Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum Confused about how to differentiate between these two equations for energy. Please help.

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#1
05-18-2004, 01:25 AM
 Larry McFarren Guest Posts: n/a

I'm confused about how these two different formulas for calculating signal
energy. I could really use your help.

1. Using Planck's constant, the energy of an electromagnetic plane wave is
related by:

Energy = (6.625*10^(-34)) * (frequency of the signal)

So, as the frequency is increased, the energy increases as well. Ionizing

high energy realm of physics. Now, my confusion starts.

Does this only hold when looking at the signal as light -> photons?

Why doesn't signal amplitude play into this equation?

2. On the other hand, if I have a rectangular pulse, f(t), representing a high
bit being transmitted through a communication channel, of amplitude A with
period T (or frequency F), the signal energy is given by:

Energy = Integral from 0 to T of f(t)^2 = (A^2)*T = (A^2)/F since T = 1/F

So, in this case, as the frequency increases, the energy decreases. This makes
sense to me. Cell phones with high frequency transceivers use
less energy than their old lower frequency analog counterparts - yielding
longer battery life but can't trasmit a signal as far.

#2
05-18-2004, 02:18 PM
 N:dlzc D:aol T:com \(dlzc\) Guest Posts: n/a

Dear Larry McFarren:

"Larry McFarren" <[Only registered users see links. ]> wrote in message
news:kCdqc.810\$[Only registered users see links. ].prodigy.com. ..
signal
is

The energy equation you cite only considers the energy of one photon. A
more complete formula might be: E = n * h * nu
where n is the number of photons (intensity times area, or just amplitude),
h is Planck's constant, and nu is 2 * pi * frequency.

high
with
makes

Not true for the reasons you suspect. Batteries have gotten a little
better, digital communication has better "carry", antenna design has
improved, receiver design has improved, and idle power is managed better.
They don't need to emit as much power to be "heard".

As to the formula you cite, this is a new one on me... It looks like the
energy of a half a square wave, so as frequency increases, the amount of
energy in any given time frame (independent of frequency or period) is
constant.

David A. Smith

 Tags confused , differentiate , energy , equations

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