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Two bodies of equal mass m are heated at a uniform rate under identical conditions. Their change in temperatures are shown. Then

(i) the ratio of melting points of the substances is 1.5
(ii) the ratio of their latent heats is $0.75$
(iii) the ratio of specific heat of two substances is $0.33$ in solid-state
(iv) the ratio of specific heat of two substances is 2 in a liquid state.

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Important Questions on Thermal Properties of Matter

EASY

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

Heat required to melt $1 g$ of ice is $80 cal$ . A man melts $60 g$ of ice by chewing in one minute. His power is______

HARD

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

A thermally insulated cubical box of side length $20 cm$ and wall thickness $2 cm$ containing $2 kg$ of ice is closed on all sides. The mass of ice melted in $10$ hours is (Thermal conductivity of the material of the box $= 0.01 {Wm}^{- 1} K^{- 1},$ latent heat of ice $= 360 \times 10^{3} J {kg}^{- 1}$ and ambient temperature $= 40 ° C$ )

EASY

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

Two systems are in thermal equilibrium. The quantity which is common for them is

EASY

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

A piece of ice falls from a height

h

so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of

h

is:
(Latent heat of ice is

3.4 \times 10^{5} {J kg}^{- 1}

and

g = 10 {N kg}^{- 1}

)

MEDIUM

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

1 kg

of water, at

20 ° C

is heated in an electric kettle whose heating element has a mean (temperature averaged) resistance of

20 Ω .

The rms voltage in the mains is

200 V

. Ignoring heat loss from the kettle, time taken for water to evaporate fully is close to
[ Specific heat of water

= 4200 J {kg}^{- 1} ° C^{- 1}

Latent heat of water

= 2260 k J k g^{- 1}

]

EASY

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

The physical quantity that determines whether or not a given system

A

is in thermal equilibrium with another system

B

is called

HARD

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

10 H

inductor carries a current of

20 A

. If the energy stored in this inductor melts ice at

0 ° C,

then the mass of the ice melted is

[

Latent heat of ice

= 2.26 \times 10^{3} J {kg}^{- 1}]

MEDIUM

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

Water of volume 2 L in a closed container is heated with a coil of 1 kW. While water is heated, the container loses energy at a rate of 160 J/s. In how much time will the temperature of water rise from 27^oC to 77^oC ? (Specific heat of water is 4.2 kJ/kg and that of the container is negligible).

MEDIUM

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

Steam at

100^{o} C

is passed into

20 g

of water at

10^{o} C .

When water acquires a temperature of

80^{o} C,

the mass of water present will be:
[Take specific heat of water

= 1 c a l g^{- 1 o} C^{- 1}

and latent heat of steam

= 540 c a l g^{- 1}]

EASY

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

Latent heat of vaporisation of water is

22.6 \times 10^{5} J {kg}^{- 1}

. The amount of heat needed to convert

100 kg

of water into vapour at

100 ° C

HARD

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

A water cooler of storage capacity

120

litres can cool water at constant rate of

P

W

. In a closed circulation system (as shown schematically in the figure), the water from the cooler is used to cool an external device that generates constantly

3

kW

of heat (thermal load). The temperature of water fed into the device can not exceed

30^{o} C

and the entire stored

120

litres of water is initially cooled to

10^{o} C

. The entire system is thermally insulated. The minimum value of

P

(in

W

) for which the device can be operated for

3

hours is:

(Specific heat of water is

4.2 kJ

k g^{- 1} K^{- 1}

and the density of water is

1000 kg m^{- 3}

)

EASY

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

A closed bottle containing water at

30^{o} C

is open on the surface of the moon. Then-

MEDIUM

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

An experiment takes

10 \min

to raise the temperature of water in a container from

0^{o} C

100^{o} C

and another

55 \min

to convert it totally into steam by a heater supplying heat at a uniform rate. Neglecting the specific heat of the container and taking specific heat of the water to be

1 cal {(g^{\circ} C)}^{- 1}

, the heat of vaporization according to this experiment will come out to be:

EASY

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

If pressure increased on a piece of wax, the melting point of wax

EASY

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

Two moles of oxygen is mixed with eight moles of helium. The effective specific heat of the mixture at constant volume is

HARD

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

A current carrying wire heats a metal rod. The wire provides a constant power

(P)

to the rod. The metal rod is enclosed in an insulated container. It is observed that the temperature

(T)

in the metal rod changes with time

(t)

as:

T (t) = T_{0} (1 + β t^{\frac{1}{4}})

, where

β

is a constant with appropriate dimension while

T_{0}

is a constant with dimension of temperature. The heat capacity of the metal is:

EASY

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

200 g

water is heated from

40^{o} C

60^{o} C

. Ignoring the slight expansion of water, the change in its internal energy is close to (Given specific heat of water

= 4184

J {kg}^{- 1} K^{- 1}

MEDIUM

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

50 g

of ice at

0 ° C

is mixed with

50 g

of water at

80 ° C

. If the latent heat of ice is

80 cal g^{- 1}

and specific heat of water is

1 cal g^{- 1} ° C^{- 1}

, then the final temperature of mixture is

MEDIUM

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

A thermally insulated vessel contains

150 g

of water at

0 ° C

. Then the air from the vessel is pumped out adiabatically. A fraction of water turns into ice and the rest evaporates at

0 ° C

itself. The mass of evaporated water will be closest to: (Latent heat of vaporization of water

= 2.10 \times 10^{6} J k g^{- 1}

and Latent heat of Fusion of water

= 3.36 \times 10^{5} J k g^{- 1}

)

EASY

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

In an experiment, a sphere of aluminium of mass

0.20 kg

is heated up to

150 ° C

. Immediately, it is put into water of volume

150 cc

27^{o} C

kept in a calorimeter of water equivalent to

0.025 kg

. The final temperature of the system is

40^{o} C

. The specific heat of the aluminium is(take

4.2 Joule = 1 calorie

)

Important Questions on Thermal Properties of Matter

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