Question

A point source of light is placed 4 m below the surface of water of refractive index 5/3. The minimum diameter of a disc which should be placed over the source on the surface of water to cut-off all light coming out of water is –

• A. 2 m
• B. 6 m
• C. 4 m
• D. 3 m

Answer 1

Answer: (B)

6 m

Answer 2

sin i = $\frac { 1 } { \mu }$ = $\frac { 3 } { 5 }$, tan i = $\frac { 3 } { 4 }$=

r = 3 m so diameter = 6 m