Question

A point source of light is at a depth 'h' from the surface of a liquid of refractive index 1.25. A disc is so placed on the surface of liquid that it blocks all light
coming out from the surface. If minimum diameter of the disc is 8 m, depth of the source below the surface (h) is
Options
6 m
3 m
4.2 m
8 m
Clear Response​

Answer 1

Step-by-step explanation:

i don't know answer the question sorry

Answer 2

Answer:

Correct option is

A

(μ

2

−1)

1/2

2h

The figure shows incidence from water at a critical angle θ

c

for the limiting case.

Now, sinθ

c

=

μ

1

so that tanθ

c

=

(μ

2

−1)

1/2

1

From figure, tanθ

c

=

h

r

where r is the radius of the disc.

∴ Diameter of the disc 2r =2htanθ

c

,d=

(μ

2

−1)

1/2

2h