WAEC Physics 2020 Paper

Concept:When light travels from glass into ethyl alcohol, Snell's law connects the refractive indices with the angles of incidence and refraction.Explanation:Let the angle of incidence in glass be $i = 30^{\circ}$.Let the angle of refraction in ethyl alcohol be $r$.Given refractive index of glass, $n_g = 1.5$.Given refractive index of ethyl alcohol, $n_e = 1.36$.Using Snell's law:$$n_g \sin i = n_e \sin r$$Substitute the values:$$1.5 \times \sin 30^{\circ} = 1.36 \times \sin r$$Since $\sin 30^{\circ} = 0.5$, we have:$$1.5 \times 0.5 = 1.36 \sin r$$$$0.75 = 1.36 \sin r$$$$\sin r = \frac{0.75}{1.36} = 0.5515$$Thus, the angle of refraction is:$$r = \sin^{-1}(0.5515) = 33.5^{\circ}$$Answer:The angle of refraction is $33.5^{\circ}$, which corresponds to option B.