When a light ray passes through from air to water with a non-zero angle the ray will be
- A.bending towards the normal
- B.bending away from the normal
- C.propagating in straight line
- D.reflected towards the opposite direction
Correct answer
Explanation
The correct answer is A, bending towards the normal. Light slows down when it enters water from air, so a ray that strikes the surface at an angle bends towards the normal.
This bending is refraction. Water (refractive index about 1.33) is optically denser than air (about 1.00). By Snell's law, n₁ sin i = n₂ sin r, so when light goes into a denser medium the angle of refraction is smaller than the angle of incidence. Refraction is why a pool looks shallower than it is and a straight stick dipped in water looks bent at the surface. The question says "non-zero angle" because a ray falling along the normal passes straight through without bending.
B is wrong: a ray bends away from the normal when it goes from a denser medium to a rarer one, such as water to air. C is wrong: a ray travels straight only when it falls along the normal, at zero angle of incidence. D is wrong: a little light is reflected at the surface, but the ray that enters the water is refracted, not turned back.
Exam tip: Rarer to denser: towards the normal; denser to rarer: away from the normal; along the normal: no bending.
Practice Questions
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