Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: The phase difference of two light waves change if they travel through different media having same thickness, but different indices of refraction.
Reason R: The wavelengths of waves are different in different media.
In the light of the above statements, choose the most appropriate answer from the options given below

Assertion A: The phase difference of two light waves changes if they travel through different media having the same thickness but different indices of refraction.

This is correct. The optical path length is $$\mu t$$ where $$\mu$$ is the refractive index and $$t$$ is the thickness. Different $$\mu$$ values lead to different optical paths and hence a phase difference.

Reason R: The wavelengths of waves are different in different media.

This is correct. In a medium with refractive index $$\mu$$, the wavelength becomes $$\lambda/\mu$$.

R correctly explains A: since the wavelength changes in different media, the same physical thickness corresponds to different numbers of wavelengths, causing a phase difference between the two waves.

The correct answer is Both A and R are correct and R is the correct explanation of A.