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Q: Where would the energy go when cancelling waves in vacuum? ( Answered 2 out of 5 stars,   9 Comments )
Question  
Subject: Where would the energy go when cancelling waves in vacuum?
Category: Science > Physics
Asked by: juliaann-ga
List Price: $5.00
Posted: 03 Oct 2006 08:53 PDT
Expires: 02 Nov 2006 07:53 PST
Question ID: 770451
If two EM waves 180 deg. out-of-phase meet in a vacuum they would cancel out. 
1. Where would the energy go?
2. How would you explain the result using photons?

Take a look here before answer:
http://www.advancedphysics.org/forum/showthread.php?t=2459

Clarification of Question by juliaann-ga on 06 Oct 2006 08:45 PDT
I think I got one or two better comments in the free "yahoo answers":

http://answers.yahoo.com/question/index;_ylt=Aid5Gz_DqYURPaIHjEi3vDnsy6IX?qid=20061003092855AAW14qJ
Answer  
Subject: Re: Where would the energy go when cancelling waves in vacuum?
Answered By: hedgie-ga on 06 Oct 2006 21:56 PDT
Rated:2 out of 5 stars
 
Are you conducting a poll?

This is a FAQ question, which was discussed at length in the physics
usenet group and was already answered here on GA:

http://answers.google.com/answers/threadview?id=486786

There really is no mystery here. It is like asking:

I keep pouring water into a bucket. When the bucket gets full, where does
the water go?

The point is: you cannot keep pouring water into a full bucket.
 No energy flows into the space in which the two waves are cancelling each other
(after the initial transient).


Hedgie

Request for Answer Clarification by juliaann-ga on 09 Oct 2006 07:04 PDT
Did you aswer my cuestion with a link to a bad rated answer made by
you and a metaphor?

Did you do that to get less than 4 dollars or are you the
this-aswer-has-not-to-be-aswered-man that insist?

Clarification of Answer by hedgie-ga on 10 Oct 2006 00:54 PDT
Julia
The fact that answer was bad-rated does not mean that it is wrong.

Answer is: After the empty space between the emitters fill up, 
           no more energy flows into that space.

 If you do not understand that, you can ask for clarification.
 You can also ask for refund.

 Your choice.

Hedgie

Request for Answer Clarification by juliaann-ga on 10 Oct 2006 04:22 PDT
I originally said 'Take a look here before answer:' and I gave you two
links with better answers than yours to specifically avoid that sort
of answer.

Think about two laser beam 180 deg. out-of-phase (could be made with
only one divided, changed of phase and redirected with cristals and
mirrows) that are carring energy that get together in some place.
(this place could be all the way in oposit directions or same
directions starting in a cristal or only a dot where you have a wall)

Can you give me a better answer that given in the links or your
respons is (like deepertime said) 'similar in scope and depth to
others I have received
of a similar nature' one more time?

Clarification of Answer by hedgie-ga on 11 Oct 2006 00:02 PDT
Julia - Ann 

I did
'Take a look here before answer:'

and consider those 'answers' (like photons bounce off each other) illiterate.

You say:

Your respons  [sic] is (like deepertime said) 'similar in scope and depth to
others I have received of a similar nature' one more time?


 My answer is  similar to that quoted on Yahoo as given by R. Feynman.
 I do not consider that a problem, actually I was pleased by that. 

 I have  problem understading your RFC:  You want me repeat the correct
 answer once more (perhaps in more simple English?)  or you want a different
 - but still correct answer?  

Hedgie

Request for Answer Clarification by juliaann-ga on 11 Oct 2006 05:28 PDT
Sorry my english
I would like to get some reliable information linked or cited for this
question, not your opinion.
Regards

Clarification of Answer by hedgie-ga on 11 Oct 2006 20:59 PDT
OK Julia,

 Here are few links.  It would help me a lot if you would reveal on what
level you want the explanation to be. You need to understand that I
have no idea how old you are, (what grade of school you finsihed) and
how much math you know or want to use. I will use be conceptual rather
that mathematical explanation
- either way, these are not opinions - rather consequences of the wave equation.

First concept to understand is that of

Search Term: Standing waves 

 (You type the 'search term string (or part of it) into a search
engine to get more info)

 One link you get 

http://www.walter-fendt.de/ph11e/stlwaves.htm

Which shows the standing waves. (You need a browser with Java to see that):


 You are asking about form 1 ( both ends open) . This is shown on acoustical waves
(but concept is same for emg waves as well; By emg I mean ElectroMaGnetic field.

http://en.wikipedia.org/wiki/Electromagnetic_field


Also: 
http://www.sciencenewsforkids.org/.../ Feature1.asp

http://www.stat.uiuc.edu/~ombao/eeg.html


You want to know how much energy is carried by the wave:

Search term: Electromagnetic energy, the Poynting vector

http://www.its.bldrdoc.gov/fs-1037/dir-028/_4090.htm

http://www.glenbrook.k12.il.us/gbssci/phys/CLass/waves/u10l2c.html

more exactly:
http://www.shef.ac.uk/physics/teaching/phy205/lecture_19.htm


To understand the answer, you need to understand difference betwee the
Transient and Steady-state
http://www.engin.brown.edu/courses/en4/notes/Vibesols/Vibesols.html
http://hypertextbook.com/chaos/41.shtml

With these basic concept digested, you can see that

1) When you start the experiment (switch on the emiters) the vacuum
(or ideal medium), originally empty will gradually fill with radiation
(energy flows into the system).

2) Eventually a steady state is established. Medium is filled with standing wave
with a node in the center (as in the applet above)

At that moment no more energy flows into that space.

That is apparent from the symmetry of the experiment, but it can also
be mathematically derived from the wave equations.

Hedgie

Clarification of Answer by hedgie-ga on 12 Oct 2006 00:07 PDT
One more link (I said it is a FAQ) if you need authority rather then understanding:


Energy and interference
Q:, When two light waves cancel each other out, where does the energy
go? ... by some constructive interference someplace else, where the
total energy is ...

http://van.physics.uiuc.edu/qa/listing.php?id=1891


    Note that UIUC.edu  is one of most the prestigious universities in USA
 (MIT class) 
Answers are provided by the  physics department
http://www.physics.uiuc.edu/

Request for Answer Clarification by juliaann-ga on 13 Oct 2006 01:56 PDT
PhD (31)

Are you giving me a lot of general information and 'one' link to
another response similar in scope and depth to the most?

Next 5 dollars in a beer.

Clarification of Answer by hedgie-ga on 14 Oct 2006 23:32 PDT
I am sorry Julia,

    but I really do not understand the above RFC .

  I gave you ' one link with equivalent answer '. 

  
 Are you implying that you would like more than one such link?
 Or that you want more in-depth explanation?

    what does ' $5 in the beer? ' means  ?

Hedgie
juliaann-ga rated this answer:2 out of 5 stars
Thank you for the link to Deeptimer question. The response was similar
in scope and depth to others I have received
of a similar nature. In other words: one FAQ question and one more FAQ
in answer. But some links are good. Thank you.

Comments  
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: probonopublico-ga on 03 Oct 2006 09:29 PDT
 
It would be dissipated as heat.

What else?
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: juliaann-ga on 03 Oct 2006 09:45 PDT
 
I said 'in a vacuum' to specifically avoid that sort of answer.

More information here:
http://www.advancedphysics.org/forum/showthread.php?t=2459
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: probonopublico-ga on 03 Oct 2006 10:57 PDT
 
Radio valves (or tubes in Americanese) used vacuums. did they not?

And did they not get hot?

QED
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: stanmartin1952-ga on 03 Oct 2006 16:37 PDT
 
I think you get a cancellation mathematically, but the energy
continues on with each wave.
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: denco-ga on 03 Oct 2006 17:35 PDT
 
The event happening in a vacuum does not avoid the process of heat
dissipation.
http://helios.gsfc.nasa.gov/qa_sp_ht.html

"There are three ways of transferring heat: convective, diffusive, and
radiative.
...
Radiative transfer uses photons (light or infrared photons) to transfer
heat."
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: redbelly98-ga on 05 Oct 2006 06:55 PDT
 
In the real world, you can't combine two light beams so that they
cancel (180 phase difference) everywhere.  There will always be
constructive interference (no phase difference) **somewhere** in
space, and that is where the energy is.
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: probonopublico-ga on 05 Oct 2006 07:27 PDT
 
Brilliant, redbelly98-ga!

You have just solved the world's energy crisis.

Now, how we can grab ourselves a monopoly?

Just you and me, mate, let's be utterly selfish.

Bryan
Counting the money already
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: kemlo-ga on 05 Oct 2006 09:54 PDT
 
Stop showing off Bryan,

We can't all be as intelegent as you.
Subject: Re: Where would the energy go when cancelling waves in vacuum?
From: juliaann-ga on 13 Oct 2006 02:47 PDT
 
Take a look at deeptimer question:
http://answers.google.com/answers/threadview?id=486786

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