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  4. 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.

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Q. 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.

Ray Optics and Optical Instruments

Solution:

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.