Question

(a) Define absolute refractive index of a medium. (b) The radius of curvature of concave mirror is 50cm. Where should an object be placed from the mirror so as form its image at infinity? Justify your answer.

Answer 1

a: absolute refractive index = c/v
I.e.speed of light in air with respect to speed of light in second transparent medium.
b: f = 50/2
f = 25 cm
so,1/f=1/u +1 v
1/25 = 1/u + 1/infinity
u = 25 cm
so,the object distance is 25 cm

Answer 2

(a)  The refractive index of a medium with respect to vacuum is called Absolute refractive index.

(b) Given:

         Radius of curvature, R= 50 cm

we know that,

           f = R/2

             =50/2 = 25 cm

then,

      1/f =  1/v + 1/u

     1/25 = 1/∞ + 1/u

     Object distance, U = 25 cm