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.

How Much Does Light Bend?

• 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 of Light

• 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.

Refraction of Light - Lenses

• 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.

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