Light Refraction Tank Analogy

As it enters the sandy section,

• the tank will turn right (from the drivers view) to some degree because the speed of tread A will slow down while tread B continues to turn at its normal speed.
• This will turn the tank as shown in the schematic.
• The tank turns towards a vertical perpendicular line drawn where the tank enters the surface (we can see it turns towards the Normal).

When tread B enters the sandy section,

• it will also slow down to the speed of tread A.
• The tank will now continue on a straight line until it begins to cross the sandy boundary on the other side.
• It’s speed is reduced now.

As the tank exits the sandy section into the smooth road again,

• tread A speeds up before tread B does, so the tank will turn to the left (from the driver’s point of view).
• This time it turns “away from the Normal” line drawn where the tank exits.
• When both treads are out of the sand completely the tank assume a straight path again and
• it resumes the faster speed it had before entering the sandy section.

This “macro” analogy gives us an intuitive feel for why light bends when it enters a refractive medium and the direction in which it bends:

Picture_Light Travelling through Refractive Medium

• Light will slow down when it enters from air into a higher refracting medium.
• At the boundary of the medium it will refract “towards the Normal” and will begin to slow down to a new, slower speed in the medium(due to electromagnetic wave interference caused by medium “vibrating” electrons).
• When the light enters the air from the refractive medium, it will turn “away from the Normal” and it will resume the same speed in air it had before entering the medium.