The light waves represented by the three rays shown in the diagram all have the same frequency. 4.7 wavelengths fit into layer 1, 3.2 wavelengths fit into layer 2, and 5.3 wavelengths fit into layer 3. Rank the layers according to the speeds of the waves, least to greatest.
A) 1, 2, 3
B) 2, 1, 3
C) 3, 1, 2
D) 3, 2, 1
E) 1, 3, 2

Question

The light waves represented by the three rays shown in the diagram all have the same frequency. 4.7 wavelengths fit into layer 1, 3.2 wavelengths fit into layer 2, and 5.3 wavelengths fit into layer 3. Rank the layers according to the speeds of the waves, least to greatest. 
A) 1, 2, 3 
B) 2, 1, 3 
C) 3, 1, 2 
D) 3, 2, 1 
E) 1, 3, 2

Quizplus · Accepted Answer

The speed of a wave is inversely proportional to the index of refraction of the material through which it is traveling. Layer 3 has the highest index of refraction, so it will have the slowest speed. Layer 2 has a lower index of refraction than Layer 3, but higher than Layer 1, so it will have an intermediate speed. Layer 1 has the lowest index of refraction, so it will have the fastest speed. Thus, the correct ranking is 3, 2, 1, which corresponds to choice D.

The Light Waves Represented by the Three Rays Shown in the Diagram