# Activities

# The positions of the points on the screen are specified in meters - if you right-click on any point on the screen, the coordinates of that point will show up in yellow in the bottom left of medium 2 (the lower medium). The travel times for light over the various paths are given in nanoseconds - light is very fast!

1. When you first start the simulation, the three points are all along a vertical straight line. Click and drag the green point left and right to determine where the green point has to be to minimize the time it takes for light to travel from point 1 (red) to point 2 (purple). When the travel time is minimized, what do you notice about the values of n1 sin(θ1) and n2 sin(θ2)?
2. Now, click and drag point 1 (red) to a location in the upper left of medium 1, and move point 2 (purple) to a location in the lower right of medium 2. Once again, move the green point left and right to determine the path the light follows from point 1 to point 2 that minimizes the travel time. Try this in three different situations: (a) when the two media have the same index of refraction, (b) when medium 1 has a higher index of refraction than medium 2, and (c) when medium 1 has a lower index of refraction than medium 2. In all cases, when the travel time is minimized, what do you notice about the values of n1 sin(θ1) and n2 sin(θ2)?
3. What can you say about Snell's law, when the travel time is minimized?