Congratulations We have just discovered the earliest model of photo camera, Camera obscura'

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Congratulations!We have just discovered the
earliest model of photo camera, Camera obscura.
What are the drawbacks of the camera obscura?
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What kind of light is emitted by regular (not
self-luminous) objects?
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How do we see objects? Our vision involves
formation of images of different objects on the
retina of our eye.
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Reflection of Light

• A ray of light, the incident ray, travels in a
  medium
• When it encounters a boundary with a second
  medium, part of the incident ray is reflected
  back into the first medium

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The law of reflection
A single ray of light is incident upon a
reflecting surface at an angle q1 with the normal
to the surface.It is reflected at an angle q1
with the normal, such that q1 q1.The angle
of reflection is always equal to the angle of
incidence.
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The law of reflection
If the surface is flat and smooth, and the rays
in the incident beam of light are parallel to
each other (plane wave), they will all be
reflected at the same angle.This is the case of
specular reflection. If the surface is rough,
the law of reflection will still work for every
ray and every small element of surface. The law
of reflection will not work for the beam,
however, because of random orientation of
different surface elements. Different rays
constituting the beam will be reflected in random
directions, which is diffuse reflection.
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Specular reflectionan incident parallel beam
is reflected as a parallel beam
Diffuse reflectiona parallel beam is reflected
as bunch of diverging rays
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What type of reflection is more useful?
Well, it depends, what you actually want to get
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Which part of the figure below shows specular
reflection of light from the roadway?
With diffuse reflection you see the roadWith
specular reflection you see the lights of the car
reflected off the road.
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Mirrors are designed to give nice specular
reflection. Therefore the mirror surface is
invisible by itself.There are no point sources
of light on mirror surface. Therefore, looking
into a mirror you see reflections of objects, not
the mirror itself.
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Refraction of Light

• When a ray of light traveling through a
  transparent medium encounters a boundary leading
  into another transparent medium, part of the ray
  is reflected and part of the ray enters the
  second medium
• The ray that enters the second medium is bent at
  the boundary
• This bending of the ray is called refraction

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Refraction of Light.

• The incident ray, the reflected ray, the
  refracted ray, and the normal all lie in the same
  plane
• The angle of refraction, q2, depends on the
  properties of the two media and speeds of light
  in them, v1,2 c/n1,2

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Following (tracing) the Reflected and Refracted
Rays

• Ray ? is the incident ray
• Ray ? is the reflected ray
• Ray ? is refracted into the lucite
• Ray ? is internally reflected in the lucite
• Ray ? is refracted as it enters the air from the
  lucite

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• The angle of refraction depends upon the speeds
  of light in the two materials and the angle of
  incidence
• The path of the light through the refracting
  surface is reversible

• Refraction occurs because the speeds of light, v1
  and v2, are different in the two media
• The index of refraction, n, of a medium can be
  defined

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Snells law of refraction is written in a form
symmetric to the incident and refracted beams

• In terms of indices of refraction the law of
  refraction becomes
• Sine of angle of incidence (refraction) is
  inversely proportional to the index of
  refraction of the medium

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Media with high n, like diamond, are sometimes
called optically dense.

• For a vacuum, n 1
• For other media, n gt 1
• n is a unitless ratio, n c/v

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When light refracts into a material, where the
index of refraction is higher, the angle of
refraction is less than the angle of
incidence The ray bends toward the normal
When light refracts into a material, where the
index of refraction is lower, the angle of
refraction is greater than the angle of
incidence The ray bends away from the normal
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A material has an index of refraction that
increases continuously from top to bottom. Of
the three paths shown in the figure below, which
path will a light ray follow as it passes through
the material?
(b). When light goes from one material into one
having a higher index of refraction, it refracts
toward the normal line of the boundary between
the two materials. If, as the light travels
through the new material, the index of refraction
continues to increase, the light ray will refract
more and more toward the normal line.
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q1? 45
n1 1
q2? 5
n2 ?

• The angle q1 is too small to be real !