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Applied Optics
Dr D. Arun Kumar
Assistant Professor
Department of Physical Sciences
Bannari Amman Institute of Technology Sathyamangalam
LIGHT AS A WAVE
• Light has dual nature. It has both particle nature and
wave nature but it cannot act as a wave and particle
simultaneously.
• Light is also having the properties such as reflection,
refraction, interference, diffraction, polarization.
• Light is also having two most famous effects like
photoelectric effect and Compton Effect.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
• To explain the properties like interference diffraction
and polarization we need to adopt wave nature for light.
• Light is a transverse wave.
• The first person to advance a convincing wave theory for
light was DUTCH PHYSICIST CHRISTIAN HUYGENS, in
1678.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
LIGHT AS A WAVE
Representation of Light wave
• Whose displacement is given b
• y=asinωt
• Where ' a' is amplitude of wave.
• 'ωt' is Phase, Which gives the position and direction of wave at a time 't'
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
PHASE DIFFERENCES:
• The angular separation between two
points of wave is called Phase
difference.
• It is measured in radians or degrees.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
PATH DIFFERENCE:
• The linear separation between two
points of wave is called Path Difference
• It is measured in mm or cm.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
RELATION BETWEEN PHASE DIFFERENCE AND PATH DIFFERENCE:
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
INTERFERENCE:
• Interference is the optical phenomenon
in which brightness and darkness are
produced by the combination of two
similar light waves.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
• When two light waves of same frequency having constant
phase difference coincide in space and time. There is
modification in the intensity of light.
• This modification in the intensity is due to superposition
of two light waves are called Interference.
• And the pattern dark and bright fringes produced are
called Interference pattern.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
INTERFERENCE:
TYPES OF INTERFERENCE:
Interference is of two types.
• Constructive interference / constructive superposition
• Destructive interference / destructive superposition
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
CONSTRUCTIVE INTERFERENCE:
• When crust of one light wave falls on the crust of another
wave then the resultant intensity increases
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
DESTRUCTIVE INTERFERENCE:
• When crust of one light wave falls on the trough of
another wave then the resultant intensity decreases.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Conditions for sustained or Good interference pattern :
• We require two monochromatic light sources.
• These two sources must be coherent i.e., they constant
phase difference.
• The frequency must be the same.
• The amplitude must be the same.
• They must travel in the same directions.
• The two sources must be the same
• These two sources must be as near as possible and the
screen must be as far from them as possible.
Interference at a wedge shaped films
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Determination of thickness of a paper or wire
• Two optically plane glass plates are placed one over the other and tied at one end. The given wire is introduced near the other end, so that an air wedge is formed.
• The distance between the wire and the tied end (L) is measured using a scale.
• Light from a sodium vapour lamp is incident on a plane glass plate inclined at 45 to the horizontal.
• The reflected light from the plane glass plate is incident normally on the optically plane glass plates forming the air wedge and reflected back.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Determination of thickness of a paper or wire
• The reflected light from the air-wedge is viewed through the eye-piece of a microscope. The microscope is moved up and down and adjusted for clear interference fringes of alternate dark and bright.
• The microscope is fixed so that the vertical cross-wire coincides with the dark band (say nth band) and the reading is noted.
• The microscope is moved across the fringes and readings are noted when the vertical cross-wire coincides with the (n+5)th, (n+10)th….. dark bands.
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Determination of thickness of a paper or wire
• The observed readings are tabulated and the band width () is calculated.
• The thickness of the given wire/thin-sheet is calculated using the formula.
t = L/2 (m)
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam
Order
of
Fringes
Microscope reading Width for 5
fringes
(10-2 m)
Fringe width
(10-2 m)
MSR
(10-2 m)
VC
(div)
TR
(10-2 m)
Determination of thickness of a paper or wire
Testing of flatness of a surface
Department of Physical Sciences, Bannari Amman Institute of Technology, Sathyamangalam