Waves
4 marks · EasyA ray of light passes from air into water at an angle of incidence of 35°. The angle of refraction inside the water is measured as 22°.
Calculate the refractive index of water. Show your working clearly.
Write down the equation relating angle of incidence and angle of refraction to refractive index.
Explain, in terms of wave speed, why refraction occurs when light passes from air into water.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) n = sin(35°)/sin(22°) = 0.574/0.375 ≈ 1.53
(b) Refractive index n = sin i / sin r
(c) Light changes speed when entering a new medium, which bends its path and causes refraction.
Show mark scheme and worked solution
Marking points
M1 (a) · 1 mark · Substitutes correctly into n = sin i / sin r. (follow-through)
A1 (a) · 1 mark · Correct answer for refractive index to 2 decimal places (1.53). (follow-through)
B1 (b) · 1 mark · States correct refractive index equation.
B1 (c) · 1 mark · Explains that refraction is due to change in speed as light enters a new medium.
Worked solution
a) n = sin i / sin r = sin 35° / sin 22° = 0.574 / 0.375 = 1.53
b) The equation is: refractive index n = sin i / sin r
c) Refraction occurs because light travels at different speeds in different media. The change in speed bends its path at the boundary.