Question

Two coherent monochromatic light beams of intensities I and 4I are superimposed. The maximum and minimum possible intensities in the resulting beam are:

• A. 5 I and I
• B. 5 I and 3I
• C. 9 I and I
• D. 9 I and 3 I

Answer 1

Answer: (C)

9 I and I

Answer 2

Refraction at P.

⇒ $\operatorname { Sinr } _ { 1 } = \frac { 1 } { 2 }$

⇒ r₁ = 30⁰

Since r₂ = r₁

∴ r₂ = 30⁰

Refraction at Q Putting r₂= 30⁰ we obtain i₂ = 60⁰

Reflection at Q

$r _ { 2 } ^ { \prime } = r _ { 2 } = 30 ^ { \circ }$

∴ $\alpha = 180 ^ { \circ } - \left( r _ { 2 } ^ { \prime } + i _ { 2 } \right)$

= 180⁰- (30⁰+60⁰) = 90⁰