Interference of Light at a Double Slit

Condition for a maximum:

d sin a = k l

d ... spacing between slits
a ... angle
k ... order of the maximum (0, 1, 2, ...)
l ... wavelength

Condition for a minimum:

d sin a = (k + ½) l

d ... spacing between slits
a ... angle
k ... order of the minimum (0, 1, 2, ...)
l ... wavelength