26254.Heat energy received by the earth from the sun is due to
Convection
Radiation
Reflection of light
Transmission of light
26255.Two stars A and B radiate maximum energy at 3600Å and 3600Å respectively. Then the ratio of absolute temperatures of A and B is
256: 81
81: 256
3: 4
4: 3
26256.In which process the rate of transfer of heat is maximum?
Conduction
Convection
Radiation
In all these heat is transferred with the same velocity
26257.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 Å. if the sun were cooled down from 6000 K to 3000 K, then the peak intensity would occur at a wavelength of
4800 Å
9600 Å
2400 Å
19200 Å
26260.The earth intercepts approximately one billionth of the power radiated by the sun. if the surface temperature of the sun were to drop by a factor of 2, the average radiant energy incident on earth per second would reduce by factor of
2
4
8
16
26261.If the temperature of the sun is doubled. The rate of energy received on the earth will be increased by a factor of
2
4
8
16
26262.A body in a room cools from 90°C to 80°C in 5 minutes. the time taken to cool from 70°C to 60°C is
Less than 5 minute
5 minute
More than 5 minutes
Less or more than 5 minutes depending upon the nature of the body
26263.The process of heat transfer in which heat is transferred with actual migration of medium particles is known as
Conduction
Convection
Radiation
Reflection
26264.According to Kirchhoff’s law of radiation which of the following relation is correct
$E_{b}=E_{a}$
$E_{b}=\dfrac{E}{a}$
$E_{b}=E^{2}a$
$E_{b}=E-a$
26265.A cup of tea cools from 80°C to 60°C in one minute. The ambient temperature is 30°C. in cooling from 60°C to 50°C, it will take.
50 sec
90 sec
60 sec
30 sec
26266.Spectrum of a perfectly black body is
Line spectrum
Band spectrum
Continuous spectrum
None of these
26267.An object is at the temperature of 400°C. at what temperature would it radiant energy twice as first? The temperature of surrounding may be assumed to be negligible
200°C
200 K
800°C
800 K
26268.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
26269.The temperature of a furnace is 2327°C and the intensity is maximum in its radiation spectrum at 1200Å. If the intensity in the spectrum of a star is maximum at 4800Å, then the surface temperature of the star is
6500 K
6000 K
4800 K
7500 K
26270.Two bodies A and B at temperatures T1 K and T2K respectively have the same dimensions. Their emissivities are in the ratio of 1: 3. if they radiate the same amount of heat per unit time, then the relation between their temperatures is given by
$\dfrac{T_{1}}{T_{2}}=\dfrac{1}{3}$
$\dfrac{T_{1}}{T_{2}}=\dfrac{81}{1}$
$\dfrac{T_{1}}{T_{2}}$=31/4:1
$\dfrac{T_{1}}{T_{2}}$=91/4:1
26271.A metal piece heated to $T_{1}$K. The temperature of the surrounding is $T_{2}$K. the heat in the surrounding due to radiation is proportional to
$(T_1^4-T_2^4)$
$(T_{1}-T_{2})^{4}$
$(T_1^4+T_2^4)$
$(T_1^3-T_2^3)$
26272.The velocity with which thermal radiation travels in vacuum is
3 × $10^{6}$ m/s
3 × $10^{7}$ m/s
3 × $10^{8}$ m/s
3 × $10^{-16}$m/s
26273.A body at high temperature T K radiates heat at rate proportional to
$T^{4}$
$T^{-4}$
T
$T^{2}$