Rami Arieli: "The Laser Adventure" Snell's Law Applet

Snell's Law Applet

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This simulation can help you see what happens to a light beam, when it goes from one medium into another.
The light beam is refracted, according to Snell's Equation.
If the index of refraction of the medium where the beam comes from, is greater than the index of refraction of the other medium, there exists a critical angle.

For angles greater than the critical angle, the wave is reflected back, with the same angle, as the incident angle.

This phenomena is called: "Total Internal Reflection".
In this applet you can change the indices of refraction, and the incident angle as you like, and watch the result.


  1. Change the incidence angle, and check what happened to the refracted angle. Explain.

  2. Is the refracted angle bigger/Smaller, than the incidence angle?

  3. How does your answer agree with Snell's law?

  4. Since the angles are measured from the perpendicular to the boundary surface, does the refracted beam, approach the perpendicular, or further away from it?

Choose an index of refraction of the beam origin, higher than the index of refraction of the other medium.

  1. Change the incidence angle, and check what happened to the refractive angle?

  2. What happened when the value of the incidence angle, is higher than some specific value?

  3. The minimum value of the incidence angle that cause this is called "Critical Angle".
  4. What is the critical angle when a beam of light pass from water to air?

The table lists the index of refraction of some common materials:

Numerical Example:
The index of refraction of a fiber optic glass is 1.52.
What is the minimum angle at the entrance of a streight fiber, such that the light will stay within the fiber, and exit from the other end (as seen on the figure)?

Figure 1: Light confined to the optical fiber.