Homework

Have a look at these pages:

http://www.physicsclassroom.com/Class/light/u12l1a.cfm

http://www.physicsclassroom.com/Class/light/u12l1b.cfm

The expressions are treated in a somewhat complicated fashion (in the section mentioned below).  If you can, try to find an equation for diffraction.  Something that is easier to make sense of.

If you have time, check out Lesson 3 (at the bottom):

http://www.physicsclassroom.com/Class/light/