Question

In the dispersion of white light from prism, the violet light is deviated more than the red light because:
A. Velocity of violet rays of light is more
B. Wavelength of violet rays of light is more
C. The frequency of violet rays of light is more
D. The refractive index of prism for violet rays of light is more

Answer 1

Hint: The wavelength and frequency of the deviated colors is different. They get deviated at different angles due to the difference in velocity in the prism. The red color deviates the least and the violet color deviates the most.

Formula used:
$\delta =(\mu -1)A$

Complete step by step answer:
Dispersion of white light is the phenomenon of splitting of white light into its constituent spectrum of colors, when it propagates through a glass prism. The figurative meaning of dispersion is distribution, and that’s what actually happens when light passes through glass dispersion; it gets distributed into its constituent colors – violet, indigo, blue, green, yellow, yellow, orange, and red. The white light gets splitted into its constituent colors at various frequencies and various angles.

Dispersion is a material property where the index of refraction is wavelength dependent. As the glass prism has positive dispersion, meaning the index of refraction will increase with the decrease in wavelength. As a result, shorter wavelengths undergo greater degree of refraction than the longer wavelengths.
In VIBGYOR pattern, red color has maximum wavelength, so it covers maximum distance inside the prism without deviation, but the violet color has minimum wavelength, so it gets spread inside the prism and deviates the most. We can say that Violet has the least velocity in the spectrum and it therefore undergoes maximum deviation while Red has the highest velocity in the spectrum and it therefore undergoes minimum deviation inside the glass prism.
Formula for angle of deviation inside glass prism:
$\delta =(\mu -1)A$
Where, $\mu $is the refractive index offered by glass prism and$A$is the angle of prism.
In conclusion, we can say that refractive index of glass is minimum for violet color, and therefore angle of deviation is maximum in case of Violet.
Hence, the correct option is D.

Note: Angle of deviation inside glass prism depends on: Angle of incidence, Angle of prism, and Wavelength of light. Students should not get confused between the wavelength of light and its frequency. Wavelength is the characteristic of its color while frequency is not. So when we talk about the angle of deviation for different colors, we will consider the wavelength of light and resulting refractive index. Frequency of light should not be considered here.