Question

The critical angle for a ray of light passing from glass to water is minimum for

• A. \( \) red colour
• B. \( \) blue colour
• C. \( \) yellow colour
• D. \( \) violet colour

Hint:

The critical angle for different colours of light depends on their wavelength. Shorter wavelengths (such as violet) result in smaller critical angles.

Answer 1

The Correct Option is D

Step 1: The critical angle \( \theta_c \) is given by the formula: \[ \sin \theta_c = \frac{n_2}{n_1} \] where \( n_1 \) and \( n_2 \) are the refractive indices of the two media. Step 2: The refractive index of a medium depends on the wavelength of light. Violet light has a shorter wavelength than red light and thus a higher refractive index. As a result, the critical angle for violet light is smaller than for red light. Step 3: Since the critical angle is inversely proportional to the refractive index, the critical angle is minimum for violet light (the shortest wavelength). Conclusion: The critical angle for a ray of light passing from glass to water is minimum for violet colour.