When a ray of light enters a glass slab, then

[amp_mcq option1=”only the frequency changes” option2=”frequency and velocity change” option3=”frequency does not change” option4=”frequency and wavelength change” correct=”option3″]

This question was previously asked in

UPSC NDA-2 – 2016

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When light passes from one medium to another (like air to glass), its speed changes, and its wavelength changes. However, the frequency of the light, which is determined by the source, remains constant.

The speed of light ($v$), frequency ($f$), and wavelength ($\lambda$) are related by the equation $v = f\lambda$. When light enters a denser medium, its speed decreases. Since frequency ($f$) is constant, the wavelength ($\lambda = v/f$) must decrease proportionally.

The change in speed and wavelength leads to the phenomenon of refraction, where the light ray bends at the interface between the two media (unless it enters perpendicularly). The energy of the light is also proportional to its frequency (E = hf), so frequency remaining constant means the energy of each photon is conserved.

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