Question

Diagram alongside shows the paths of three rays A, B and C in water.

1. Copy the diagram and show the paths of rays when they strike the surface of water-air interface.
2. Does ray undergo refraction?
3. Name the phenomenon exhibited by C.
4. State the conditions necessary for phenomenon in С.

Answer 1

(a)

• Ray A strikes the surface along the normal, so it passes into air without bending.
• Ray B strikes the surface at 48°, which is the critical angle. It refracts at 90° and grazes along the water surface.
• Ray C strikes the surface at θ > 48°, which is more than the critical angle. It is totally reflected back into the water, with angle of reflection = θ.

(b) No, ray A does not bend. It strikes along the normal (angle of incidence = 0°), so it passes into air without deviation.

(c) Total internal reflection.

(d) Conditions for total internal reflection:

1. Light must travel from a denser medium (water) to a rarer medium (air).
2. The angle of incidence must be greater than the critical angle (48° for water).