Physics-II
Physics
INTERFERENCE UNIT-I
INTRODUCTION
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•
•
•
•
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Coherent sources
Coherent
sources
Conditions for sustained interference
Di i i
Division of wave front‐
f
f t Fresnel’s biprism
F
l’ bi i
Division of amplitude – wedge‐ shaped film
Newton’s ring
Michelson interferometer and its applications
Michelson interferometer and its applications
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Lecture ‐1
• Coherent sources‐
• If two sources are emitting light to be coherent with same amplitude, same wavelength , same frequency, same velocity, l
h
f
l
same starting phase etc. then the sources are said to be coherent
said to be coherent.
• Methods of production of coherent sources
• (i) Young’s double slit method
(i)
’ d bl li
h d
• (ii) Bi‐prism method vaishali.dixit@ggnindia.dronacharya.info
Interference Interference
• When
When two waves superimposed the resultant two waves superimposed the resultant
displacement is the vector sum of the individual displacement.
• When due to interference resultant amplitude becomes maxima .we call it as constructive interference
• If superposition causes the minimum resultant amplitude we consider it as destructive interference
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Assignment 1
Assignment‐1
1.What are the coherent sources?
2.How you can produce coherent sources?
3. What is constructive and destructive interference?
destructive interference? vaishali.dixit@ggnindia.dronacharya.info
LECTURE‐2
Superposition of Waves
Superposition of Waves Consider a region in space where two or more waves
where two or more waves pass through at the same time. According to the superposition principle, the net displacement is simply t di l
ti i l
given by the vector or the algebraic sum of the individual displacements. p
Interference is the combination of two or more waves to form a composite wave based on such
wave, based on such principle. The idea of the superposition principle is illustrated vaishali.dixit@ggnindia.dronacharya.info
PHASE‐SHIFT=EXTRA PATH?
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Young’s Double‐Slit Experiment
constructive and destructive interference
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LECTURE‐3
Young’s Double‐Slit Experiment ’
bl l
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Path difference, position of bright & dark fringes and band width
d b d id h
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LECTURE‐4
Fresnel’s biprism
l’ b
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LECTURE‐5
Determination of 2d
f d
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Long question
Long question
• Explain
Explain the formation of interference fringes the formation of interference fringes
by means of Fresnel’s biprism when a monochromatic source of light is used How
monochromatic source of light is used. How will you measure the wavelength of mono‐
chromatic light using biprism method
chromatic light using biprism
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Assignment‐2
• In
In the interference pattern ,at a point we the interference pattern at a point we
observe the 12th order maxima for wave –
length λ1 = 6000 A
length λ
= 6000 Ao .What order will be visible What order will be visible
here if source is replaced by light of wavelength λ2 = 4800 A
wavelength λ
4800 Ao
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MICHELSON’S INTERFEROMETER
LECTURE‐6
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Long questions
Long questions
• Describe
Describe the construction and working of the construction and working of
Michelson interferometer ? How is this interferometer used for determining wave
interferometer used for determining wave length of light and the standardization of a meter?
• Describe the construction, principle, theory and working of Michelson interferometer to
and working of Michelson interferometer to find the thickness of a thin transparent plate.
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Assignment‐3
• A
A transparent film of glass of refractive index transparent film of glass of refractive index
1.5 is Introduced normally in the path of one of the interfering beams of Michelson
of the interfering beams of Michelson interferometer which is illuminated with light of wavelength 5000 Ao .This causes 600 dark of wavelength 5000 A
This causes 600 dark
fringes to sweep across the field. Find the thickness of the film
thickness of the film . vaishali.dixit@ggnindia.dronacharya.info
LECTURE‐7
NEWTON’S RINGS
’
• When a plano‐convex lens with its convex surface e a p a o co e e s t ts co e su ace
is placed on a plane glass sheet, an air film of gradually increasing thickness outward is formed b
between the lens and the sheet. The thickness of h l
d h h
h h k
f
film at the point of contact is zero. If monochromatic light is allowed to fall normally on
monochromatic light is allowed to fall normally on the lens, and the film is viewed in reflected light, alternate bright and dark concentric rings are seen g
g
around the point of contact. These rings were first discovered by Newton, that's why they are called NEWTON'S RINGS
NEWTON'S RINGS .
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Newton’ss rings
Newton
rings
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Assignment 4
Assignment‐4
• In a Newton’s ring experiment the diameter of the 15th ring was found to be 0.59 x 10‐2 m and that of the 5th ring was 0.336x10‐2 m . If the radius of the Plano convex lens is 1m, calculate the wave length of light used.
• What change would you expect in p
g
interference pattern of Newton’s rings if transparent plate below the lens is replaced by a plane mirror ?
y p
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Assignment‐5
• A
A convex surface of radius 3m of a Plano
convex surface of radius 3m of a Plano‐
convex lens rests on a concave spherical surface of radius 4m and Newton’ss rings are surface of radius 4m and Newton
rings are
viewed with reflected light of wavelength 6x10‐2 m . Calculate the diameter of the 13
m Calculate the diameter of the 13th
bright ring.
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Long question
Long question
• What
What are Newton
are Newton’ss rings ? Describe and rings ? Describe and
explain the formation of Newton’s ring in reflected mono – chromatic light .Prove that reflected mono chromatic light Prove that
diameter of bright rings are proportional to the square root of odd natural numbers
the square root of odd natural numbers. vaishali.dixit@ggnindia.dronacharya.info
Long question
Long question
• Discuss
Discuss the formation of newton
the formation of newton’ss ring by ring by
(i)reflected light (ii) transmitted light . Drive an expression for diameter of nth dark ring in
expression for diameter of nth dark ring in reflected light ?
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