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Unformatted text preview: ’  ``peaks’’ and ``valleys’’ are
emitted at the same time from each source.
The waves are also ``in phase’’ at points a and b, but not at point c.
The distance to a or b is an even number of wavelengths different.
The distance to point c is not.
Sunday, February 24, 2013 Maxima and Minima At some places the waves add up and you get constructive
interference and maxima  for  E ﬁelds, the sum is (E1+E2)cos(ωt).
At other places the waves add up ``out of phase’’ and you get
destructive interference and minima  if the E ﬁelds are , the sum is
always 0!
And at most places you are somewhere in between these limits.
Sunday, February 24, 2013 Let's see a demo and a simulation of 2source wave interference.
iClicker
I am going to move the sources apart. Will the
minima / maxima lines move?
a) No! Of course not.
b) Yes! The angles between them increase and you
get fewer of them.
c) Yes! The angles between them decrease and you
get more of them.
d) Yes! You get more minima lines but fewer maxima
lines.
e) Yes! You get more maxima lines but fewer minima
lines.
Sunday, February 24, 2013 iClicker:
I am going to shift the wave frequency from red to
blue. (Make the wave length shorter.) What happens
to the angles of the minima lines?
a) They stay the same. Nothing changes.
b) The angles decrease  the lines move in and there
are more of them.
c) The angles increase ...
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This document was uploaded on 02/18/2014 for the course PHYS 228 at Rutgers.
 Spring '12
 RonGilman
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