Question

In a dark room with ambient temperature $T_{0}$, a black body is kept at a temperature $T$. Keeping the temperature of the black body constant (at $T$), sunrays are allowed to fall on the black body through a hole in the roof of the dark room. Assuming that there is no change in the ambient temperature of the room, which of the following statement(s) is/are correct?

• A. The quantity of radiation absorbed by the black body in unit time will increase.
• B. Since emissivity = absorptivity, the quantity of radiation emitted by black body in unit time will increase.
• C. Black body radiates more energy in unit time in the visible spectrum.
• D. The reflected energy in unit time by the black body remains the same.

Answer 1

Answer: (A), (B), (C), (D)

Since sunrays fall on the black body, it absorbs more radiation, and since its temperature is constant, it also emits more radiation. Also, sun light is treated as white light, which comprises of all wavelengths (VIBGYOR) in the visible spectrum. Hence, it radiates more energy in the visible spectrum.