If a ray of light enters from a rarer medium to a denser medium at zero angle of incidence, it would
- (a)reflect back.
- (b)go straight.
- (c)turn towards right.
- (d)bend at 45°.
Correct — B, go straight. A ray striking a boundary at zero angle of incidence travels along the normal — straight into the surface. By Snell's law, if the angle of incidence is 0° then the angle of refraction is also 0°, so there is no bending: the ray continues straight into the denser medium (its speed drops, but its direction is unchanged). Bending occurs only when light meets the surface at an angle.
- (a)reflect back. — A ray along the normal passes into the denser medium; it is not reflected straight back — that would require mirror-like or total reflection, which does not happen when going from rarer to denser.
- (c)turn towards right. — There is no sideways turn at normal incidence — refraction bends a ray towards the normal only when it strikes at a non-zero angle.
- (d)bend at 45°. — No bending occurs at 0° incidence; a 45° bend would require a specific oblique angle and refractive index, not normal incidence.
Refraction is governed by Snell's law, n₁ sin i = n₂ sin r. When the angle of incidence i = 0 (the ray travels along the normal), sin i = 0 forces sin r = 0, so r = 0 and the ray goes straight through undeviated — even though its speed decreases in the denser medium. The amount of bending increases with the angle of incidence.
The intuitive trap is to assume that entering a denser medium always bends the ray. It bends only at oblique incidence; at perfectly normal (0°) incidence the ray passes straight through. Its speed still changes, but its direction does not.
- Snell's law: n₁ sin i = n₂ sin r; at i = 0°, r = 0° (no bending).
- At normal incidence a ray goes straight into the medium, undeviated.
- Its speed still decreases on entering the denser medium.
- Refraction bends light towards the normal (rarer → denser) only at oblique incidence.
- Assuming light always bends on entering a denser medium — it does not at 0° incidence.
- Confusing 'no bending' with 'no change' — the speed still changes.
Asked as the behaviour at normal incidence, or via Snell's-law bending direction for oblique rays.
No directly related past PYQ was found.
- practice — not a real PYQ
A ray of light passes from air into glass along the normal to the surface. It will
- (a)bend towards the normal
- (b)bend away from the normal
- (c)go straight without bending
- (d)be totally reflected
Answer(c) go straight without bending — at 0° incidence the angle of refraction is also 0°.
- practice — not a real PYQ
Light bends towards the normal when it travels from
- (a)denser to rarer medium
- (b)rarer to denser medium
- (c)one medium to the same medium
- (d)vacuum to vacuum
Answer(b) rarer to denser medium — for example air to glass, at oblique incidence.