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

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

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

x_n=2n

(

)

= n

Condition for darkness :

Path difference = (2n - 1) ,	l	, l = wavelength of light, n = 1, 2, 3,…

	2

Distance of n^th dark band from central bright fringe ( CBF )

x_n = (2n-1)

Band width :
Distance between two consecutive bright bands = Distance between two consecutive dark bands

Band width X =	lD	,

	d

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
d_1: distance between magnified images
d_2: distance between diminished images

d₁ =

d₂ =

u + v = D

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

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