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Published on: 20/08/2019
Thermal Properties of Matter
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Questions + Answers key
Take MCQ Physics Test
1.
Express 60°C in 0F
2.
Why two layers of cloth of equal thickness provide warmer coucring than a single layer of cloth double thickness ?
3.
Which of two has larger value of specific heat - sand or water ?
4.
White clothes are more comfortable in summer while colourful clothes are more comfortable in winter. Why ?
5.
If all the objects radiate electromagnetic energy, why do not the objects around us in everyday life become colder and colder?
6.
Does the boiling point of water change with pressure ?
7.
Black body radiation is white. Comment.
8.
Why, water is used as an coolant in the radiator of cars?
9.
The density of mercury is \(13.6\times { 10 }^{ 3 }Kg\quad { m }^{ -3 }\) at 0o C and its coefficient of volume expansion is \(1.82\times { 10 }^{ -4 }{ K }^{ -1 }\) . Find the density at 50o C.
10.
By how much the temperature of a copper rod to be raised so as to increase its length by 1% ? Given that coefficient of linear expansion of copper = 1.7 x 10-5 K-1 .
11.
An ice box is built of wood 1.75 cm thick lined inside with cork 2 em thick. If the temperature of the inner surface of the cork is 0°C and that of the outer surface of the wood is 12°C, what is the temperature of the interface ? The thermal conductivity of wood is 0.0006 and that of cork is 0.00012 CGS units
12.
A circular disc made by iron is rotating about its axis of rotation with a uniform angular speed \(\omega \)
Determine the change in the linear speed of particle at the rim in percentage. The disc of rim is slowly heated from 20o C to 50o C keeping the angular speed uniform. Give that coefficient of linear expansion for the material of iron is \(1.2\times 10^{ -5\quad }\)\(^{0}\)C-1
13.
The tungston filament of an electric lamp has a length of 0.25 m and a diameter of 6 x 10-5 m. The power rating of the lamp is 100 W. If the emissivity of the filament is 0.8, estimate the steady temperature of the filament. Stefan's constant = 5.67 x 10-8 W/m2/k4
14.
Two vessels A and B of different materials but having identical shape, size and wall thickness are filled with ice and kept at the same place. Ice melts at the rate of 100 g min-1 and 150 gmin-1 in A and B respectively. Assuming that heat enters the vessels through the walls only, calculate the ratio of thermal conductivities of their materials.
15.
A box having total surface area 0.05 m2 and of 6 mm thick side walls is filled with melting ice and kept in room. Calculate the thermal conductivity of the box material if 0.5 kg of ice melts in 1 h. The room temperature is 40o C and latent heat of fusion of ice = \(3.33\times { 10 }^{ 5 }J{ kg }^{ -1 }\)
16.
The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if
the masses of the liquids are equal
equal masses of the liquids at the same temperature are taken
different volumes of the liquids at the same temperature are taken
equal volumes of the liquids at the same temperature are taken
17.
The scale on a steel meter rod is calibrated at 20°C. What will be the error in the reading of 50 ern at 27°C? Take, a = 1.2 x 10.5 °C-1
0.042CM
0.0042
0.021 CM
0.0021 CM
18.
Dimensional formula of specific heat capacity is
[ML2T-2L-1]
[MLT-2K-1]
[M0L2T-2K-1]
[ML2T-2K]
19.
At about 4°C, a certain amount of water has maximum
energy
specific heat
density
Volume
1.
\(\frac { 9 }{ 5 } \times 60+32=140^{ 0 }F\)
2.
This is because the air enclosed between the two layers of cloth acts as a good heat insulator
3.
Water
4.
White clothes absorb very little heat radiation and keep Coloured clothes absorb almost whole of the incident radiation and keep the body warm in winter.
5.
According to the principal of heat exchanges, all the objects (above 0 K) not only radiate electromagnetic energy but also absorb at the same rate from their surroundings. Thus they do not become colder.
6.
The boiling point of water increases with the increase in pressure ( and vice-versa).
7.
The statement is true. A black body absorbs radiations of all wavelengths. When heated to a suitable temperature, it emits radiations of all wavelengths. Hence, a black body radiation is white.
8.
Because, specific heat of water is very high due to this it absorbs, a large amount of heat. This helps in maintaining the temperature of the engine low.
9.
\(13.47\times { 10 }^{ 3 }Kg\quad { m }^{ -3 }\)
10.
588.2o C
11.
Let a be the temperature of the interface in the steady state. Since the same amount of heat must flow through wood and cork, we have
\(\frac { { k }_{ 1 }A(12-a) }{ { l }_{ 1 } } =\frac { { k }_{ 1 }A(a-0) }{ { l }_{ 2 } } \)
where l1 and l2 are the thicknesses of wood and cork respectively. Their respective conductivities are kl and k2 (Fig.).
Substituting the values we get
\(\frac { 6\times { 10 }^{ -1 } }{ 1.75 } \times \left( 12-a \right) =\frac { 12\times { 10 }^{ 5 } }{ 2 } \times a\)
or 12 - a = 1.75a x 10-1
or \(a=\frac { 12 }{ 1.175 } =10.2\)0C
12.
3.6 x 10-2
13.
A = \(\pi\)r2
= 3.14 x (3 x 10-5)2
= 3.14 x 9 x 10-10 m2
According to stefan law
H = A\(\varepsilon \)\(\sigma\)T4
T4 = \(\frac { H }{ A\varepsilon \sigma } \)
T4 = \(\frac { 100 }{ 3.14\times 9\times { 10 }^{ -10 }\times 0.8\times 5.67\times { 10 }^{ -8 } } \)
\(\therefore\) T = 2616 k
Hence the steady temperature of the filament is 2616 K
14.
Let m1 and m2 be the masses of ice melted in same time (t = 1 min) in vessels A and B respectively.
Then, the amounts of heat flowed into the two vessels will be
\({ Q }_{ 1 }=\frac { { K }_{ 1 }A({ T }_{ 1 }-{ T }_{ 2 })t }{ x } ={ m }_{ 1 }L ....(i)\)
\({ Q }_{ 2 }=\frac { { K }_{ 2 }A({ T }_{ 1 }-{ T }_{ 2 })t }{ x } ={ m }_{ 2 }L ...(ii)\)
where, L is latent heat of ice.
Dividing Eq. (i) by Eq.(ii), we get,
\(\frac { { K }_{ 1 } }{ { K }_{ 2 } } =\frac { { m }_{ 1 } }{ { m }_{ 2 } } =\frac { 100g }{ 150g } =\frac { 2 }{ 3 } =2:3\)
15.
0.42 W m-1K-1
16.
(d)
equal volumes of the liquids at the same temperature are taken
17.
(b)
0.0042
18.
(c)
[M0L2T-2K-1]
19.
(c)
density
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