorbed by the earth and the earth's average temperature is 288 K. The effective emissivity of the earth is