Question

A black body emits:
A. Radiations of all wavelengths
B. No radiations
C. Radiations of only one wavelength
D. Radiations of selected wavelength

Answer 1

Hint: A black body is defined as a body which absorbs all radiation and then emits continuous radiation across the whole spectrum of electromagnetic radiation. However, depending upon its temperature, it gives off the maximum amount of radiation of a specific wavelength called the peak wavelength at that temperature.

Complete Step-by-Step solution:
A black body is defined as a body which absorbs all the radiation received by it. It completely absorbs all the radiation and does not allow the radiation to reflect off it or transmit through it.
The black body then also emits this radiation energy in the form of radiation distributed continuously across all wavelengths in the electromagnetic spectrum. However, based on its temperature, the black body emits the maximum amount of radiation of a specific wavelength known as the peak wavelength, which is what the colour of the blackbody appears to us. As the temperature of the black body increases, the peak wavelength becomes smaller.
Hence, the correct option is A) radiations of all wavelengths.

Note: A perfect black body is only theoretical but has not been found or made practically. However, some stars and other celestial bodies are very close approximations for an ideal black body.
An iron rod can also be considered to be a black body to an extent. In fact, the example of an iron rod being heated in a flame gives an excellent feel for the concept of changing peak wavelength of emission with temperature of the body.
When the iron rod is heated in the flame, it slowly starts to glow (emits radiation). As the rod gets heated up and its temperature increases, it slowly starts glowing red (the peak wavelength) and with further increase in temperature, becomes blue. Thus, the peak wavelength goes on decreasing (from red to blue) as the temperature rises.