Insights Blog
-- Browse All Articles --
Physics Articles
Physics Tutorials
Physics Guides
Physics FAQ
Math Articles
Math Tutorials
Math Guides
Math FAQ
Education Articles
Education Guides
Bio/Chem Articles
Technology Guides
Computer Science Tutorials
Forums
Trending
Featured Threads
Log in
Register
What's new
Search
Search
Search titles only
By:
Menu
Log in
Register
Navigation
More options
Contact us
Close Menu
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Forums
Physics
Classical Physics
Optics
Energy of Electromagnetic Waves in Destructive Interference
Reply to thread
Message
[QUOTE="keep_it_simple_silly, post: 6812858, member: 729886"] Hello Martin! Many of the answers say that the conservation of energy is maintained because energy is 'redistributed' or goes to other location of constructive interference. This is an explanation which only roughly fits in certain cases but fails in some other. The real explanation is not as straightforward as it seems. Although the energy of the whole system (source + receiver medium) is conserved, the energy radiated to the medium is not always the same or conserved! In the case of YDSE or Young’s Double Slit Experiment, we observe that the average intensity of the fringes to be 2 times the Intensity of a single source. So far so good, then where’s the problem? Now consider the following situations. Consider 2 sources are radiating waves of same frequency, same amplitude and no phase difference. :- [LIST=1] [*]In case 1, the distance between these sources is λ/2, as shown in Figure 1.[ATTACH type="full" width="321px"]315822[/ATTACH] [*]then it is reduced to 0 in Figure 2. [ATTACH type="full" width="377px"]315823[/ATTACH] [*]If we calculate the power dissipated in these 2 cases, it turns out to be equal to 2*P in case of Figure 1, and 4*P in case of Figure 2. This clearly shows that by changing the distance, the net energy dissipated in medium is changing, not conserved. We can qualitatively see this in Figure 1 and Figure 2. In Figure 1, The waves are absent in the sides, and in Figure 2, waves are present everywhere. This gives us the clear idea that more energy is being spent in case of Figure 2 The question is how? [LIST] [*]In order to give an explanation to this phenomenon, which fits all the cases and doesn't fail at any case, it is necessary to consider the ‘work done' by the source or the ‘wave impedance’. For example, do you think that a source generating a wave of amplitude A in a vacuum and a source generating the same wave in the environment when there is a varying electromagnetic field present at the source requires same amount of energy? [*]This situation can be compared to pushing a rock on a plane surface vs pushing it on a hill. To get the same displacement, more energy needs to be transferred in case of pushing rock on the hill. This is because there is an ‘opposing force’ present in the latter case. [*]In a similar way, when a source is generating a wave of amplitude 𝐴A when there is already a wave of amplitude 𝐴A present at the source, it needs to provide more energy to the system. The additional energy it is providing, in this case, is KA^2. So total energy provided by one source becomes 2KA^2, and when we add the energy from both sources, the net energy becomes 4KA^2. [*]The case of 2 sources of opposite phases present at the same point, can be compared to pushing a rock down the hill. Because of the opposite nature of the field present at the source, the total work done by the source will become 0, and that is why there is no net radiation present, radiation being the transfer of energy to the medium by the source. [*][ATTACH type="full" width="568px"]315824[/ATTACH] [*]The concept of work done by the source was explained using term wave impedance by Levine in 1980 [URL='https://www.tf.uni-kiel.de/matwis/amat/admat_en/articles/interference_paradox_article.pdf']Ref[/URL], it’s explained in [URL='http://aapt.scitation.org/doi/10.1119/1.4895362']ref[/URL] written by Authors Robert Drosd, Leonid Minkin, and Alexander S. Shapovalov [b][Link to personal web blog redacted by the Mentors][/b][*]Hope this helps! thank you! [/LIST] [/LIST] [/QUOTE]
Insert quotes…
Post reply
Forums
Physics
Classical Physics
Optics
Energy of Electromagnetic Waves in Destructive Interference
Back
Top