Unformatted text preview: bruary 24, 2013 Maxima and Minima Algebra
Assume that the two sources are in
For maxima, we want constructive
r2 - r1 = mλ, with m = 0, ±1, ±2, ...
For minima, we want destructive
r2 - r1 = (m+½)λ, with m = 0, ±1, ±2, ...
There are alternatives - the two
sources could be out of phase.
In this case we obtain minima where
there were maxima, and vice verse.
More generally, there could be any
phase difference between the two
Sunday, February 24, 2013 Radio Stations
Consider a radio or TV station
w ith a single vertical dipole
antenna. It will broadcast its
signal equally in all directions
along the surface.
But if we add a second antenna,
The interference pattern
results in more energy going
o ut in some directions - so the
signal can be received further
away - and less going out in
other directions. Sunday, February 24, 2013 In the conﬁguration shown,
interference reduces the energy
going out in some sideways
directions. If we changed the
antennas to be out of phase,
interference would reduce the
energy going to the left and right. iClicker:
You are going to use two antennas to broadcast radio
mainly east/west from the center of Long Island. The
antennas have to be east/west of each other. Should
they be in phase or out of phase?How many wave
lengths apart should they be? Choose the best answer
e) 0λ in phase.
0λ o ut of phase.
½λ o ut of phase.
½λ in phase.
1λ, phase does not matter. Sunday, February 24, 2013...
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