Identify the correct statements among the following in the context of the phenomenon of refraction of light.
A. Light rays do not deviate from their path while travelling from one medium to another when they are incident normally at the interface between the two media.
B. If light ray bends away from normal after refraction then second medium is optically denser. If the light ray bends towards normal, then second medium is optically rarer.
C. The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for a given pair of media.
D. The velocity and frequency of the incident ray change when it travels from one medium to another after refraction.
E. The incident ray, the refracted ray and the normal to the interface of two transparent media, at the point of incidence, all lie in the same plane.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, C and E only
Refraction obeys Snell’s law, and the frequency does not change.
(A) Light rays do not deviate from their path while travelling from one medium to another when they are incident normally at the interface between the two media. — Correct. For \( i = 0 \), \( \sin r = 0 \), so \( r = 0 \) and the ray goes straight on.
(B) If light ray bends away from normal after refraction then second medium is optically denser. If the light ray bends towards normal, then second medium is optically rarer. — Incorrect. It is the other way round: a ray bends towards the normal on entering a denser medium.
(C) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant for a given pair of media. — Correct. This is Snell’s law.
(D) The velocity and frequency of the incident ray change when it travels from one medium to another after refraction. — Incorrect. The speed changes, but the frequency stays the same.
(E) The incident ray, the refracted ray and the normal to the interface of two transparent media, at the point of incidence, all lie in the same plane. — Correct. This is the first law of refraction.
NCERT (2026-27):
Refraction – “… Snell experimentally obtained the following laws of refraction: (i) The incident ray, the refracted ray and the normal to the interface at the point of incidence, all lie in the same plane. (ii) The ratio of the sine of the angle of incidence to the sine of angle of refraction is constant.”
Refraction – “… From Eq. (9.10), if \( n_{21} \gt 1 \), \( r \lt i \), i.e., the refracted ray bends towards the normal. In such a case medium 2 is said to be optically denser (or denser, in short) than medium 1.”
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/λ) remains the same.”