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interference question



I can't really follow with your argument, while qualittaively I understood
what your meant totally.
The average intensity is 2a^2, but for individual wave, the average
intensity is only (a^2)/2 (averaging cos^2 for each), and hence the total
average intensity of the two waves is a^2.
Can you pls show me step-by-step how you arrive at the conclusion that
energy is conserved. thanks

romanza

----- Original Message -----
From: Michael Moloney <moloney@NEXTWORK.ROSE-HULMAN.EDU>
To: <PHYS-L@lists.nau.edu>
Sent: Saturday, September 11, 1999 8:43 AM
Subject: interference question


The point of constructive interference has intensity 4A^2. But you can
find another spot
where the intensity is zero. Does energy conversion hold up? Yes it
does, and one nice
way to see it is in the distant interference pattern of two very narrow
slits.

Very far from the slits along their perpendicular bisector the intensity
is 4A^2. At other
angles very far from the slits (assuming equal amplitudes A due to each
slit) the intensity
depends on the cosine squared of half the phase difference between the
waves. You find
out that the average intensity is 2A^2 when all is said and done, just
like you expect from
energy conservation.

Mike


Mike Moloney, Dept of Physics & Applied Optics, Rose-Hulman Institute of
Technology

(812) 877 8302 http://www.rose-hulman.edu/~moloney