There's this theory that electromagnetic waves can't make through holes that are smaller than their wavelength its supposed to be how microwaves stop microwave radiation from coming out... But that doesn't make sense. I mean it would make sense if the theory said that em waves couldn't make through holes smaller than the amplitude of the wave but I just don't get how the wavelength affects the passing of the wave through holes. So can anyone explain this to me. It would be great if you could explain it to me using funder mental electromagnetic equations or maxwells equations but Anything would be helpful... Thanx in advance
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asked Sep 25, 2020 at 13:36
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1$\begingroup$ EM wave amplitudes do not have dimensions of length, so it does not make sense to compare them to the size of holes. $\endgroup$– SandejoCommented Sep 25, 2020 at 16:24
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2$\begingroup$ Does this answer your question? Diffraction by small holes $\endgroup$– asd.123Commented Sep 30, 2020 at 21:01
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3 Answers
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For an electromagnetic wave approaching to a hole with diameter d, the oscillations with a certain frequency repels and attracts electrons in the material, then moving electrons will create electromagnetic waves. So, some of the wave is blocked by electrons wave which are induced by initial wave.
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$\begingroup$ I just read somewhere that this holds true even for mechanical waves and if so, it has little to do with inducing oscillations in the material. $\endgroup$– DKNguyenCommented Sep 25, 2020 at 13:51
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$\begingroup$ @DKNguyen could you give a link of where you read. It is similar in mechanical waves and when wave oscillate the material then the boundary if the whole also oscillate so the cancellation is similar. $\endgroup$– asd.123Commented Sep 25, 2020 at 13:53
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$\begingroup$ Are you saying that if the material was perfectly stiff a mechanical wave would be able to pass through largely unimpeded? This is one place I saw it: quora.com/… $\endgroup$– DKNguyenCommented Sep 25, 2020 at 13:54
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$\begingroup$ @DKNguyen actually electrostatic laws requires the induction and for the mechanical wave I think it is directly related by the material property where the wave (I mean the medium)and the boundary collision will determine by it. $\endgroup$– asd.123Commented Sep 25, 2020 at 14:10
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I'm no expert, I don't even have a clear answer. It certainly does not make sense if you think about it as a rod of a certain length trying to slip lengthwise through a hole of a certain diameter. Instead, try thinking about it the wave inducing oscillations in the charges around the hole the material is in and those charges oscillating in the material produce new EM wave on the other side of the material that continue on.
However, I just read that apparently this phenomena holds true even for non-electromagnetic waves. It was explained as being due to the interference pattern formed. If this is indeed the case, then it has nothing to do with inducing oscillating charges in the material.
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When an Electromagnetic wave goes through a hole or a grid, it propagates new waves and you have superposition of the new waves. The size of the hole or the grid only affects how the new waves will look like and at what degree they will be diffracted.
What actually stops Electromagnetic waves is the material. Every material can absorb, reflect and transmit different wave-lengths. A simple example is a mirror, it will reflect all visible light wavelengths. If you hold a piece of red-stained glass in front of your eyes it will only allow red-light wavelength to go through, this is why you see everything redish. The absorption and reflection phenomena are explained with quantum mechanical oscillations of the electrons.
