On Mar 30, 11:35 pm, Cecil Moore wrote:
Keith Dysart wrote:
More curiousity: Can P1 and P2 have different signs, that is,
the power is going in different directions?

Please reference Chapter 9, Interference, in "Optics",
by Hecht, 4th edition. The two interfering waves are
traveling in the same direction. The associated
powers exist together at a point of interference.

This is getting way too confusing. After adding absolute value
to clarify which of two possible roots is being used (though
without any rigorous rationale), it turns out that different
formulae are needed depending on the direction.

So some times
Ptot = Pf - Pr
while at other times
Ptot = P1 + P2 + Pfudge

Are there other conditions we need to be aware of when computing
Ptot?

How does this align with your previous quote?
"Known as the *Principle of Superposition*, this property
suggests that the resultant disturbance at any point in a
medium is the algebraic sum of the separate constituent
waves."

Neither of the equations is the "algebraic sum".

....Keith

How does this align with your