The Black Body and Kirchoff's Law - 1 - MCQs with Answers

The Black Body and Kirchoff's Law – 1 – MCQs with Answers

1. What is the black body or an ideal radiator?

a. the body which transmits all the radiations incident upon it
b. the body which absorbs all the radiations incident upon it
c. the body which reflects all the radiations incident upon it
d. none of the above

ANSWER: b. the body which absorbs all the radiations incident upon it

2. As a radiator, the black body emits the maximum possible thermal radiation

a. at a constant single wavelength
b. at the maximum wavelength
c. at all wavelengths
d. none of the above

3. Which of the following sentences are correct for black body

(1) The black body is a hypothetical body
(2) The black body is a real body
(3) The black body is used as a standard of perfection against which the radiation characteristics of other bodies are compared

a. sentences (1) and (2)
b. sentences (1) and (3)
c. sentences (2) and (3)
d. all the sentences (1), (2) and (3)

ANSWER: b. sentences (1) and (3)

4. What is the relation between emissive power of a real body (E) and emissive power of black body (Eb) when both are at same temperature?

a. Eb / E = 1
b. Eb / E = α
c. E / Eb = 1
d. E / Eb = α

Where,
α =absorptivity

ANSWER: d. E / Eb = α

5. The emissivity (ε) can be defined as the ratio of

a. emissive power of real body to the emissive power of black body
b. emissive power of black body to the emissive power of real body
c. reflectivity of real body to emissive power of black body
d. reflectivity of black body to emissive power of real body

ANSWER: a. emissive power of real body to the emissive power of black body