If a light ray travels from denser to rarer medium. Which of the foll…

The correct answer is Option (2) → (B) and (D) only

In refraction the frequency is fixed by the source and does not change. The speed in a medium is \( v = c/n \), and the wavelength is \( \lambda = v/\nu \). A rarer medium has a smaller refractive index \( n \).

(A) Energy increases — Incorrect. The energy of a photon is \( E = h\nu \); the frequency does not change, so the energy does not change either.

(B) Frequency remain same — Correct. The frequency is a property of the source and stays the same in every medium.

(C) Phase changes by 90° — Incorrect. The refracted wave has no phase change; a phase change (of \( \pi \)) occurs only on reflection from a denser medium.

(D) Velocity increases — Correct. \( v = c/n \), and \( n \) is smaller in the rarer medium, so the speed increases.

(E) Wavelength decreases — Incorrect. \( \lambda = v/\nu \): the speed increases at the same frequency, so the wavelength increases.

NCERT (2026-27):
Refraction of a Plane Wave – “… The above equation implies that when a wave gets refracted into a denser medium (v₁ > v₂) the wavelength and the speed of propagation decrease but the frequency \( \nu \ (= v/\lambda) \) remains the same.”

Refraction at a Rarer Medium – “We now consider refraction of a plane wave at a rarer medium, i.e., v₂ > v₁.”