Question

On passing a ray of white light through a prism, the colour which has minimum deviation is:

• A. green
• B. yellow
• C. red
• D. violet

Hint:

In a prism, red light deviates the least, while violet light deviates the most due to their respective wavelengths.

Answer 1

The Correct Option is C

When white light passes through a prism, it undergoes a process known as dispersion. Dispersion occurs because different colors of light have different wavelengths and, consequently, they interact with the prism in different ways. The key principle is that the amount of deviation or bending of light depends on its wavelength. \smallskip 1.
Wavelength and Deviation:

The prism bends light because of the change in speed as light enters and exits the prism. This bending is governed by the refractive index of the material of the prism. The refractive index is wavelength-dependent, meaning it varies for different colors of light.
The refractive index is higher for shorter wavelengths (violet), meaning violet light bends more than longer wavelengths (red). Conversely, red light, having the longest wavelength, is least affected by the prism’s refraction.
\smallskip 2.
Deviations for Different Colors:

The amount of deviation of light through the prism is related to the wavelength of the light. Red light, with its longer wavelength, experiences the least deviation because it is refracted less.
Violet light, on the other hand, with its shorter wavelength, is refracted more and therefore deviates the most.
\smallskip 3.
Minimum Deviation for Red Light:

The color red, being the least refracted, experiences the smallest angular deviation from its original path after passing through the prism. This is why red light is said to have the minimum deviation, as it deviates the least compared to all other colors.
\smallskip In conclusion, when white light passes through a prism, the different colors are separated, with red light experiencing the least deviation and violet light experiencing the most. Thus, red light has the minimum deviation, and this phenomenon is a consequence of the varying refractive indices for different wavelengths of light.