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Important questions on Radiation

HARD

If the temperature of a hot body is increased by 50% then the increase in the quantity of emitted heat radiation will be

A

125%

B

200%

C

300%

D

400%

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HARD

The solar constant for the earth is . The surface temperature of the sun is . The sun subtends an angle at the earth.

This question has multiple correct options
A

B

C

D

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HARD

Compare rate of radiation of metal sphere at annd .

A

0.7 : 1

B

3 : 1

C

63 : 1

D

5.063 : 1

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HARD

Rate of emission thermal radiation of a spherical black body of radius is . It rate of cooling is . Then 

A

B

C

D

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HARD

A leaf of area and mass directly faces the sun on a clear day. The leaf has an emissivity of and a specific heat of (a) Estimate the rate of rise of the leaf's temperature. (b) Calculate the temperature the leaf would reach if it lost all its heat by radiation ( the surrounding are at ). (c) In what other ways can the heat be dissipated by the leaf?

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HARD

Two spheres of same radius have their densities in the ratio and the ratio of their specific heats are . If by radiation their rates of fall of temperature are same, then find the ratio of their rates of losing heat.

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HARD

A body of area and mass directly faces the sun on a clear day. The body has an emissivity of 0.8 and specific heat of 0.8 cal/kg K. The surroundings are at . (solar
constant = 1.4 kW/).

     The temperature that the body would reach if it lost all its heat by radiation is

A

396 K

B

C

D

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HARD

Two bodies and have thermal emissivities of and , respectively. The outer surface areas of the two bodies are the same. The two bodies emit total radiant power of the same rate. Wavelength corresponding to maximum spectral radiancy in the radiation from shifted from the wavelength corresponding to maximum spectral radiancy in the radiation from , by . If the temperature of is .

This question has multiple correct options
A

The temperature of is

B

C

The temperature of is

D

The temperature of is

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HARD

and are teo isolated spheres kept in close proximity so that they can exchange energy by radiation. The two spheres have identical physical dimensions but the surface of behaves like a perfectly black body while the surface of reflects 20% of all the radiations it receives. They are isolated from all other sources of radiation. 

A

If they are in thermal equilibrium and exchange equal amounts of radiation per second, they will be at the same absolute temperature, .

B

If they are in thermal equilibrium and exchange equal amounts of radiation per second, then .

C

If they are not in thermal equilibrium and are each at at the same temperature then sphere will lose thermal energy and will gain thermal energy.

D

If they are not in thermal equilibrium and are each at at the same temperature , then the sphere will gain thermal energy and will lose thermal energy.

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HARD

Radiation emitted from a radioactive element, of half life period of min, are measured by a Geigar - Mullar counter. The count rate of the sample reduces to disintegrations /sec. in . then the initial count rate in disintegration/sec is :-

A

B

C

D

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