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In Fresnel bi prism experiment if prism angle $\alpha=1^{\circ}, \mu=1.54$ distance between prism and sources a is $0.3\;m$ and wave length $ \lambda= 180 \pi \;nm$ find the fringe width, distance between screen and prism $b= 0.7 \;m$

$(a)\;10^{-4}\;m \\ (b)\;10^{-3}\;mm \\ (c)\;10^{-4}\;mm \\ (d)\;10^{-3}\;m$

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1 Answer

Fringe width $\beta=\large \frac{(a+b) \lambda}{2a(\mu-1) \alpha}$
($\alpha$ in radius)
$\qquad= \large\frac{(0.3 +0. 7) 180 \pi \times10^{-9}}{2 \times 0.3 (1.54 -1) (1 \times \large\frac{\pi}{180})}$
$\qquad= 10^{-4} m$
Hence a is the correct answer.
answered Jan 21, 2014 by meena.p

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