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Home Minds On Refraction and Lenses Mission RL3 Optical Density, n, and Refraction Help Help 9

Mission RL3 Optical Density, n, 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 index of refraction of each material. The proper ranking of the n values from largest to smallest 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 refraction 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.

Physics Rules

Optical Density, Speed of Light and Index of Refraction:
The speed at which light travels through a medium is dependent upon the optical density of that medium. Light travels fastest in media that are least optically dense. The index of refraction value provides a relative measure of the optical density of a material. The higher the index of refraction value, the more optically dense a material is and the slower that light will travel in that material.

Game Plan

Often times a good strategy (and some good thinking) 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 that light refracts at this boundary. If it bends away from the normal, then light travels slowest 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 that light refracts at this boundary. If it bends away from the normal, then light travels slowest 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.
  4. The question asks you to order the layers according to the index of refraction value. The greater the speed, the smaller the index of refraction value.

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