Why is there a negative sign in optical path difference?

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
2 replies · 3K views
moatasim23
Messages
77
Reaction score
0
SOme one help me with the OPD.
How is here the OPD=n2(AB + BC) -n1(AD)?
I am not confused with the introduction of 'n'..Rather the path length is confusing me..Why is there a negative sign?
 

Attachments

  • Path Difference.png
    Path Difference.png
    5.8 KB · Views: 1,404

Discussion

Physics news on Phys.org
They are computing a path difference ...
 
Just to elaborate a little on Simon's response.

Notice that the line connecting C and D is perpendicular to the rays. This indicates the C and D lie on the same wavefront.

Ergo, the OPD is calculated as the difference in optical path lengths from A-C and from A-D.

Claude.