Question

Light is incident normally on face AB of a prism as shown in figure. A liquid of refractive index m is placed on face AC of the prism. The prism is made of glass of refractive index 3/2. The limits of m for which total internal reflection takes place on face AC is –

• A. m> $\frac { \sqrt { 3 } } { 2 }$
• B. m<$\frac { 3 \sqrt { 3 } } { 4 }$
• C. m> $\sqrt { 3 }$
• D. m< $\frac { \sqrt { 3 } } { 2 }$

Answer 1

Answer: (B)

m<$\frac { 3 \sqrt { 3 } } { 4 }$

Answer 2

Critical angle between glass & liquid face is

sin q_c = $\frac { \mu } { 3 / 2 }$ = $\frac { 2 \mu } { 3 }$

for T/R to take place i > q_c

sin 60⁰ > $\frac { 2 \mu } { 3 }$Ž m < $\frac { 3 \sqrt { 3 } } { 4 }$