$1.$ In Young$$s double slit experiment IO is the maximum intensity and $\backslash$beta is the fringe width. if $\backslash$delta is the phase difference between the interfering beams at any point P at a distance y from the central band then a$.$ I at P is equal to IOcos$2\backslash$delta $2$ b$.$ I at P is equal to IOcos$2\backslash$delta c$.$ I at P is equal to IOcos$2\backslash$pi y $\backslash$beta d$.$ if Y$=0\mathrm{.}25$ mm$,\backslash$beta $=1$ mm then intensity at P is equal to I$0/4.$