REFLECTION

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REFLECTION
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REFLECTION

• Definition
• If a ray of light hit the boundary and returns
  back to the same medium, the phenomenon is called
  reflection

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REFLECTION
the ray of light approaching the surface is
incident ray (I). ray of light which leaves the
mirror is reflected ray ( R ) The normal line
divides the angle between the incident ray and
the reflected ray into two equal angles
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Angle of incidence Angle of reflection

• Angle of incidence
• The angle between the incident ray and the normal
  is known as the angle of incidence, and is
  denoted by ?i
• Angle of reflection
• The angle between the reflected ray and the
  normal is known as the angle of reflection and is
  represented by ?r

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Laws of Reflection

• When a ray of light reflects off a surface
• 1. The angle of incidence ?i is be equal to the
  angle of reflection ?r.
• ?i ?r
• 2.The incident ray, the reflected ray and the
  normal all lie in the same plane.

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Types of reflection

• 1. Specular Reflection
• 2. Diffuse Reflection
• 3. Retro reflection

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1.Specular Reflection

• If the reflection takes place from a smooth
  surface then all the reflected rays will be
  parallel to each other.

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2.Diffuse Reflection

• In such reflections different rays after
  reflection travel in different directions.
• However, the reflection from a rough surface is
  known as diffuse reflection.
• the laws of reflection is obeyed in such cases
  too.

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3. Retro reflection

• If the ray of light after reflection returns back
  to the same path as the incident ray, that
  reflection is called retro reflection.
• Retro reflection occurs when the incident rays
  fall normally to the reflecting surface.
• In such case, ?i ?r 0o

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Refraction of Light

• The incident ray, the reflected ray, the
  refracted ray, and the normal all lie on the same
  plane
• The angle of refraction, ?2, depends on the
  properties of the medium

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Refraction of Light

• The ray that enters the transparent medium is
  bent at the boundary
• This bending of the ray is called refraction

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Refraction Details.

• Light may refract into a more denser material
• 1. its speed is lower
• 2. The angle of refraction is less than the angle
  of incidence
• 3.The ray bends toward the normal

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Refraction Details, 2

• Light may refract into a less denser material
• 1. speed is higher
• 2. The angle of refraction is greater than the
  angle of incidence
• 3. The ray bends away from the normal

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The Index of Refraction (n)

• When light passes from one medium to another, it
  is refracted because the speed of light is
  different in the two media
• The index of refraction, n, of a medium can be
  defined

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More definition
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Laws of Refraction

• 1.The incident ray, the refracted ray, and the
  normal all lie in the same plane.
• 2. The ratio of the sine of the angle of
  incidence to the sine of angle of refraction is
  constant for any two given media. This is known
  as Snells Law

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Snell's Law

• Snell's Law may be written as

1n2 and is called as the refractive index of
medium 2
with respect to the medium 1.
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refractive index..

• The value of the refractive index (n) depends on
• i) the nature of the pair of media 1 and 2
• ii) the wavelength (color) of light.
• For Ex nv gt nr
• The refractive index of a medium is greater
  for violet light (shorter wavelength) than that
  for the red light (longer wavelength).

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refractive index..

• If a ray of light passes from medium-1 (absolute
  refractive index n1) to medium-2 (absolute
  refractive index n2), we may write

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refractive index with speed .

• refractive index of medium 2 with respect to
  medium1, in terms of velocity of light is given
  by

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refractive index , frequency

• When the light travels from one medium to the
  other medium, its frequency does not change.
• Therefore, because the relation v f ? must be
  valid in both the media, and
• since f1 f2, it is clear that

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refractive index with frequency and wavelength
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Dispersion
If a beam of white light is incident on the prism
then the rays coming out of the prism will
spread . This is called Dispersion. in series
of colors called the visible spectrum. The
spreading of light into its constituent colors
is observed because the angles of deviations for
different colors have different values. The
deviation is maximum for violet color and least
for the red.
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Angle of deviation, d

• The amount the ray is bent away from its original
  direction is called the angle of deviation, d
• Since all the colors have different angles of
  deviation, they will spread out into a spectrum
• Violet deviates the most
• Red deviates the least

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Total Internal Reflection
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Critical Angle

• A particular angle of incidence , the angle of
  refraction of 90
• This angle of incidence is called the critical
  angle

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Total Internal Reflection

• Definition-
• If the angle of incidence is larger than the
  critical angle, then the angle of refraction
  would become gt 90O and the ray will return back
  to the previous medium , this , phenomenon is
  called total internal reflection.

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Refractive Index and critical angle
If the second medium is air then n2 1 and
then taking n1 n, we get
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Conditions for the Total Internal Reflection

• 1.The ray should travel from denser to rarer
  medium.
• 2.The angle of incidence should be greater then
  the critical angle.

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Fiber Optics

• This is an important and interesting
• application of total internal reflection.
• 2. Solid glass or transparent plastic pipes are
  used to send the light signals from one to other
  place.
• 3. A bundle of thin fibers are used to construct
  an optical line

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Fiber Optics
Optical fibers, as shown , consist of transparent
core surrounded by cladding of lower refractive
index than the core. There is a cone of certain
angle at the entrance of the fiber. The light
entering within this cone to the fiber will be
transmitted. This cone is called the acceptance
cone. The acceptance cone will be larger if this
critical angle of the core-cladding surface is
smaller. This is therefore achieved by taking
suitable combination of the core and cladding.
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PROBLEM1.1

• The two mirrors in Figure P22.6 meet at a right
  angle. The beam of light in the vertical plane P
  strikes mirror 1 as shown. (a) Determine the
  distance the reflected light beam travels before
  striking mirror 2. (b) In what direction does the
  light beam travel after being reflected from
  mirror 2?

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PROBLEM1.1
(b)
(a) From geometry,
, so
, or parallel to the incident ray
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PROBLEM1.2

• An underwater scuba diver sees the Sun at an
  apparent angle of 45.0 from the vertical. What
  is the actual direction of the Sun?

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PROBLEM1.2

• 1.2

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PROBLEM1.3

• A laser beam is incident at an angle of 30.0 to
  the vertical onto a solution of corn syrup in
  water. If the beam is refracted to 19.24 to the
  vertical, (a) what is the index of refraction of
  the syrup solution? Suppose the light is red,
  with vacuum wavelength 632.8 nm. Find its (b)
  wavelength, (c) frequency, and (d) speed in the
  solution

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PROBLEM1.4

• Find the speeds of light in (a) flint glass, (b)
  water, and (c) zircon.

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PROBLEM1.5

• Light of wavelength ?0 in vacuum has a wavelength
  of 438 nm in water and a wavelength of 390 nm in
  benzene. (a) What is the wavelength ?0 of this
  light in vacuum? (b) Using only the given
  wavelengths, determine the ratio of the index of
  refraction of benzene to that of water.

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PROBLEM1.6

• Light of wavelength 436 nm in air enters a
  fishbowl filled with water, then exits through
  the crown-glass wall of the container. Find the
  wavelengths of the light (a) in the water and (b)
  in the glass.

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PROBLEM1.7

• A ray of light is incident on the surface of a
  block of clear ice at an angle of 40.0 with the
  normal. Part of the light is reflected and part
  is refracted. Find the angle between the
  reflected and refracted light.

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PROBLEM1.8

• A narrow beam of sodium yellow light (?0 589
  nm) is incident from air on a smooth surface of
  water at an angle of ?1 35.0. Determine the
  angle of refraction ?2 and the wavelength of the
  light in water.

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PROBLEM1.9

• A beam of light, traveling in air, strikes the
  surface of mineral oil at an angle of 23.1 with
  the normal to the surface. If the light travels
  at 2.17 108 m/s through the oil, what is the
  angle of refraction?

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PROBLEM 1.10

• The index of refraction for red light in water is
  1.331, and that for blue light is 1.340. If a ray
  of white light enters the water at an angle of
  incidence of 83.00, what are the underwater
  angles of refraction for the blue and red
  components of the light?

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PROBLEM1.11

• A certain kind of glass has an index of
  refraction of 1.650 for blue light of wavelength
  430 nm and an index of 1.615 for red light of
  wavelength 680 nm. If a beam containing these two
  colors is incident at an angle of 30.00 on a
  piece of this glass, what is the angle between
  the two

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PROBLEM1.12

• Calculate the critical angles for the following
  materials when surrounded by air (a) zircon, (b)
  fluorite, (c) ice. Assume that ? 589 nm.

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PROBLEM1.13

• For 589-nm light, calculate the critical angle
  for the following materials surrounded by air
  (a) diamond and (b) flint glass.

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PROBLEM1.15

• A beam of light is incident from air on the
  surface of a liquid. If the angle of incidence is
  30.0 and the angle of refraction is 22.0, find
  the critical angle for the liquid when surrounded
  by air.

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PROBLEM1.16

• A layer of ice, having parallel sides, floats on
  water. If light is incident on the upper surface
  of the ice at an angle of incidence of 30.0,
  what is the angle of refraction in the water?