DIFFRACTION-:
1)it occurs due to superpos. of secendary wavelets frm exposed part of a coharent source
2)inte3nsity of succesive bright fringes goes on dec.
3)intensity of dark fringes is never zero
4)diff. fringes are never of = width
5)conditions for max. are
a)path diff. delta.x= (2n+1)lamda/2
b)phase diff. = (2n+1)lamda/2
c)time diff. = (2n+1)T/2
6)conditions for minima are
a) path diff. = n*lamda
b)phase diff.= 2n*pi
c)time diff. =nT