Question

Inverse square law of luminance is valid for
(A). Isotropic point source
(B). Cylindrical source
(c). Search light
(D). All types of sources

Answer 1

Hint: This law describes the property of a light source. It is a specified physics law. This law describes the relation between the intensity of light and the distance between the light source and plane. This law is important in calculation of energy density of a light source also.

Complete step by step answer:
According to this law the intensity of light is inversely proportional to the square of distance between the plane and source of light.
Let us assume E be the intensity of the light and d is the distance between the source and plane. Therefore, according to this law
$E\propto {\displaystyle \frac{1}{d^2}}$
Remove the sign of expression and take a constant at the place of proportionality sign.
$E={\displaystyle \frac{I}{d^2}}$
Where I is the luminous intensity of the light at a given direction.
The expression of luminance can be expressed as follows:
${\displaystyle \frac{E_2}{E_1}}={\displaystyle \frac{d_1^2}{d_2^2}}$
This expression gives the relation between the two different sources of light placed at two different locations. This expression is valid for all types of sources of light. This law is applied when there is emission of light from a source to outside direction.
Therefore, inverse square law of Luminance is valid for all light sources

So, the correct answer is “Option D”.

Note:
First of all explain the definition of this law then establish a relationship between intensity of light and distance between the light source and plane and then explain the law’s validity for all types of light sources present in nature.