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MCAT Physics Question — Snell’s Law

A beam of light is traveling through air (n = 1) when it passes through a transparent glass (n = 1.5) medium. Which of following is true concerning the angles θ and the velocity V?

physics snell's law question

A. θ1 > θ2 and V1 > V2

B. θ1 > θ2 and V1 < V2

C. θ1 < θ2 and V1 > V2

D. θ1 < θ2 and V1 < V2

Click for Explanation

This question tests the examinees understanding of Snell’s law of refraction, n1(sinθ 1) = n2(sinθ 2). The index of refraction (n) is the ratio of the speed of light to the speed of light through a specific medium. The index of refraction for air is 1, which means V1 is equal to the speed of light (3 x 108 m/s). The refraction index for glass is 1.5, which makes

V2 = 2 x 108 m/s. Therefore, B and D are eliminated.

To compare the angle of incidence (θ 1) to the angle of refraction (θ 2), use Snell’s law to determine the ratio. Since (sinθ 1)/(sinθ 2) = n2/n1, θ1 must be greater than θ2. Thus, A is the correct answer.

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