EASY

Earn 100

Explain what is emission power of a body?

Important Questions on Heat

HARD

In steady state heat conduction, the equations that determine the heat current

j (r)

[heat flowing per unit time per unit area] and temperature

T (r)

in space are exactly the same as those governing the electric field

E (r)

and electrostatic potential

V (r)

with the equivalence given in the table below.

Heat flow	Electrostatics
$T (r)$	$V (r)$
$j (r)$	$E (r)$

We exploit this equivalence to predict the rate

Q

of total heat flowing by conduction from the surfaces of spheres of varying radii, all maintained at the same temperature. If

Q \propto R^{n},

where

R

is the radius, then the value of

n

EASY

Science>Physics>Heat>Heat Transfer

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

Science>Physics>Heat>Heat Transfer

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

Science>Physics>Heat>Heat Transfer

Two identical metal wires of thermal conductivities

K_{1}

and

K_{2}

respectively are connected in series. The effective thermal conductivity of the combination is:

HARD

Science>Physics>Heat>Heat Transfer

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

EASY

Science>Physics>Heat>Heat Transfer

Prevost's theory of heat exchange is not applicable at temperature

EASY

Science>Physics>Heat>Heat Transfer

Statement $A :$ Convection involves flow of matter within a fluid due to unequal temperatures of its parts.

Statement $B :$ A hot bar placed under a running tap water loses heat due to effect of convection within water.

Statement. $C :$ Heat transfer always involves temperature difference between two systems.

EASY

Science>Physics>Heat>Heat Transfer

A piece of metal and a piece of wood are kept at a temperature of $45 ° C$ .

On touching the two with hand,

MEDIUM

Science>Physics>Heat>Heat Transfer

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

MEDIUM

Science>Physics>Heat>Heat Transfer

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

MEDIUM

Science>Physics>Heat>Heat Transfer

Two thin metallic spherical shells of radii

r_{1}

and

r_{2} (r_{1} < r_{2})

are placed with their centres coinciding. A material of thermal conductivity

K

is filled in the space between the shells. The inner shell is maintained at temperature

θ_{1}

and the outer shell at temperature

θ_{2} (θ_{1} < θ_{2}) .

The rate at which heat flows radially through the material is :

EASY

Science>Physics>Heat>Heat Transfer

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:

HARD

Science>Physics>Heat>Heat Transfer

Two rods whose lengths are

l_{1}

and

l_{2}

with heat conductivity co-efficients

k_{1}

and

k_{2}

are placed end to end. The heat conductivity coefficient of a uniform rod of length

l_{1} + l_{2}

whose conductivity is same as that of the system of these two rods is

EASY

Science>Physics>Heat>Heat Transfer

The freezer in a refrigerator is located at the top section so that

EASY

Science>Physics>Heat>Heat Transfer

Which of the following is NOT a reversible process?

EASY

Science>Physics>Heat>Heat Transfer

The wavelength of thermal radiation is

EASY

Science>Physics>Heat>Heat Transfer

A certain planet is at

a

distance

d

from the sun. Then the temperature of the planet is

HARD

Science>Physics>Heat>Heat Transfer

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

MEDIUM

Science>Physics>Heat>Heat Transfer

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

HARD

Science>Physics>Heat>Heat Transfer

A thin piece of thermal conductor of constant thermal conductivity insulated on the lateral sides connects two reservoirs which are maintained at temperatures, $T_{1}$ and, $T_{2}$ as shown. Assuming that the system is in steady-state, which of the following plots best represents the dependence of the rate of change of entropy on the ratio of temperatures, $\frac{T_{1}}{T_{2}}$

Question Image

Explain what is emission power of a body?

Important Questions on Heat

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