Question

Assertion :Critical angle is minimum for violet colour. Reason: Because critical angle ${\theta }_c=si{n}^{-1}\left(\frac{1}{\mu }\right)$ and $\mu \propto \frac{1}{\lambda }$.

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

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

For total internal reflection to just take place, $\mu \sin {\theta }_c=1$

$⟹{\theta }_c=si{n}^{-1}\left(\frac{1}{\mu }\right)$

As a fact, the refractive index for a ray is inversely proportional to its

wavelength. This is the reason for deviation of red light to be least in a prism.

Thus ${\theta }_c$ decreases with $\lambda$.

Thus violet color has the least critical angle.