If intensity in YDSE is `50%` of maximum at a point. Calculate the path difference.

Explanation

`I=I_(0)cos ^(2)((phi)/(2))`
`(I_(0))/(2)=I_(0)cos ^(2)((phi)/(2)), phi=(pi)/(2)`
`(2pi)/(lamda)Deltax=(pi)/(2)`
`Deltax=(lamda)/(4)`