Electromagnetic Waves

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Electromagnetic Waves

• Part II

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So far

• We have discussed
• The nature of EM waves
• Some of the properties of EM waves.
• Now we will discuss
• EM waves and optics
• Mirrors
• Lenses
• Applications

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Reflection Refraction
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Reflection
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Light Reflection

• Angles of incidence measured from the NORMAL to
  the mirror.
• For reflection The angle of incidence equals
  the angle of reflection.

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Principle of Least Time
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The light rays appear to come from behind the
mirror.
An image is virtual if the light rays from a
point on the object are directed as if they
diverged from a point on the image, even though
the rays do not actually pass through the image
point.
Your eye focuses the diverging rays reflected by
the mirror.
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Mirror, Mirror, on the wall, how big do you have
to be to see it all? The strange world of images.
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The speed of light

• Light travels at a speed c in a vacuum.
• In an actual material, it travels a bit slower,
  at a velocity of v.
• The speed of light depends on the material
  through which it is traveling.
• DEFINITION INDEX OF REFRACTION (or refractive
  index)

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Index of Refraction
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Notice
For two materials
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Huygens Principle
Each point on a wavefront acts as a secondary
source of spherical waves that progress from
the source at the speed of light (whatever it may
be). A spherical wave with very large
radius, behaves as a plane wave.
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.
Not there yet!
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The Wave Nature of Light

• The law of refraction is explained by Huygens
  Principle

The little wavelets move slower in medium 2 than
in medium 1. Doing the tangent shows how the
wave fronts bend.
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Some Geometry
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The Wave Nature of Light
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Snells Law of Refraction
Law of Reflection
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Another ViewOf Reflection(Huygens)
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Both Together
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At the critical angle and beyond, only reflection
is possible.
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Total Reflection Optical Fiber
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A cross section of a submarine communications
cable.1 - Polyethylene2 - Mylar tape3 -
Stranded steel wires4 - Aluminium water
barrier5 - Polycarbonate6 - Copper or aluminum
tube7 - Petroleum jelly8 - Optical fibers
Lengths of 100 KM are possible before
amplification is necessary. Thousands of
conversations can be carried on a single fiber.
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Polarization
Waves on a string.
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dichroism
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1 of opposite polarization
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Mirage
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