MHT-CET : Physics Entrance Exam

### MHT - CET : Physics - Interference of Light Formulae Page 1

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1. Conditions for constructive and destructive interference

1. Condition for brightness:
Path difference =
nl, l = wavelength of light
(
n = 0, 1, 2, 3, …)
Distance of nth bright band from central bright fringe ( CBF )

xn=2n

(

 l 2

 D d

= n

 lD d

1.
2. Condition for darkness :
 Path difference = (2n - 1) , l , l = wavelength of light, n = 1, 2, 3,… 2
1. Distance of nth dark band from central bright fringe ( CBF )

xn = (2n-1)

 lD 2d

1.
2. Band width :
Distance between two consecutive bright bands = Distance between two consecutive dark bands
 Band width X = lD , d
1. l : wavelength of light
D : Distance between screen and source
d : distance between sources

2.Wavelength of light from biprism experiment

 l = Xd D

 = X D

X : band width
d : distance between coherent sources
D : Distance between sources and screen
d1: distance between magnified images
d2: distance between diminished images

d1 =

 vd u

d2 =

 ud v

u + v = D

u : Distance between slit and lens
v: Distance between lens and eyepiece

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