Refraction

The term refraction is defined as the bending of light as it passes from one type of material into another. Because light travels at different speeds in the two materials, it changes its speed at the boundary of the two materials. If a beam of light hits this boundary at an angle, then light hitting the side first will be forced to slow down or speed up before light on the other side hits the new material. This causes the beam to bend, or refract, at the boundary.
Suppose we were to place a coin in a glass of water. The light bouncing off the coin underwater, for instance, would have to first travel through the water and then the air to reach an observer's eye. At the boundary, it gets refracted and reaches the observer's eye, thus appearing to be slightly raised.



In the pencil case, the pencil is placed at a specific angle and looks bent at the point where it touches the water, because light coming from the submerged portion of the pencil gets refracted as it crosses the water-air boundary.

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