Go Back   Science Forums Biology Forum Molecular Biology Forum Physics Chemistry Forum > General Science Forums > Physics Forum
Register Search Today's Posts Mark Forums Read

Physics Forum Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Confused about how to differentiate between these two equations for energy. Please help.

Confused about how to differentiate between these two equations for energy. Please help. - Physics Forum

Confused about how to differentiate between these two equations for energy. Please help. - Physics Forum. Discuss and ask physics questions, kinematics and other physics problems.


Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 05-18-2004, 01:25 AM
Larry McFarren
Guest
 
Posts: n/a
Default Confused about how to differentiate between these two equations for energy. Please help.



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
radiation would fall into the

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.



Do you see my contradiction. I'm confused here, please help. Thanks.

Reply With Quote
  #2  
Old 05-18-2004, 02:18 PM
N:dlzc D:aol T:com \(dlzc\)
Guest
 
Posts: n/a
Default Confused about how to differentiate between these two equations for energy. Please help.

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


Reply With Quote
Reply

Tags
confused , differentiate , energy , equations


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
New theory time travel and quantum computer reactor1967@yahoo.com Physics Forum 0 04-08-2008 04:29 AM
THE NEW THEORY OF RELATIVITY karamihas@ath.forthnet.gr Physics Forum 2 11-01-2006 03:07 PM
Do Physicists Understand Their Own Peer-Reviewed Literature? Perfectly Innocent Physics Forum 320 11-06-2003 11:01 PM
US weight and measures prior to 1953 Danny Deger Physics Forum 30 07-30-2003 06:35 PM


All times are GMT. The time now is 09:40 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright 2005 - 2012 Molecular Station | All Rights Reserved
Page generated in 0.13094 seconds with 16 queries