NATURE OF LIGHT

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NATURE OF LIGHT
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CORPUSCULAR or PARTICLE THEORY
Sir Isaac Newton

• Light is made up of very fine particles, or
  corpuscles, that are emitted from sources at high
  temperatures. These particles travel in straight
  lines from the source to the observer at an
  enormous velocity.

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WAVE THEORY OF LIGHT
CHRISTIAN HUYGENS

• Light is a form of wave motion which starts from
  a vibrating body and is transmitted through space
  at high speed.

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THOMAS YOUNG

• Two light waves may meet in such a way that they
  may completely cancel each other. Instead of
  producing a brighter region, the two waves result
  in complete darkness.

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ELECTROMAGNETIC THEORY of LIGHT

• A changing electric field produces a magnetic
  field.

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VELOCITY of LIGHT (c)

• Velocity frequency x wavelength
• c f ? 3.0 x 10 8 m/s

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SOURCES of LIGHT

• 1. Natural sources

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• 2. Artificial sources
• Heating bodies to a very high temperature
• Passing an electrical discharge through a gas at
  a low pressure
• Combustion of chemical reaction

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RECTILINEAR PROPAGATION OF LIGHT

• If the light source is very tiny and concentrated
  in one place (a point source) only a sharp dark
  shadow (umbra) is formed.

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• If the source is broader light from the top of
  the source causes a lower shadow than that from
  the top. You therefore get partial shadow or
  penumbra (light shadow) as well as umbra.

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REFLECTION

• When a ray of light strikes any surface, a
  portion penetrates the surface and is either
  absorbed by the second medium or is transmitted
  if the second medium is transparent. The rest of
  the ray is reflected.

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LAWS of REFLECTION

• The angle of incidence is equal to the angle of
  reflection
• The incident ray, the normal ray and the
  reflected ray all lie in the same plane known as
  the plane of incidence.

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TYPES of REFLECTION

1. SPECULAR REFLECTION occurs when the reflecting
   surface is smooth and highly polished resulting
   to very sharp reflected rays
2. DIFFUSED REFLECTION occurs when the reflecting
   surface is more or less irregular resulting to
   scattered or diffused rays.

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For PLANE MIRRORS

1. Follow the Law of Reflection.
2. The image will be the same size as the object.
3. The distance of the image will be the same as the
   distance of the object.

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• 1. Sketch a ray diagram that shows how light will
  travel from the object to the eye by reflecting
  from the mirror in the given diagram. Show the
  position of the image.

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• 2. Measure how far the object is in front of the
  mirror. Draw a quick sketch of the image behind
  the mirror at the same distance

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• 3. Draw a light ray (a line) from the observers
  eye to an important part of the image (like the
  top). The light ray should be dashed when it is
  behind the mirror to show that the light ray
  isnt really there

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• 4. At the point where that light ray hit the
  mirror, bounce it back at the same angle (law of
  reflection) so that it hits the same spot on the
  original object.

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• 5. Draw another separate light ray that shows the
  path the light takes to get from the bottom of
  the object to the eye. You should get something
  that looks like this

Because the image isnt really a "thing" behind
the mirror (meaning that there are no true light
rays that are back there), we refer to it as a
virtual image.