Question

Three beams of red, yellow, and violet colours are passed through a prism, one by one under the same condition. When the prism is in the position of minimum deviation, the angles of refraction from the second surface are \( r_R \), \( r_Y \), and \( r_V \) respectively. Then,

• A. \( r_V>r_Y>r_R \)
• B. \( r_Y>r_R>r_V \)
• C. \( r_R>r_Y>r_V \)
• D. \( r_R = r_Y = r_V \)

Hint:

The angle of refraction for different colours of light passing through a prism varies with the refractive index, which is greater for shorter wavelengths (violet) and lower for longer wavelengths (red).

Answer 1

The Correct Option is C

Step 1: When white light passes through a prism, different wavelengths of light experience different amounts of deviation due to their different refractive indices in the prism material. Violet light, having the shortest wavelength, is refracted the most, and red light, with the longest wavelength, is refracted the least. Step 2: The angle of refraction in a prism depends on the refractive index, which in turn depends on the wavelength of light. The refractive index decreases as the wavelength increases. Step 3: Since the violet light has the highest refractive index, it will have the smallest angle of refraction \( r_V \). The red light, with the lowest refractive index, will have the largest angle of refraction \( r_R \). Yellow light lies in between, with an angle of refraction \( r_Y \). Step 4: Therefore, the order of angles of refraction is \( r_R>r_Y>r_V \). Conclusion: The correct option is (C) \( r_R>r_Y>r_V \).