NITRKL

2. PH 101: PHYSICS - I [3-1-0]
LA-118
Tuesday-Friday (4.15 -5.15 PM)
Dr. Jyoti Prakash Kary
Department of Physics
National Institute of Technology
Rourkela
[Office:MB 229, Ph: 2732, Email: karjp@nitrkl.ac.in]

3. Topics
Wave optics, Interference, Diffraction, Polarization
Special Relativity, Particle properties of Waves, Wave
properties of Particles, Quantum Mechanics.p p
Mark Distributions:
Mid Term: 30%
GRADE Distributions:
 90  ExMid Term: 30%
End Term: 50%
TA: 20%
 90  Ex
 80  A
 70  B
 60  C 60  C
 50  D
 35  P
< 35 FAILTA: ATTENDANCE (5) < 35  FAILTA: ATTENDANCE (5)
ASSIGNMENTS (10)
BEHAVIOUR/ATTITUDE (5)
(If you will request me to illegally enhance your marks and attendance :
- 10 marks )

4. Assignments
Assignment-1 Assignment-2 Assignment-3 Assignment-4 Assignment-5
51 2 3 4
Assignments
of PH-101
Assignments
of PH 101
Assignments
of PH 101
Faculty: Dr. J.P. Kar
Name: XYZ
Faculty: Dr. J.P. Kar
Name: XYZ
Roll no : 0000
Faculty: Dr. J.P. Kar
Name: XYZ
Roll no : 0000Name: XYZ
Roll no.: 0000
Date: 00.00.2012
Roll no.: 0000
Date: 00.00.2012
Roll no.: 0000
Date: 00.00.2012

5. Assigned Part
Optics: (i) Interference: Condition for interference, Division of wave
front (two beam interference): Young's double slit experiment fringefront (two beam interference): Young s double slit experiment, fringe
pattern on transverse and longitudinal planes, intensity distribution,
Fresnel's biprism, displacement of fringes; Division of amplitude (two
beam interference): cosine law, Newton's rings experiment, Michelson
Interferometer, fringes of equal inclination and equal thickness. (ii), g q q ( )
Diffraction: Fraunhofer, Fresnel's diffraction, single slit (infinite beam
interference), two and N slits( Grating) Fraunhofer diffraction pattern
and intensity distributionand intensity distribution.

6. Books
[1] Fundamentals of Optics, F. A. Jenkins, H. E. White, Tata McGraw-Hill
(2011)(2011).
[2] Optics, A. Ghatak, Tata McGraw-Hill (2011).
[3] A Textbook of Optics, N. Subrahmanyam, B. Lal, M. N. Avadhanulu,
S. Chand and company (2012).
[4] Geometrical and Physical Optics, P. K. Chakrabarti, New Central
Book Agency (2009).g y ( )
WEB REFERENCES
1.www. google.co.in1.www. google.co.in
2.http://en.wikipedia.org
3.www.youtube.com

7. Optics (light wave)
• Interference
• Diffraction• Diffraction
•Polarization

8. Why Optics ?
• Windows
• Camera
• Display System
• Microscope and TelescopesMicroscope and Telescopes
• Solar Cell
• Light Emitting Diodes (LED)• Light Emitting Diodes (LED)
• X-ray, LASER
M t i l Ch t i ti (UV Vi ibl t FTIR PL t )• Material Characterization (UV-Visible spectroscopy, FTIR, PL etc)
• Remote Sensing
• Signal processing (optical fiber)
• Bio-medical applications

9. Optics
Optics is the branch of physics which involves the behaviour
and properties of light including its interactions with matter and theand properties of light, including its interactions with matter and the
construction of instruments that use or detect it.
G i l i ( i ) Li h ll i f h lGeometrical optics (ray optics): Light as a collection of rays that travel
in straight lines and bend when they pass through or reflect from
surfaces.
Physical optics (wave optics): It includes wave effects such as
diffraction and interference that cannot be accounted for in
geometrical optics.
HistoryHistory
The word optics comes from the ancient Greek word ὀπτική, meaning
appearance or look.
Optics began with the development of lenses by the ancient Egyptians
and Mesopotamians as early as 700 BC.
The ancient Romans and Greeks filled glass spheres with water to
make lenses.

10. Continued….
In Italy, around 1284, Salvino D'Armate invented the firsty, ,
wearable eyeglasses. This was the start of the optical industry of
grinding and polishing lenses for these "spectacles“ in Venice and
Florence.Florence.
In the early 17th century Johannes Kepler expanded on
geometric optics through reflection by flat and curved mirrors and thegeometric optics through reflection by flat and curved mirrors and the
optical explanations of astronomical phenomena such as lunar and
solar eclipses. He was also able to correctly deduce the role of the
ti th t l th t d d iretina as the actual organ that recorded images.
Until middle of 17th century: light consisted of a stream of corpuscles
(Newton)
Middle of 17th century: Wave motion of lighty g
1670: Reflection and refraction of light by wave theory (Huygen)
1663-1665: Diffraction (Grimaldi, Hooke)
1827: Interference (Young, Fresnel)1827: Interference (Young, Fresnel)
1873: Electromagnetic nature of light (Maxwell)
1901: Quantization of light (Planck)

11. Light Wave

12. Light Wave
C = λ × f E = h × fC = λ × f
Where
E = h × f
WhereWhere,
C = velocity of light (3 ×108 m/s)
λ = wavelength of light
f = frequency of light
Where,
E = light energy
h = Planck’s constant
= 6 626 x 10-34 joule secondf = frequency of light = 6.626 x 10 34 joule.second
f = frequency of light
Long wavelength (Low frequency) Short wavelength (High frequency)

13. Lights of different color
RED
ORANGE
Long wavelength
(L f )ORANGE
YELLOW
(Low frequency)
GREEN
BLUEBLUE
INDIGO Short wavelength
(High frequency)
VIOLET
(High frequency)
Violet light has higher energy

14. Interference of light
Interference is a phenomenon in which two coherent lightp g
waves superpose to form a resultant wave of greater or lower
amplitude.
Types of interference
interference patterns - Shortcut.lnk Wave Interference - Shortcut.lnk
Types of interference
(a) Constructive interference: If a crest of one wave meets a crest of
another wave, the resultant intensity increases.
(b) Destructive interference: If a crest of one wave meets a trough of( ) g
another wave, the resultant intensity decreases.

15. Conditions for Interference
[1] The two interfering waves should be coherent, i.e. the phase
difference between them must remain constant with time.
[2] The two waves should have same frequency.
[3] If Interfering waves are polarized, they must be in same state of[3] If Interfering waves are polarized, they must be in same state of
polarization.
[4] The separation between the light sources should be as small as[4] The separation between the light sources should be as small as
possible.
[5] Th di t f th f th h ld b it l[5] The distance of the screen from the sources should be quite large.
[6] The amplitude of the interfering waves should be equal or at least
very nearly equal.
[7] The two sources should be narrow
[8] The two sources should give monochromatic or very nearly
monochromatic, or else the path difference should be very small.

16. Locus (Mathematics)
In geometry, a locus is a collection of points according to
certain principles.p p
Example: A circle may be defined as the locus of points in a plane (2D)Example: A circle may be defined as the locus of points in a plane (2D)
at a fixed distance from a given point (centre).

17. Wavefront
In physics, a wavefront is the locus of points having the same
phase (line or curve in 2D, or a surface for a wave propagating in 3D)p ( , p p g g )
2-Dimensional 3-Dimensional

18. Thomas Young
Screen
Interference of light by
Young's Double Slide Experiment.lnk
* In 1801, Young admitted the sunlight through a single pinhole and then
di d h i li h i h l
division of wavefront
directed the emerging light onto two pinholes.
* The spherical waves emerging from the pinholes interfered with each other
and a few colored fringes were observed on the screen.
* The pinholes were latter replaced with narrow slits and the sunlight was
replaced by monochromatic light ( Ex: Sodium lamp, Yellow, 5893 Å)

19. Interference of Light by Division of Wavefront
Light sourceLight source
Single slit
Double slitDouble slit
(S1, S2)
Interference
pattern on dark
film (screen)( )
Intensity
distribution

20. Caluculation of optical path difference between two waves
As slits (S1 and S2) are equidistant from source (S), the phase of the wave at
S1 will be same as the phase of the wave at S2 and therefore, S1,S2 act asS1 will be same as the phase of the wave at S2 and therefore, S1,S2 act as
coherent sources. The waves leaving from S1 and S2 interfere and produce
alternative bright and dark bands on the screen.
P
x
G
OS M
G
2d
H
Let P is an arbitrary point on screen, which is at a distance D from the double
slits
ScreenYoung’s double slit experiment
slits.
2d is the distance between S1 and S2
θ is the angle between MO and MP
i th di t b t O d Px is the distance between O and P
S1N is the normal on to the line S2P
MO bisects S1S2 and GH (i.e. S1M = S2M = GO = HO = d)

21. Continued…..
P
x
G
OS M
H
2d
Screen
H
The optical paths are identical with the geometrical paths, if the
experiment is carried out in airexperiment is carried out in air.
The path difference between two waves is S2P-S1P = S2N
Let S1G and S2H are perpendiculars on the screen and from S2HP
t i ltriangle
(S2P)2 = (S2H)2 + (HP)2
= D2 + (x+d)2= D2 + (x+d)2

22. Continued…..
Since D>>(x+d) (x+d)2/D2 is very smallSince D>>(x+d), (x+d) /D is very small
After expansion,
Path difference = S2P-S1P
[(A+B)2 –(A-B)2 = A2 + B2 + 2AB –(A2+B2-2AB) = 4AB]

23. Continued…..
The nature of the interference of the two waves at P depends simply
on how many waves are contained in the length of path difference
(S2N).
• If the path difference (S2N) contains an integral number of
wavelengths, then the two waves interfere constructively producing a
maximum in the intensity of light on the screen at P.
• If the path difference (S2N) contains an odd number of half-
wavelengths then the two waves interfere destructively and producewavelengths, then the two waves interfere destructively and produce
minimum intensity of light on the screen at P.

24. Continued…..
Thus for bright fringes (maxima),
F d k f i ( i i )For dark fringes (minima),
Let xn and xn+1 denote the distances of nth and (n+1)th bright fringes.
ThenThen,

25. Continued…..
Spacing between nth and (n+1)th bright fringe is
H th i b t ti b i ht f i i thHence, the spacing between any consecutive bright fringe is the same.
Similarly, the spacing between two dark fringes is Dλ/2d,
The spacing between the fringes is independent of n
The spacing between any two consecutive bright or dark fringe is
called the “fringe width” and is denoted by

26. PROBLEM-1
Q: In an interference pattern, at a point we observe the 12th order
maximum for λ1= 6000 Å. What order will be visible here if the source1
is replaced by light of wavelength λ2= 4800 Å ?
A: In double slit interference, the distance x of a bright fringe from the
t ( d f i ) icentre (zero-order fringe) is
x = (D/2d)nλ, where n = 0,1,2,….
Thus at a given point nλ is constant
Or, n1λ1 = n2λ2
n2 = n1λ1/λ2 = 12 x 6000/4800 = 15

27. PROBLEM-2
Q: Two straight narrow parallel slits (2 mm apart) are illuminated with
a monochromatic light of wavelength 5896 Å. Fringes are observed at
a distance of 60 cm from the slits. Find the width of the fringes?
A: The interference fringe-width for a double slit is given by
2d 2 0 22d = 2 mm = 0.2 cm,
D = 60 cm,
λ = 5896 Å = 5896 x 10-8 cm
Fringe-width = (60 cmx 5896 x 10-8 cm)/ 0.2 cm = 1.77 x 10-2 cm

28. PROBLEM-3
Q I t lit i t f tt ith λ 6000 Å th d dQ: In a two-slit interference pattern with λ = 6000 Å the zero-order and
tenth-order maxima fall at 12.34 mm and 14.73 mm, respectively. If λ is
Åchanged to 5000 Å, deduce the positions of the zero-order and
twentieth-order fringes, while other arrangements remaining the same.
A: Fringe-width is
with λ = 6000 Å the distance between zero order and tenth orderwith λ = 6000 Å, the distance between zero-order and tenth-order
fringe is 14.73 mm - 12.34 mm = 2.39 mm
F i idth 2 39 /10 0 239Fringe-width = 2.39 mm/10 = 0.239 mm
(Fringe-width)6000/ (Fringe-width)5000 = 6000 Å /5000 Å = 6/5
(Fringe-width)5000 = (Fringe-width)6000 x 5/6 = 0.239 mm x 5/6 = 0.199 mm
Position of zero-order fringe (for λ = 5000 Å) = 12.34 mm
Position of twentieth-order fringe (for λ = 5000 Å)
= 12.34 mm + (0.199 mm x 20) = 16.32 mm