Question

Assertion A white light on passing through prism splits into its component colour such that the red light emerges nearest to the base of the prism.
Reason Wavelength of red light is more than other component colours and hence, red light deviates least.

• A. Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
• B. Both Assertion and Reason are correct but Reason is not the correct explanation of Assertion.
• C. Assertion is correct but Reason is incorrect.
• D. Assertion is incorrect but Reason is correct.

Answer 1

Answer: (D)

Dispersion takes place because the refractive index of medium for different wavelengths (colours) is different. The refractive index is inversely proportion to $\lambda$ by Cauchy's expression as
$\mu (\lambda )=r+\frac{b}{{\lambda }^2}+\frac{c}{{\lambda }^4}$
Hence, deviation $(D)=(\mu -1)A$
Since ${\lambda }_{\text{red }}$ is more than other colours wavelength.
So, deviation is least for red and have it appears farthest from the base of the prism.