Question

Which of the following is correct regarding a perfectly black body?

• A. Emissivity of perfectly black body is equal to 1
• B. Emissivity of perfectly black body is greater than 1
• C. Emissivity of perfectly black body lies between 0 and 1
• D. Emissivity of perfectly black body is equal to zero

Answer 1

The correct option is A Emissivity of perfectly black body is equal to 1

A good absorber is a good emitter. As perfectly black body absorbs all the radiation, it can also emit at all possible wavelengths. Therefore, emissivity of perfectly black body is equal to $1$.