Black body radiation question?

[vkash]

black body radiation question??

Homework Statement

Ina dark room ambient temperature T₀, black body is kept at a temperature T. keeping the temperature of the black body constant(at T), sun rays are allowed to fall on the black body through the hole in the roof of the room. assuming that there is no change in the ambient temperature of the room, which of the following statements are correct?

(a) the quantity of the radiation absorbed by the black body in unit time will increase.
(b)since emissivity = absorptivity, hence the quantity of the radiation emitted by the black body in unit time will increase
(c) Black body radiates more energy in unit times in the visible spectrum
(d) The reflected energy in unit time by the black body remains constant

Homework Equations

emissivity=absorptivity

The Attempt at a Solution

I think all the options are correct;
Now after opening the hole in the roof greater amount of heat is falling on the black body so it will absorbe greater amount of heat; since emissivity=absorptivity so it will reflect greater quantity of heat energy;
But answer is different from my htought;
can u please explain the correct answer for this question.

 

[LawrenceC]

The problem states that the body is kept at constant temperature, T, even with the hole in the roof admitting the sun's rays that are absorbed. If that is the case, radiation being emitted from the black body remains constant because radiation is only a function of temperature at constant emissivity. The additional heat is being removed by another mechanism.

A black body does not reflect. It absorbs 100% of incident thermal radiation.

Seems to me that only 'a' is true.

 

[vkash]

The problem states that the body is kept at constant temperature, T, even with the hole in the roof admitting the sun's rays that are absorbed. If that is the case, radiation being emitted from the black body remains constant because radiation is only a function of temperature at constant emissivity. The additional heat is being removed by another mechanism.

A black body does not reflect. It absorbs 100% of incident thermal radiation.
Seems to me that only 'a' is true.

No that's not correct.
I also think as u think but i was incorrect. and u are also incorrect. soon i am going to ask it to my physics teacher. In last class the i forget to ask but i will try to ask on upcoming class on Monday.

 

[LawrenceC]

No that's not correct.
I also think as u think but i was incorrect. and u are also incorrect. soon i am going to ask it to my physics teacher. In last class the i forget to ask but i will try to ask on upcoming class on Monday.

I would be interested in hearing the teacher's explanation. I am skeptical because the object's temperature remains constant so heat is leaving by another mechanism in order to maintain a steady state condition. This is entirely possible with constant ambient temperature (as the problem states) if the air movement is increased, thereby increasing heat transfer by convection.

 

[asteriatic]

I would like to clarify that the correct answer to this question is (a) the quantity of radiation absorbed by the black body in unit time will increase. This is because the black body will absorb more radiation from the sun due to the increased exposure to sunlight. This does not necessarily mean that the black body will reflect more energy, as the emissivity and absorptivity will remain the same. The black body will also not necessarily radiate more energy in the visible spectrum, as the increase in absorbed radiation may not affect the emission spectrum of the black body. It is also important to note that the ambient temperature of the room remains constant, so there will be no change in the reflected energy in unit time by the black body.