In Young's double slit experiment intensity at a point is `((1)/(4))` of the maximum intersity. Angular position of this point is

Explanation

`I=I_(max)cos^(2) ((phi)/(2)), :. (I_(max))/(4) = I_(max) cos^(2) ((phi)/(2))`
`cos ((phi)/(2))=(1)/(2) or (phi)/(2) = (pi)/(3)`
`:. phi =(2pi)/(3)= ((2pi)/(lambda)). Delta x` where `Delta x= d sin theta`
`(lambda)/(3) =d sin theta, sin theta= (lambda)/(3d)' theta= sin^(-1) ((lambda)/(3d))`