General operation: Tap/click anywhere in the area labeled "Medium 1" to change the position of the laser. The button on the laser turns the laser on and off. Use the menus to select the material for each medium, or use the sliders to set a custom value for each index of refraction.
Quiz mode: When you press the "Quiz" button, "Medium 2" is set to a random index of refraction. Enter values for the angle of incidence (θi), the angle of refraction (θr), and the index of refraction, which you will have to compute using Snell's law. A calculator and protractor are provided for this purpose. When you press "Show Results", you will see how close your measurements and calculations are to the actual values.
Snell's Law: Snell's law is shown below in two forms.