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S : narrow slit (adjustable)
B : biprism (mounted on a stand, slided along optical bench)
L1, L2 : Convex lenses mounted on stand
E : eyepiece
Interference pattern is obtained when the edge of the biprism becomes
exactly parallel to the slit.
Wavelength of monochromatic light l =
X : band width,
d : distance
D : Distance between sources and screen.
(Measured from scale on optical bench)
of Band Width: Micrometer reading when cross wire is
coincident with any bright band is noted, say x1. Readings
corresponding to consecutive bright bands, x2, x3 … etc. are
noted. Average value of x2 - x1, x3 - x2 etc. gives
average band width X.
DIAGRAM OF BIPRISM EXPERIMENT
S = Real
source (a slit)
S1, S2 = Virtual sources (i.e.,virtual images
of the slit),
B = Biprism, R = Region of interference
Measurement of d
show that d =
Principle: Property of conjugate foci of the
convex lens according to which the positions of object and image can
d = actual
distance between S1 and S2
= size of object
d1 = size of
Size of object
What happens when
In the biprism experiment, if
(a) the eyepiece is moved towards the slit?
(b) the distance between the virtual sources
In the biprism experiment, band width X =
(a) If eyepiece is moved towards slit, D will decrease.
Since X µ D (l, d constant)
\ Band width
(X) will decrease.
(b) If d decreases, since X µ
(l, D constant)
\ Band width (X) will increase.