Black body MCQs
A body which absorbs all the heat radiations incident on its surface is called as perfectly black body. In practice the perfectly black body can be not be constructed. But the lamp black or the platinum black can be consider as a perfectly black body as they absorbs more than 98 % of the incident radiant energy.
The coefficient of absorption for black body is one i.e. a = 1, while t and r are zero. The emissive power of the perfectly black body at the given temperature is greater than any other ordinary body.
Ferry’s black body is one of the practical models. It consists of double walled hollow sphere with small opening called aperture. The outer side of sphere is nickel polished and inner wall is coated with lamp black. There is a conical projection exactly at diametrically opposite to the aperture. When the radiation is incident on the hole of this sphere, due to the conical projection the radiation that enters through hole suffers the multiple reflections. During each reflection more than 98 % of the incident radiant heat gets absorbed.
Q.1) For perfectly black body the values of coefficient of absorption, coefficient of transmission and coefficient of reflection respectively are..
a) 1, 0, 0
b) 0, 1, 0
c) 0, 0, 1
d) 1, 1, 1
Q.2) Which among the following materials are suitable for construction of black body?
a) nickel
b) platinum black
c) lamp black
d) both ‘b’ and ‘c’
Q.3) At given temperature, emissive power of perfectly black body is………that of ordinary body
a) same as
b) less than
c) more than
d) either less or more than
Q.4) The opening kept in hollow sphere for construction of Ferry’s black body is termed as….
a) hole
b) radiating path
a) aperture
d) exposure area
Q.5) The working of Ferry’s black body is depends upon the principle of…..
a) Reflection
b) Total internal reflection
c) Scattering
d) Diffraction
Q.6) The position of conical projection in Ferry’s black body is….
a) at any point of internal wall
b) just after aperture
c) diametrically opposite to aperture
d) none of these.
Q.7) Which among the following is correct for Perfectly black body?
a) It can transmit the entire radiations incident on it.
b) It can absorb the entire radiations incident on it.
c) The emissive power of black body is less than ordinary body.
d) All above statements are correct for black body.
Q.8) The gap between the doubled wall spheres in Ferry’s black body is……
a) evacuated
b) filled with absorptive material
c) filled with air
d) none of these.
Answers:
Q.1) a) 1, 0, 0
Q.2) d) both ‘b’ and ‘c’
Q.3) c) more than
Q.4) a) aperture
Q.5) b) Total internal reflection
Q.6) c) diametrically opposite to aperture
Q.7) b) It can absorb the entire radiations incident on it.
Q.8) a) evacuated
