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Home Minds On Refraction and Lenses Mission RL2 Light Speed and Refraction Help Help 9

Mission RL2 Light Speed and Refraction

The Question

A ray of light moving through air enters and passes through a series of parallel layers of different materials as shown below. Based on the direction of refraction at each of the boundaries, one can rank the relative speed of light in each material. The proper ranking of speed from fastest to slowest is _____.

Physics Rules

The Direction of Bending:
Refraction is the bending of the path of light as it passes across the boundary between two media. The direction of bending is dependent upon the relative speed at which light moves within the two media. The rules are:
  • When light passes from a medium in which it travels faster into a medium in which it travels slower, the light ray will refract towards the normal line.
  • When light passes from a medium in which it travels slower into a medium in which it travels faster, the light ray will refract away from the normal line.

Dig that Diagram

The diagram shows the path of light through several media which have been arranged in layers. Every time that a ray passes from one medium to another, it refracts - either toward or away from the normal. The direction which light bends provides information about the speed at which light travels within that medium (see Know the Law section).

Game Plan

Often times a good strategy is critical to success on a physics question. The following game plan should serve you well:
  1. Start with the first boundary - between layer A and layer B. Determine the direction which light refracts at this boundary. If it bends towards the normal, then light travels faster in medium A. Write down what you determine; you could quite easily forget it by the time you complete the next step.
  2. Next look at the boundary between layer B and layer C. Determine the direction which light refracts at this boundary. If it bends towards the normal, then light travels faster in medium B. Again, write down what you determine.
  3. Put the results of steps 1 and 2 together to determine the proper ordering of the layers according to speed.

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