WAEC Physics 2012 Theory — Question 3

Model answer

Since the reflected ray and refracted ray are perpendicular to each other (90° apart), and using the geometry of reflection/refraction, the angle of incidence θ must satisfy: the angle of refraction r = 90°−θ (since reflected angle = θ, and reflected+refracted+90° arrangement). Using Snell's law: n = sinθ/sin r = sinθ/sin(90°−θ) = sinθ/cosθ = tanθ. Thus, tanθ = 1.50, so θ = tan⁻¹1.50 = 56.3° (this angle is known as Brewster's angle).