Example
Hence first diffraction minimum occurs just before the bright fringe with m=5
central diffraction peak contains m=0, ?1, ?2, ?3, ?4 => nine fringes
(b) how many bright fringes are within the first side peaks of the diffraction envelope?
Outer limit of first side diffraction peaks are the second diffraction minima : a sin?=2?
substitute for sin?= 2?/a in d sin?=m? ==> m=2d/a = 9.6
hence m=5,6,7,8,9 lie within the peak => 5 fringes