In a double slit experiment , the coherent sources are spaced 2d apart and the screen is placed a distance D from the slits. If `n^("th")` bright fringe is formed on the screen exactly opposite to a slit , the value of n must be -

Options

A. `(d^(2))/(2lambdaD)`
B. `(2d^(2))/(lambdaD)`
C. `(d^(2))/(lambdaD)`
D. `(d^(2))/(4lambdaD)`

Answer

B

Explanation

the fringe width in this case is `(lambdaD)/(2d)` and the `n^(th)` bright fringe is formed at a distance d away from the centre.
Therefore, `d=n(lambdaD)/(2d)` giving the value of n.