Question

Three objects colored black , grey and white can withstand hostile conditions up to ${2800^0}C$. These objects are thrown into furnace where each of them attains a temperature of ${2000^0}C$, which object will grow brightest?
${\text{A}}{\text{. the white object}} \\\ {\text{B}}{\text{. the black object }} \\\ {\text{C}}{\text{. all glow with equal brightness}} \\\ {\text{D}}{\text{. gray object}} \\\$

Answer 1

Hint: To answer this question we have to understand the concept An ideal black body absorbs all the radiation incident upon it and has an emissivity equal to 1. If a black is kept at the same temperature, then the black body will radiate maximum power. Hence, the black object at a temperature of 2000 °C will glow brightest.

Complete step-by-step answer:

Kirchoffs’s law:

Kirchoff's law of thermal radiation states that for a body of any arbitrary material emitting and absorbing thermal electromagnetic radiation at every wavelength in thermodynamic equilibrium, the ratio of its Emissive power to its sizeless absorption coefficient is equal to the uniform feature of radiative wavelength and temperature only. The fundamental function describes the emissive force of the perfect black body.

According to the radiation law of Kirchhoff a body which exhibits a greater absorptivity at a given temperature must also exhibit a more intense emission.
Black objects absorb maximum and can also emit maximum.

Hence option B is the correct option.

Note: Whenever we get this type of question the key concept of solving is we have to understand kirchoff’s law and its application so that we can answer this question easily. And understand the emissivity concept and emissive power.