1. Two source interference
constructive interference
destructive interference

2. Two source interference
Path difference =
S2P
– S1P
= 1 wavelength
=  P
constructive interference
destructive interference S1 S2

3. Two source interference
Path difference for constructive interference =
n 
(where n is an integer) 
2  3
constructive interference
destructive interference

4. Two source interference
Path difference for destructive interference =
(n + ½) 
(where n is an integer) ½
1½ 
2½ 
constructive interference
destructive interference
Free powerpoints at

5. Two source interference
The path difference is
n for constructive interference
(n + ½)  for destructive interference

6. This powerpoint was kindly donated to www.worldofteaching.com
is home to over a thousand powerpoints submitted by teachers. This is a completely free site and requires no registration. Please visit and I hope it will help in your teaching.