GEO - Introduction to Geometric Optics

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Geometric Optics

Introduction

When the Hubble Space Telescope was first launched in 1990 it promised to give astronomers the most impressive view of the cosmos ever achieved. When NASA scientists received the first images, however, they were a blurry mess. The primary mirror, responsible for focusing distant light onto one of the telescope's many cameras, was the wrong shape. Fortunately, the problem was solved when Hubble was fitted with corrective optics designed to eliminate the error in the primary mirror. You have had the human equivalent if you have ever been fitted for glasses or contact lenses. Our understanding of how light reacts when it encounters different materials led to your corrective glasses just as it did Hubble's corrective optics. This unit will help you to understand the basics of those optics.

Essential Questions

  1. What three things can happen when light strikes the boundary between two media?
  2. What is the difference between a real and virtual image?
  3. What is the law of reflection?
  4. What is Snell's Law?

Key Terms

  1. Medium - The material a wave travels through.
  2. Ray - A simplified model of light that represents light traveling in a straight line.
  3. Reflection - When a wave bounces off the boundary between two different mediums.
  4. Law of Reflection - States that the angle of incidence equals the angle of reflection when light strikes the boundary between two different media.
  5. Object - The source of the light interacting with a mirror or lens.
  6. Image -  The result of the light from the object interacting with a mirror or lens.
  7. Index of refraction - The ratio of the speed of light in a vacuum to the speed of light in a given medium.
  8. Refraction - The bending of a wave as it passes from one medium into another medium.
  9. Snell's Law - States the ratio of the angle of refraction to the angle of incidence is related to the ratio of the indices of refraction for the two media.
  10. Total internal reflection - The effect of light not being able to pass from a medium with a high index of refraction to one with a low index of refraction because of an angle of incidence greater than some critical angle.

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