Description
This is a simulation based on a problem on the publicly released 2015 AP Physics 2 exam. I used the actual indices of refraction given in the problem, and made the simulation to the same scale as used in the problem. The simulation shows why you see two dots at the bottom of the glass when the original angle of incidence is small enough. It also illustrates why the second dot gets brighter when the critical angle of incidence is reached at the liquid-air interface. The simulation also shows that the part of the problem about why the second dot disappears is misleading. The problem states that the second dot disappears due to total internal reflection, but you can see in the simulation that the second dot would actually disappear due to its ray not hitting the bottom of the glass container long before the critical angle for the glass-liquid interface is reached.