wave optics Flashcards
hugen wave theory {5}
- light travels in form of wavefront
- all particles in wavefrom will be in same phase
- wavefront travels in forward drxn
- wavefront travels wiith speed of light
- in isotropic medium speed in same in all drxn
types of source - point, linear,exnteded source at a very long distance
type of wavefront?
variation of A with r?
variation of I with r?
- a dp 1/r , i dp 1/r^2
- a dp 1/rootr r , i dp 1/r
- a const. , i const
interfernce of light wave
at x = 0
y1 = a1sin0
y2 = a2sin0+cos0
on superimposing these two waves the net amplitude we get is
Anet = root a1^2 + a2^2 + 1a1a2cos0
Inet = i1 + i2+ 2root i1 root i2 cos 0
if a1=a2 Anet = 2Acos0/2
if i1 = i2 Inet = 4Icos^2 0/2
contructive interfernece
1. phase diff
2. path diff
3. cos0
4. Anet
5. Inet
6. Anet Inet if A1=A2 and i1=i2
- 2n pie[even]
- n lemda [continuous]
- 1
- a1 +a2
5.
[root i1+ root i2] ^2
6 Anet = 2A
Inet = 4I
destructive interfernce
1. phase diff
2. path diff
3. cos0
4. Anet
5. Inet
6. Anet Inet if A1=A2 and i1=i2
- (2n-1)pie [ odd]
- (2n-1) lemda/2 [odd]
- -1
- Anet = AI - A2
- Inet =[root i1 - rooti2] ^2
6.Anet = 0
Inet = 0
coherent source
same frequency
const phase diff
incoherent source
not same frequency
not const phase diff
two independent sources are incoherent
methods to obtain coherent source
1, ydse
2. division of amplitude
YDSE
when two coherent sources are used intensity changes at different points
- fringe width
- angular fringe width
- d
- D
- tan0
- sin0
- x
- y
- diagram
notes pg 7,8
for constructive
1. y =
for destructive
y =
notes pg 9
path diff and phase diff
1. centre maxima
2. 2st minima
3. 1st maxima
notes pg 9
YDSE in medium
2 formulae
lemda m =
beta m =
YDSE in medium - if complete appratus is immersed in medium refractive index [mew]
lemda m = lemda air / mew
beta m = beta air/ mew
effect of film in YDSE
1. optical path
2. distance travel in vaccum
3. path diff
4. time
6. const
7. destruc
8. y =
9. no. of fringeshift n =
10. diagram
- optical path - distance travel in medium in same time as vacuum
- distance travel in vaccum - t
- path diff = (mew -1)t
- time = dist/ speed
- const -
(mew -1)t = nlemda - destruc -
(mew -1)t = (2n-1)lemda/2 - y = (mew -1)tD/ d
- no. of fringeshift n = (mew -1)t/ lemda
- diagram
1.if 2 slabs are used {mew} =
2. where will pattern shift
- {(mew 1-1)t1 - (mew2 -1)t2}
- shift towards larger (mew -1)t
- Iavg
- fringe visibility [v]
- fringe visibility max =
- if we change monochromatic light to white light wht happens to all fringes
- Iavg
- fringe visibility [v] pg 19
- fringe visibility max = Imin is zero
- if white light is used instead of monochromatic light then
- central fringe will be white
- all fringes will be colourful with outer part red
- fringe width max for -
- fringe width min for -
why does soap bubble] [oil film] loooks colourful ?
division of A
path diff -
r -
- due to division of amplitude interference of thin film [soap bubble] [oil film] loooks colourful
path diff - 2 mewt cosr
r - angle of refraction
- wht happens when thin film is kept in front of slit?
- interference in based on ?
- when thin film is kept in front of slit,
- fringe width doesnt change
- only fringe pattern shifts
- if net path diff is not zero - energy consv.
transmitted ray system -
1. max =
2. min =
reflected ray system -
1. max =
2. minima =
transmitted ray system -
1. max =
2mewt cosr = n lemda
2. min =
2mewt cosr =
(2n +1) lemda/2
reflected ray system -
1. max =
2mewt cosr = 2n +1 lemda/2
2. minima =
2mewt cosr = n lemda
how many fringe width are produced in YDSE
in interfernce in YDSE
- infinte no. of fringes
- fringes of equal width and intensity of all maxima will be same
wht is diffraction?
- diffraction is the bending of light
- from any sharp edged opaque object
- or spreading of light geometrically though an aperture
- deviation of light from rectilinear path is k/a diff
- 2 diagrams
size of obstacle
a = lemda
a/ lemda approx = 1
why do soundwaves show more diffraction then light rays
bcuz wavelength of light is 10^ -7m [very smaall]
diff. of ultrasonic waves is not easily obserevd bcuz?
thier wavelength is order of 1cm
diffraction of radiowaves is easily obsereved becoause ?
have large wavelength
fraun hoffer diffraction using one slit
1. delta x =
2. for minima
- maxima
- delta x = asino
- for minima
asino = n lemda - maxima
asino = (2n+1) lemda/2
central maxima
1. y =
2. central fringe width =
3. remainig fringe width =
distance bw each side of maxima is central fringe width
central maxima
1. y = lemda D/a
2. central fringe width = 2lemda D/a
3. remainig fringe width =
lemda D/a
angular fringe width
1. central angular fringe width =
=
- other angular fringe width
=
angular fringe width
1. central angular fringe width = 2theta
= 2lemda/ a
- other angular fringe width
= lemda / a
other names for theta
- angular position
- diffracting angles
central fringe width specail case
2lemda*f/ a
intensity curve
notes pg 36
difference bw interference and diffraction
notes pg 39
path difference due to mew
- delta x =
- mew relative =
path difference due to mew
- delta x =
(mew relative - 1)t
- mew relative =
mew slab/ mew medium
- wht is polarisation?
- no intensity =
- max intensity =
- wht we understnad form it ?
- restricting the vibration of light in particular direction
- 90 degree
- zero degree
- light is transeverse wave
polariser?
- tournmaline crystal
- nicol priism
- polaroid
plane polarised light -
unpolarised light -
plane polarised light - Io/2
unpolarilased light - Io
Law of malus 2 laws
- I1 = Io/2
- I2 = I1 cos^2O
brewester law
tanOp = mew
Op + Or = 90 degree
methods to obtain plane polarised light
1, pg 45 reflection
2. refraction
3. dichroism [ absorption]
4. scattering
5. double refraction
reflectin of plane wave hugen principle
notes pg 47
refraction plane wave hugens principle
pg 48
fresnel disance
ray optics is valid upto this distance
z = a^2/ lemda
