Physics - Transference of Heat
Exam Duration: 45 Mins Total Questions : 30
The substance having lowest thermal conductivity is
- (a)
air
- (b)
copper
- (c)
water
- (d)
sand
All good conductors are
- (a)
good reflectors
- (b)
good radiators
- (c)
good absorbers
- (d)
(a),(b) and (c) all are correct
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
Choose the CORRECT statement
- (a)
Everybody, at whatever temperature, above absolute zero, radiates electromagnetic waves from its surface.
- (b)
The wavelength of thermal radiation does not change with temperature of the radiating body.
- (c)
The amount of radiated power increases proportionally with temperature
- (d)
The amount of radiated energy does not change with temperature
Two objects at different temperatures are placed, without touching, inside an evacuated container that has perfectly reflecting inner walls. The two objects will exchange energy by
- (a)
conduction
- (b)
convection
- (c)
radiation
- (d)
convection and radiation
Choose the correct statement
- (a)
Temperature gradient is a vector quantity
- (b)
Temperature gradient lines are lines which are perpendicular to the isothermal surfaces
- (c)
Heat transfer in solids takes place mainly by conduction
- (d)
All of the above are correct
Which of the following is the correct device for the direction of thermal radiation?
- (a)
Constant volume air thermometer
- (b)
Liquid-in-glass thermometer
- (c)
Six's maximum and minimum thermometer
- (d)
Thermocouple
A solid sphere and a hollow sphere of the same material and size are heated to the 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 cool at the same rate for all values of T
- (d)
both spheres will cool at the same rate only for small values of T
Thermal radiations are similar to
- (a)
electromagnetic waves
- (b)
cathode rays
- (c)
sound waves
- (d)
alpha rays
Ice starts forming on the surface of lake and takes 8 hours to form a layer 1 cm thick. How much time will it take to increase the thickness of layer to 2 cm?
- (a)
8 hours
- (b)
less than 8 hours
- (c)
between 8 to 16 hours
- (d)
more than 16 hours
If the temperature of a black body is increased by 50%, then the amount of radiant energy given out
- (a)
increases by 50%
- (b)
increases by 500%
- (c)
increases by 400%
- (d)
increases by 125%
In which process, the rate of transfer of heat is fastest:
- (a)
Conduction
- (b)
Convection
- (c)
Radiation
- (d)
in all the cases, heat is transferred with the same velocity
If the temperature of a black body is doubled, the wavelength at which the spectral radiancy has its maximum, is
- (a)
doubled
- (b)
halved
- (c)
quadrupled
- (d)
unchanged
An ideal black-body at room temperature is thrown into a furnace. It is observed that
- (a)
initially it is the darkest body and at later times the brightest
- (b)
it is the darkest body at all times
- (c)
it cannot be distinguished at all times
- (d)
initially it is the darkest body and at later times it cannot be distinguished
A bucket full of hot water is kept in a room and it cools from 75° C to 70°C in T1 minutes, from 70° C to 65°C in T2 minutes and from 65°C to 60°C in T3 minutes. Then:
- (a)
T1 = T2 = T3
- (b)
T1 < T2 < T3
- (c)
T1 > T2 > T3
- (d)
T1 < T2 > T3
A red glass piece is heated until it glows in dark. The colour of the glow will be:
- (a)
red
- (b)
orange
- (c)
green
- (d)
violet
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
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
Which of the following is the example of an ideal black body?
- (a)
Kajal
- (b)
Black board
- (c)
A pin hole in a box
- (d)
None of these
A wire is heated gradually; as temperature rises, at first it appears:
- (a)
red
- (b)
green
- (c)
yellow
- (d)
white
Thermal radiations are electromagnetic waves belonging to:
- (a)
ultraviolet region
- (b)
visible region
- (c)
gamma region
- (d)
infrared region
A planet radiates heat at a rate proportional to the fourth power of its surface temperature T. If such a steady temperature of the planet is due to an exactly equal amount of heat received from the sun then which of the following statement is true?
- (a)
The planet's surface temperature varies inversely as the distance of the sun.
- (b)
The planet's surface temperature varies directly as the square of its distance from the sun.
- (c)
The planet's surface temperature varies inversely as the square root of its distance from the sun.
- (d)
The planet's surface temperature is proportional to the fourth power of its distance from the sun.
A planet is at an average distance d from the sun and its average surface temperature is T. Assume that the planet receives energy only from the sun and loses energy only through radiation from its surface. Neglect atmospheric effects. 1f T ∝ d-n , the value of n is:
- (a)
2
- (b)
1
- (c)
1/2
- (d)
1/4
Two rods of same material have same length and area. The heat ΔQ flows through them for 12 minutes when they are joint side by side. If now both the rods are joined in parallel, then the same amount of heat ΔQ will flow in:
- (a)
24 min
- (b)
3 min
- (c)
12 min
- (d)
6 min
Solar pond is a device for collecting solar heat. The pond is about one metre deep, filled with saturated salt solution and protected from air current and other disturbances. When exposed to the sun, the temperature at the bottom can go as high as 800eor more. Why is this possible?
- (a)
Due to convection, the heated water goes down.
- (b)
Density gradient prevents convection currents.
- (c)
Thermal conductivity of salt is very high.
- (d)
Thermal conductivity of water is very low