Refraction of Light

Introduction

Refraction: the bending of light (it also happens with sound waves, water waves and other waves) as it passes from one transparent substance into another.
This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows.
Even our eyes depend upon this bending of light.
Without refraction, we would not be able to focus light onto our retina.
Change of speed causes change of direction.
Light refracts whenever it travels at an angle into a substance with a different refractive index (optical density).
This change of direction is caused by a change in speed of light.

When light travels from air into water, it slows down, causing it to change direction slightly.
- This change of direction is called refraction.
When light enters a more dense substance (higher refractive index), it ‘bends’ more towards the normal line.
Extent of refraction depends on refractive indexes, n.

Refraction can create a spectrum.
Isaac Newton performed his experiment using a triangular block of glass called a prism.
- He used sunlight shining in through his window to create a spectrum of colors on the opposite side of his room.
- This experiment showed that white light is actually made of all the colors of the rainbow.
- These seven colors are remembered by the acronym ROY G BIV – red, orange, yellow, green, blue, indigo and violet.
When white light shines through a prism, each color refracts at a slightly different angle.
- Violet light refracts slightly more than red light.
- A prism can be used to show the seven colors of the spectrum that make up white light.

Biconvex lens: thicker at the middle than it is at the edges.
- This is the kind of lens used for a magnifying glass.
- Parallel rays of light can be focused in to a focal point.
- A biconvex lens is called a converging lens.
- Each light ray entering a converging (convex) lens refracts inwards as it enters the lens and inwards again as it leaves.
- These refractions cause parallel light rays to spread out, travelling directly away from an imaginary focal point.
Biconcave lens: curves are thinner at the middle than it is at the edges.
- Light rays refract outwards (spread apart) as they enter the lens and again as they leave.
- Each light ray entering a diverging (concave) lens refracts outwards as it enters the lens and outwards again as it leaves.
- These refractions cause parallel light rays to spread out, travelling directly away from an imaginary focal point.