i have a doubt

what is the formulae to find dark fringe

is it (2n+1)LD/2d

or it is (2n-1)LD/2d

where L is lambda

both are correct but 2n-1 is preferably used

in the formula 2n-1  n is the position of dark fringe

while  for 2n+1 position of fringe is n+1

example n=0 => 2X(0) +1 =1 [1ST DARK FRINGE]

Approved

thnk u

Dear Vijesh

Both the formulae are correct, on putting n as sum integer we get two successive dark fringes by those 2 formulae