In Young's double slit experiment, the length of band is 1 mm. The fringe width is 0 .021mm. The number of fringes is

The number of fringes on either side of center C of the screen is n1= distance  fringe width =ACβ=0⋅50⋅021≈23 Total number of fringes  =2n1+ central bright fringe  =2×23+1=47 SHORT CUT  Y = N β