A body cools from 50°C to 46°C in 5 minutes and to 40°C in the next 10 minutes. The surrounding temperature is
30°C
28°C
36°C
32°C
According to Wien’s law
λm T = constant
constant
constant
T + λm = constant
A black body is at 300 K. It emits energy at a rate which is proportional to
(300)
(300)2
(300)4
(300)3
Which of the following will radiate heat to large extent?
Rough surface
Polished surface
Black rough surface
Black polished surface
The rate of radiation of black body at 0°C is E watt. The n the rate of radiation of this black body at 273°C will be
16 E
8 E
4 E
E
A black body radiates energy at the rate of E watt m– 2 at a temperature of T Kelvin. When the temperature is reduced to T/2 Kelvin, the radiant energy will become
None of the above
Woolen clothes keep the body warm, because wool
Is a bad conductor
Increases the temperature of body
Decreases the temperature
All of these
The good absorber of heat are
Non-emitter
Poor-emitter
Good-emitter
Highly polished
The maximum energy in the thermal radiation from a hot source occurs at a wavelength of 11 × 10–5 cm. according to Wien’s law, the temperature of the source (on Kelvin scale) will be n times the temperature of another source on (Kelvin scale) for which the wavelength at a maximum energy is 5.5 × 10–5 cm. The value of n is
2
4
1/2
1
Two sphere of the same material have radii 1 m and 4 m and temperature 4000 K and 2000 K respectively. the energy radiated per second by the first sphere is
Greater then by the second
Less than that by the second
Equal in both cases
The information is incomplete to draw and conclusion
A surface at temperature T0 °K receives power P by radiation from a small sphere at temperature T >> T0 and at a distance d. If both T and d are doubled, the power received by surface will becomes approximately
P
2 P
4 P
16 P
If temperature of a black body increases from 7°C to 287°C, then the rate of energy radiation becomes
16 times
4 times
2 times
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
t1 – t2 = t3
t1 < t2 < t3
t1 > t2 > t3
t1 < t2 > t3
The velocity with which thermal radiation travels in vacuum is
3 × 106 m/s
3 × 107 m/s
3 × 108 m/s
3 × 10–16 m/s
In which process the rate of transfer of heat is maximum?
Conduction
Convection
Radiation
In all these heat is transferred with the same velocity
A body cools from 60°C to 50°C in 10 minutes. If the room temperature is 25°C and assuming Newton’s law of cooling to hold good, the temperature of the body at the end of the next 10 minutes will be
38.5°C
40°C
42.85°C
45°C
Two spheres made of same material have radii in the ratio 2:1. if both the spheres are at same temperature, then what is the ratio of heat radiation energy emitted per second by them?
1: 4
4: 1
3: 4
4: 3
Solar radiation emitted by sun resembles that emitted by a black body at a temperature of 6000 K. maximum intensity is emitted at a wavelength of about 4800 A°. if the sun were cooled down from 6000 K to 3000 K, then the peak intensity would occur at a wavelength of
4800 A°
9600 A°
2400 A°
19200 A°
A perfectly black body emits radiation at temperature T1 K. If it is to radiate 16 times this power, its temperature T2. will be
T2 = 16 T1
T2 = 8 T1
T1 = 4 T1
T2 = 2 T1
Unit of Stefan’s constant is given by
W/ m K2
W/ m2 K2
W2/ m2 K4
W/ mK
A black body at hot temperature at 227°C radiates heat at a rate of 5 cal/cm2 s. at a temperature of 727°C the rate of heat radiated per unit area will be
50 cal/cm2 s
250 cal/cm2 s
80 cal/cm2 s
100 cal/cm2 s
According to Kirchhoff’s law of radiation which of the following relation is correct
Eb = Ea
Eb = E2a
Eb = E – a
A person with dark skin as compared to a person with white skin will experience
Less heat and less cold
More heat and more cold
More heat and less cold
Less heat and more cold.
For which of the following process, the thermal conduction is maximum?
constant
constant
