Preparation for The Critical Angle and Fiber Optics Activity

In this activity, you will measure the critical angle for a plastic prism and then investigate the effects of total internal reflection for fiber optics.    The readings about these topics are found in the module on Reflection, Refraction, and Fiber Optics.

Preparatory Questions
Answer the following questions to the best of your ability before coming to class.  The in-class activity will give you an opportunity to check your predictions!

1. Snell's Law states that n₁ sin q₁ = n₂ sin q₂.  What does each symbol in the equation represent?
2. Consider the situation when q₂ = 90^o.  q₁ is then called the critical angle q_c.  For any angles q₁ > q_c, total internal reflection occurs.   Which index of refraction, n₁ or n₂ must be larger for this to occur?  Explain.
3. In the experiment you will perform, the two media will be plastic and air.   You will measure the index of refraction for the plastic.  Do you expect to see total internal reflection when the light travels into the plastic from the air, when it travels into the air from the plastic, or both?   Explain.
4. What would the critical angle for the plastic be if its index were 1.54?
5. If you were using total internal reflection to trap light inside a fiber, would the core (inner layer) index have to be less than or greater than the cladding (outer layer) index of refraction?  Explain.