Why is light refracted

This causes them to change direction, an effect called refraction. At the boundary between two transparent substances:. The diagram shows how this works for light passing into, and then out of, a glass block. Isaac Newton performed a famous experiment using a triangular block of glass called a prism.

He used sunlight shining in through his window to create a spectrum of colours on the opposite side of his room. This experiment showed that white light is actually made of all the colours of the rainbow. Newton showed that each of these colours cannot be turned into other colours.

He also showed that they can be recombined to make white light again. The explanation for the colours separating out is that the light is made of waves. Red light has a longer wavelength than violet light. The refractive index for red light in glass is slightly different than for violet light. Violet light slows down even more than red light, so it is refracted at a slightly greater angle.

The refractive index of red light in glass is 1. The refractive index of violet light is 1. This slight difference is enough for the shorter wavelengths of light to be refracted more.

A rainbow is caused because each colour refracts at slightly different angles as it enters, reflects off the inside and then leaves each tiny drop of rain. A rainbow is easy to create using a spray bottle and the sunshine. The centre of the circle of the rainbow will always be the shadow of your head on the ground. The secondary rainbow that can sometimes be seen is caused by each ray of light reflecting twice on the inside of each droplet before it leaves.

This second reflection causes the colours on the secondary rainbow to be reversed. The second condition is also reasonable. If the students approach the masking tape in a direction that is perpendicular to it, then each student will reach the tape at the exact same time. Recall that the line of student changed their direction because they had reached the masking tape at different times. The first student reached the tape, slowed down, and observed the rest of the students marching ahead at the original speed.

The change in direction of the line of students only occurs at the boundary when the students change speed and approach at an angle. The Marching Soldiers analogy provides an excellent analogy to understanding the cause of light refraction. The line of students approaching the masking tape are analogous to a wavefront of light. The masking tape is analogous to a boundary between two media.

The change in speed that occurred for the line of students would also occur for a wave of light. And like the marching students, a light wave will not undergo refraction if it approaches the boundary in a direction that is perpendicular to it. The same two conditions that are necessary for bending the path of the line of students are also necessary for bending the direction of a light ray. Light refracts at a boundary because of a change in speed.

There is a distinct cause-effect relationship. The change in speed is the cause and the change in direction refraction is the effect. Physics Tutorial. My Cart Subscription Selection. Student Extras. Flickr Physics Photo.