JEE Main Physics - Transference of Heat
Exam Duration: 60 Mins Total Questions : 30
Which of the following will cool rapidly?
- (a)
A polished calorimeter filled with water at \(100ºC\)
- (b)
A polished calorimeter filled with oil at \(100ºC\)
- (c)
A black calorimeter filled with water at 100ºC
- (d)
A black calorimeter filled with oil at 100ºC
A body cools from 80°C to 50°C in 3 minutes. Calculate time it takes to cool from 60°C to 30°C if temperature of the surroundings is 20°C.
- (a)
3 minutes
- (b)
4 minutes
- (c)
5 minutes
- (d)
6 minutes
Thermal conductivity
- (a)
for a substance usually varies with temperature
- (b)
for a substance remains constant with temperature
- (c)
for a perfect thermal conductor is zero
- (d)
for a perfect thermal insulator is infinite
If temperature of a black body increases from \(7°C\) to \(287°C\), then the rate of energy radiation increases by
- (a)
\({ \left( \frac { 287 }{ 7 } \right) }^{ 4 }\)
- (b)
16
- (c)
4
- (d)
2
The maximum wavelength of radiation emitted at 200 K is 4 \(\mu m\). What will be maximum wavelength emittted at 2400 K?
- (a)
3.3 \(\mu m\)
- (b)
0.66 \(\mu m\)
- (c)
1 metre
- (d)
1 \(\mu m\)
Two rods of same length and material transfer a given amount of heat in 12s, when they are joined end to end. But when they are joined lengthwise, they will transfer same heat in same conditions in
- (a)
24 s
- (b)
3 s
- (c)
48 s
- (d)
1.5 s
Two rods of length d1 and d2 and and coefficients of thermal conductivities K1 and K2 are kept touching each other. Both have same area of cross-section; the equivalent thermal conductivity is
- (a)
\({ K }_{ 1 }+{ K }_{ 2 }\)
- (b)
\({ K }_{ 1 }{ d }_{ 1 }+{ K }_{ 2 }{ d }_{ 2 }\)
- (c)
\(\frac { { d }_{ 1 }{ K }_{ 1 }+{ d }_{ 2 }{ K }_{ 2 } }{ { d }_{ 1 }+{ d }_{ 2 } } \)
- (d)
\(\frac { { d }_{ 1 }+{ d }_{ 2 } }{ \frac { { d }_{ 1 } }{ { K }_{ 1 } } +{ \frac { { d }_{ 2 } }{ { K }_{ 2 } } } } \quad \)
During severe winter in the low temperature zones of the world, the superficial parts of the lakes are frozen, leaving water below. The freezing at the bottom is prevented because:
- (a)
the conductivity of ice is low
- (b)
the water has large specific heat
- (c)
the water has large latent heat of fusion
- (d)
the temperature of the earth at the bottom of the lake is high
Which of the following combinations of properties would be most desirable for a cooking pot?
- (a)
High specific heat and low thermal conductivity
- (b)
Low specific heat and high thermal conductivity
- (c)
High specific heat and high thermal conductivity
- (d)
Low specific heat and low thermal conductivity
If ⋋m denotes the wavelength at which the radiative emission from a black body at a temperature T K is maximum, then:
- (a)
λm ∝ T4
- (b)
λm is independent of T
- (c)
λm ∝ T
- (d)
λm ∝ T-1
A cylinder of radius R made of a material of thermal conductivity K1 is surrounded by a cylindrical shell of inner radius R and outer radius 2R made of a material of thermal conductivity K2. The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is:
- (a)
K1 + K2
- (b)
\(\frac { { K }_{ 1 }+3{ K }_{ 2 } }{ 4 } \)
- (c)
\(\frac { { K }_{ 1 }{ K }_{ 2 } }{ { K }_{ 1 }+{ K }_{ 2 } } \)
- (d)
\(\frac { 3{ K }_{ 1 }+{ K }_{ 2 } }{ 4 } \\ \)
Ice starts freezing in a lake with water at 00C when the atmospheric temperature is -10°C. If the time taken for 1 em of ice to be formed is 12 minutes, the time taken for the thickness of the ice to change from I cm to 2 cm will be:
- (a)
12 minute
- (b)
less than 12 minute
- (c)
more than 12 minute but less than 24 minute
- (d)
more than 24 minute
To a rough approximation, conductivities of metals are about
- (a)
1000 times as those of liquids and 10000 times of gases
- (b)
10 times as those of liquids and 100 times of gases
- (c)
100 times as those of liquids and 1000 times of gases
- (d)
10000 times as those of liquids and 1000 times of gases
If the temperature of the sun was to increase from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on the earth to what it was previously will be:
- (a)
4
- (b)
16
- (c)
32
- (d)
64
If the temperature of a hot body is raised by 5%, then the heat energy radiated would increase by:
- (a)
5%
- (b)
10%
- (c)
11.65%
- (d)
21.55%
A solid sphere and a hollow sphere of same material and size are heated to same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is T, then:
- (a)
the hollow sphere will cool at a faster rate for all values of T
- (b)
the solid sphere will cool at a faster rate for all values of T
- (c)
both spheres will coo 1at the same rate for all values of T
- (d)
both spheres will cool at the same rate only for small values of T
Two similar rods but of different materials are joined together end to end. The ratio of their thermal conductivities is 2: 3. The composite rod is lagged between melting ice at 00C and steam at normal pressure. The temperature of the junction will be:
- (a)
600C
- (b)
500C
- (c)
400C
- (d)
300C
In a composite rod, when two rods of different lengths and of the same area of cross-section are joined end to end, then if K is the effective coefficient of thermal conductivity, \(\frac { { l }_{ 1 }+{ l }_{ 2 } }{ K } \) is equal to:
- (a)
\(\frac { { l }_{ 1 } }{ { K }_{ 1 } } -\frac { { l }_{ 2 } }{ { K }_{ 2 } } \)
- (b)
\(\frac { { l }_{ 1 } }{ { K }_{ 2 } } -\frac { { l }_{ 2 } }{ { K }_{ 1 } } \)
- (c)
\(\frac { { l }_{ 1 } }{ { K }_{ 1 } } +\frac { { l }_{ 2 } }{ { K }_{ 2 } } \)
- (d)
\(\frac { { l }_{ 1 } }{ K_{ 2 } } +\frac { { l }_{ 2 } }{ { K }_{ 1 } } \)
If a liquid is heated in weightlessness, the heat is transmitted through:
- (a)
conduction
- (b)
convection
- (c)
radiation
- (d)
neither, because the liquid cannot be heated in weightlessness
The radiation emitted by a star A is 10000 times that of the sun. If the surface temperatures of the sun and the star A are 6000 K and 2000 K respectively, the ratio of the radii of the star A and the sun is:
- (a)
300:1
- (b)
600:1
- (c)
900:1
- (d)
1200:1
A black body at 227°C radiates heat at the rate of 7 callcm 2. At a temperature of 727°C, the rate of heat radiated in the same units will be:
- (a)
50
- (b)
112
- (c)
80
- (d)
60
Shown below are the black body radiation curves at temperatures TI and T2 (T2 > TI ). Which of the following plots is correct?
- (a)
- (b)
- (c)
- (d)
A sphere and a cube of same material and same total surface area are placed in the same evacuated space turn by turn after they are heated to the same temperature. Find the ratio of their initial rates of cooling in the enclosure.
- (a)
\(\sqrt { \frac { \pi }{ 6 } } \) : 1
- (b)
\(\sqrt { \frac { \pi }{ 3 } } \) : 1
- (c)
\(\frac { \pi }{ \sqrt { 6 } } \) : 1
- (d)
\(\frac { \pi }{ \sqrt { 3 } } \) : 1
Flash light equipped with a new set of batteries, produces bright white light. As the batteries wear out:
- (a)
the light intensity gets reduced with no change in its colour
- (b)
light colour changes first to yellow and then red with no change in intensity
- (c)
it stops working suddenly while giving white light
- (d)
colour changes to red and also intensity gets reduced
A black body emits radiations of maximum intensity for the wavelength of 5000 A when the temperature of the body is 1227°C. If the temperature of the body is increased by 1000°C, the maximum intensity would be observed at:
- (a)
1000 0A
- (b)
5000 0A
- (c)
4000 0A
- (d)
3000 0A
Two solid sphere A and B made of the same material have radii rA and rB respectively. Both the spheres are cooled from the same temperature under the conditions valid for Newton's law of cooling. The ratio of the rate of change of temperature A and B is:
- (a)
\(\frac { { r }_{ A } }{ { r }_{ B } } \)
- (b)
\(\frac { { r }_{ B } }{ { r }_{ A } } \)
- (c)
\(\frac { { r }_{ A }^{ 2 } }{ { r }_{ B }^{ 2 } } \)
- (d)
\(\frac { { r }_{ B }^{ 2 } }{ { r }_{ A }^{ 2 } } \)