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PHYSICS
COURSE CODE: PH101
COURSE MATERIALS
1. PHYSICAL OPTICS 2. RELATIVITY3. RADIATION4. ATOMIC STRUCTURE5. STATISTICAL DISTRIBUTIONS6. LASERS
TEACHING PROCESS
The whole course will be covered through1. Lectures2. Tutorials3. Laboratory
The topics will be covered in the lectures. Assignments in the form of Questions will be given.
Students have to complete the assignmentsthrough discussion in tutorials.
Class tests will be conducted during tutorials.
Evaluation scheme
There will be three tests all over the semester.
20 marks for the Test-I.25 marks for the Test-II.30 marks for the TEST-III.
25 marks for internal assessment and class tests.
100 marks for the laboratory work.Evaluation will be done through regular assessment of practical and viva-voca.
BOOKS:
• OPTICS, Eugene Hecht, Pearson Education.
• OPTICS, Ajay Ghatak.
• Fundamental of Optics, Jenkins & White.
• A. Beiser, Concepts of Modern Physics,
Optical Recording
• Media types:– Compact Disc (CD)– Digital Video/Versatile Disc (DVD)
• Reading technique:– Reflect laser light from optical surface– Measure reflected intensity to obtain
information
Techniques
• Laser light is focused on disc aluminum layer
• Reflection is weaker from ridge than flat
• Reflected light is directed to photodiodes
• Light intensity indicates ridges or flats
Most of the above applications need some optical phenomena
Interference, Diffraction, Polarization
Physical Optics
OPTICS
Physical Optics
Wave nature of light
Interference Diffraction Polarization
Waves All Around Us!
Waves are everywhere. Sound waves, visible light waves, radio waves, microwaves, water waves, sine waves, cosine waves, telephone chord waves etc.
There are a variety of phenomenon in our physical world which resemble waves so closely that we can describe such phenomenon as being wavelike.
A wave is a disturbance that propagates, carrying energy, which can travel through either in a medium or through vacuum, waves can transfer energy from one place to another without any displacement of the particles of the medium.
Wave
Waves are characterized by crest (highs) and trough(lows)
THERE ARE TWO TYPES OF COMMON WAVES.
I) SOUND WAVE
II) LIGHT WAVE
waves of various frequencies; the lower waves have higher frequencies than those above.
Frequency is the measurement of the number of times that event occurs repeatedly per unit time. To calculate the frequency, one fixes a time interval, counts the number of occurrences of the event within that interval, and then divides this count by the length of the time interval.
Amplitude is a nonnegative scalar measure of a wave's magnitude of oscillation. The y is the amplitude of the wave.
The wavelength is the distance between repeating units of a wave pattern
PhaseThe phase of a wave relates the position of a feature, typically a peak or a trough of the waveform, to that same feature in another part of the waveform.
positions of the peaks (X), troughs (Y) and zero-crossing points (Z) coincide. The phase difference of the waves is thus zero
The phase difference between two signals of the same frequency can be thought of as a delay or advance in the start of one signal's cycle with respect to another.
Phase difference is expressed in degrees from 0 to 360. If the difference is 180 degrees then the two signals are said to be in antiphase: they are equal but opposite, and if added together will sum to zero. If the phase difference is 90 degrees then the signals are said to be in quadrature.
Phase difference and path difference• If the phase difference between two waves is 2
then the path difference between that two waves is .
• Let for a path difference x, the phase difference is .
• We know that
for a path difference , phase difference = 2 so, for path difference x, the phase difference =
x2
So, phase difference = differencepath 22
x
Angular frequency
angular frequency ω (also called angular speed) is a scalar measure of rotation rate.
Angular frequency is a measure of how fast an object is rotating
• The period T of the motion is the time taken for the particle to go through one full circle.
T = 2/• Frequency f =1/T
What is light?
Electromagnetic radiation of any wavelength.
The three basic dimensions of light :
•intensity (or amplitude, perceived by humans as the brightness of the light),
•frequency (or wavelength, perceived by humans as the color of the light),
•polarization (or angle of vibration and not perceptible by humans under ordinary circumstances)
PRINCIPLE OF SUPERPOSITION
principle of superposition states that the net displacement at a given place and time caused by two or more waves traversing the same space is the vector sum of the displacements which would have been produced by the individual waves separately.
Two wave pulses are travelling, one is moving to the right, the other is moving to the left. They pass through each other without being disturbed, and the net displacement is the sum of the two individual displacements.
COHERENT SOURCESSources emitting light waves of the same frequency, nearly same amplitude and are always in phase with each other or having a constant phase relationship between them, means that two sources must emit radiations of the same wavelength.
In practice it is not possible to get independent Two sources which are coherent. But two virtual Sources formed from one single source can act as Coherent source.
Two ways to get coherent source•Division of wave front : waves from two sources are formed from a single source
Division of amplitude : waves from two sourcesare formed from a single source due to reflection and Refraction. One of these source is real other virtual source
P
D
S
Monochromaticsource
S1
S2
Virtualsource
DIVSION OF WAVE FRONT
a
b
c
d
I II
DIVISION OF AMPLITUDE
INTERFERENCE
Interference is the superposition of two or more coherent waves resulting in a new wave pattern.
There are two types of interference: Constructive Interference Destructive Interference
Conditions of Interference
•The interfering waves should be coherent
•The interfering waves must be of same wavelengths
•Two waves must have the same state of polarization to get fringes of maximum contrast
Constructive and destructive interference
If the two waves have the same amplitude A and wavelength the resultant waveform will have amplitude between 0 and 2A depending on whether the two waves are in phase or out of phase.
If the two waves are in phase, interference will be constructive.If the two waves are out of phase, interference will be destructive.
Two waves that are in phase,with amplitudes A1
and A2. Their troughs and peaks line up and the
resultant wave will have amplitude A = A1 + A2.
This is known as constructive interference.
If the two waves are 180° out of phase, then one wave's crests will coincide with another wave's troughs and so will tend to cancel out. The resultant amplitude is A = |A1 − A2|. If A1 = A2
the resultant amplitude will be zero. This is known as destructive interference.
combinedwaveform
wave 1
wave 2
Two waves in phaseTwo waves 180° outof phase
S1
S2
L
P
O
D
d
yn
d/2
d/2
Let y1 and y2 are the displacements of two waves coming from
S1 and S2
tay
tay
cos
cos
2
1
is the phase difference between two waves reaching At P from S1 and S2, a be the amplitude of wave.
)2
cos(2
cos2
2cos
2cos2
)cos(cos21
wta
wtwtwtwta
tatayyy
waveresultant theof amplitude2cos2 a
amplitude of square is
intensity2cos4 22 aI
)maxima(4
;..2,,0 differencepath or
2,..4,2,0
2aI
nx
nif
)minima(0
;2
)12(..
2
3,
2 differencepath
)12,..(3,
I
nx
nif
In each case n = 0,1,2….
)(221
4
2cos4
2222
22
aaaa
aI
For incoherent light
= sum of intensityof constituent waves.
Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). As time progresses, the wave fronts would move outwards from the two centers, but the dark regions (destructive interference) stay fixed.
Young’s Double slit experiment
Experiment consists of letting light passes through two slits producing fringes on a screen. These fringes or interference patterns have light and dark regions corresponding to where the light waves have constructively and destructively interfered.
(The experiment can also be performed with a beam of electrons or atoms, showing similar
interference patterns.
L
P
d
S1
S2
O
D
yn
d/2
d/2
At point P for maxima we must have S2P – S1P = n, n = 0,1,2,3…
THE INTERFERENCE FRINGES
])2
([)( 2222
dyDPS n
])2
([)( 2221
dyDPS n
])2
([])2
([
)()(
2222
21
22
dyD
dyD
PSPS
nn
)()(
2)()(
2)()( thus,
2
12
12
2
1
2
2
2222
PSPS
dyPSPS
dyPSPS
dy
dyyDdyyD
n
n
n
nnnn
If d<D then S2PS1PD and thus S2P+S1P=2D
D
dynor
D
dy
D
dyn
n
nn
,
2
2 therefore,
d
Dny
n
d
Dy
d
Dy
d
Dy
d
Dny
n
3
2
3
2
1
d
Dyy
d
Dd
D
d
D
d
D
d
D
nn
yyyy
1
2312
or,
232
..3,2,1,0,2
)12(
fringes,dark for Similarly
12 nnPSPS
So we get, for dark and bright fringes
Distance between any two consecutive bright fringes
d
Dny
d
Dny nn
;
2
)12(
d
Dny
d
Dny nn
;
2
)12(
d
D
d
Dyn
d
D
d
Dyn
d
Dyn
2;
2
5,2
;2
3,1
0;2
,0
2
1
0
d
D
d
D
d
Dyy
2
3
2
512
Fringe width
d
D
Fringe width
Seperation between dark and bright fringes
d
d
d
d
d
d
2
2
3
O is equidistant from S1 and S2 so light waves superposedat O are in phase so light intensity at O will be maximum.
• At O we observe the central bright fringe. For this fringe n=0 y = 0. so central bright fringe will be referred as zeroth order bright fringe.
• At n=1 we have y= 1D/d, this is the first order bright fringe.
• At n=0 we observe first dark fringe at y = D/2d.
So at n=0 we have the first order dark fringe.
Dark areas = Troughs (valleys)Light aresa = Crests (peaks)
