When light travels from one transparent medium to another, it changes speed. This change in speed also makes the light change direction. This is why a paint brush in a glass of water seems broken at the water's surface.

Source: : Refraction Verre, No-w-ay, Wikimedia commons

The path the light takes is determined by Snell's Law. Move your mouse over the formula to see more information.

Play the following video to watch a group of students investigating refraction using a beam of laser light moving through a lens made of water in a plastic dish, and then answer the questions.

How did the angle of the laser light in the water compare to the angle in the air?

Interactive popup. Assistance may be required.

Check Your Answer

The angle in the air was larger than the angle in the water.

What happened when the angle in the water hit 49°?

Interactive popup. Assistance may be required.

Check Your Answer

This was what the students found for the critical angle. The light reflected back into the water.