Question

When light ray undergoes two internal reflection inside a raindrop, which of the rainbow is formed?

• A. Primary rainbow
• B. Secondary rainbow
• C. Both (1) and (2)
• D. Can’t say

Answer 1

Answer: (C)

Both (1) and (2)

Answer 2

Intensity α (Amplitude)²

⇒ I α A²

When two waves (beams) of amplitude A₁ and A₂ superimpose, at maxima and minima, the amplitude of the resulting wave are (A₁ + A₂) and (A₁ - A₂) respectively. If the maximum and minimum possible intensities are I_max and I_min respectively, then

I_max α (A₁ +A₂ ) ²

and I_min α (A₁ – A₂ ) ²

⇒ $\frac { I _ { \text {max } } } { I _ { \text {min } } } = \left( \frac { A _ { 1 } + A _ { 2 } } { A _ { 1 } - A _ { 2 } } \right) ^ { 2 } = \left\{ \frac { \frac { A _ { 1 } } { A _ { 2 } } + 1 } { \frac { A _ { 1 } } { A _ { 2 } } - 1 } \right\} ^ { 2 }$

where $\frac { A _ { 1 } } { A _ { 2 } } = \frac { \sqrt { l } } { \sqrt { 4 I } } = \frac { 1 } { 2 }$

⇒

⇒ I_max = 9I, I_min = I