Question

A small source of light is 4 m below the surface of water of refractive index 5/3. In order to cut off all the light,

Answer 1

Q) small source of light is 4 m below the surface of water of refractive index 5/3. In order to cut off all the light, corning out of water surface, minimum diameter of the disc placed on the surface of water is

(a) 6 m

(b) ∞

(c) 3 m

(d) 4 m.

ANS)n order to cut of fall the light coming out of water surface, angle C should be equal to critical angle.

sinc=1/5/3=3/5

now tan c=3/4

tanc =r/h

r=h tanc= 4x 3/4= 3m

diameter=2r=6