WAEC Physics 2020 Objective — Question 16
Question 16 of 50 from the West African Examinations Council (WAEC) Physics 2020 Objective paper, with the correct answer and a full explanation.
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A ray of light travelling from glass into ethyl alcohol is incident at the boundary at an angle of incidence 30 deg. Calculate the angle of refraction. [Refractive index of glass = 1.5; refractive index of ethyl alcohol = 1.36]
- A. 27.00 deg
- B. 33.50 degCorrect
- C. 51.70 deg
- D. 72.80 deg
Explanation
Using Snell's law: n = sin i / sin r, where n = n1 sin(theta1) = n2 sin(theta2), i.e. 1.5 sin30 = 1.36 sin r. So sin r = 1.5x0.5/1.36 = 0.75/1.36 = 0.55147, giving r = sin^-1(0.55147) = 33.46, approximately 33.50 deg.
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