Thu June 09, 2011 By: Devesh Saxena

Find the number of bright fringes formed over the 120mm distance.

Expert Reply
Mon June 13, 2011
In the case of varible thickness,
Fringe width = lamda/ 2mu theta = y/l
Let N be the number of fringes formed over length l,
l = N beta 
N = 2mu l tbeta/lamda
N = 2X 1X0.048X10^-3/(680X 10^-9) = 141
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