Why do lenses refract light

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Test sensitivity - specificity calculator. 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. This flip may seem trivial, but this behavior can lead to interesting results.

For one thing, this property can be used to make cloaking devices. More to our point, though: a flat, uniform piece of meta-material can act just like a convex lens and is able to focus light.

We can show this by tracing the light rays through a flat piece of meta-material, being careful to flip the rays across the normal as happens in real life. The result is shown below. Meta-materials do not occur in nature and they are hard to fabricate, so there are not yet many commercial applications using flat plates of meta-materials to focus light.

Topics: Fresnel lens , GRIN , bending , lens , light , metamaterial , optics , reflection , refraction. Refraction of light means that light bends when it enters a material with a different refractive index. In these diagrams white represents air, blue represents glass, the gray dotted line is the normal direction, and the black line is the path of the light.

Light bends towards the normal when entering higher-index standard materials left diagram and away from the normal when exiting higher-index standard materials right diagram.

Public Domain Image, source: Christopher S. Standard concave lenses use refraction to spread out light. Standard convex lenses use refraction to focus light. A standard flat plate does not change much at all. A Fresnel lens is conceptually constructed by starting with a convex lens, removing all useless material while keeping the entrance surface normal to the entering light, and then aligning the remaining bits in a plane.

A Fresnel lens is essentially a flat although rough object that focuses light like a convex lens. A graded-index lens is a flat object that focuses light by changing the refractive index of the material as you go from the lens' center to its edge. As you can see, when a ray passes through the center of the lens C it is not refracted. Back to chapter How do lenses refract light?