In this video segment adapted from Shedding Light on Science, learn about the refraction of light. Observe how a straight straw placed in a bowl of water appears to bend where it enters the water. Learn about how the speed of light changes in different transparent materials and the direction of the light changes at the boundary of the materials. Fermat's principle of least time is explained through the analogy of a lifeguard on a beach trying to reach a swimmer in the water in the least amount of time.
This media asset was adapted from Shedding Light on Science.