Refraction is the change in direction of a wave, caused by the change in the wave's speed. Examples of waves include sound waves and light waves. Refraction is seen most often when a wave passes from one medium to a different medium. Different types of medium include air and water. When a wave passes from one medium to another medium, the wave will change its speed and its direction. For example, when a light wave travels through air and then passes through water, the wave's speed will slow down and it will change direction.
An example of how refraction works is placing a straw in a cup of water, with part of the straw in the water. When looking at a certain angle, the straw appears to bend at the water's surface. This is because of the bending of light rays as they move between the air and the water.
A good and simple way to understand how light works is to think of it like a car. When the car hits the gravel surface (this is the medium) on an angle, the tire that hits it first will lock up, causing it to turn in that direction. Therefore, if light hits a medium on the right greater than its optical density, it will bend right.
When light refracts in a prism, it splits into colours of the rainbow.
Principles of refraction [change]
It recognizes that each point of an advancing wave front is in fact the center of a fresh disturbance and the source of a new train of waves; and that the advancing wave as a whole may be regarded as the sum of all the secondary waves arising from points in the medium already traversed.