How do we know that a wave of light has electric field? Maxwell proved that light is an electromagnetic wave. Can you give me a reference of an experiment which proves light as an EM wave?
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Light is made of many photons. Billions of individual and coherent photons only resemble a wave but their still individual particles. – Bill Alsept Dec 15 '19 at 05:11
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Take a sheet of glass. Sputter a thin film of silver on one surface of it. Turn it around and look at your reflection in the mirror you just made. That works because silver has high electrical conductivity, so it reflects light just the same as it would reflect RF EM waves. – The Photon Dec 15 '19 at 05:15
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2Look up Hertz experiment – user6760 Dec 15 '19 at 06:36
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This article talks about measuring the effects of the magnetic field of light, which are smaller than the effects of the electric field. – G. Smith Dec 15 '19 at 06:37
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2Maxwell knew because when he computed the velocity of EM waves he got the speed of light. A modern experiment is visible light from synchrotron radiation. – Dec 15 '19 at 09:43
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@The Photon Raw silver also has high electrical conductivity but it don’t reflect light same as a mirror. So reflection have some kind of relation with arrangement of atoms of the surface and may be also with conductive properties. If sunlight falls on a stone and those reflected rays from the stone hits retina of my eyes that doesn’t prove stone as a conductor of electricity or light as an electric field. Anyway, do you know any other experiment where we change frequency of light and it directly affects an electric field detector? – Dec 15 '19 at 14:16
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1@user248881, the surface of raw silver doesn't have high conductivity (and doesn't produce specular reflection), because it oxidizes rapidly when exposed to air. That's why when you sputter it onto glass (protecting it from exposure to air) you see a different kind of reflection than if you just look into the flat surface of a silver butter knife. You can of course make a pure silver mirror (no glass), but you have to keep polishing it to remove the oxide layer. – The Photon Dec 15 '19 at 16:36
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As for the second part of your comment, the problem is that the E field oscillations of visible light are in the 100's of terahertz in frequency. The kind of electric field detectors we use at DC and RF can't respond so quickly. So we use different kinds of detectors, like photodiodes, to detect optical EM waves. Nonetheless everything we observe about light is consistent with it being an EM wave. – The Photon Dec 15 '19 at 16:38
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@user248881 If you can physically explain what a wave of light really is then maybe the question could be answered. A wave of light is made of individual photons. Protons and space is all there is and coherently they resemble waves and fields. – Bill Alsept Dec 16 '19 at 01:24
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@Bill Alsept A wave of light carries energy with it and as you may know the particle that carries that energy is known as photons. But it has no charge, so the question arises in my mind is, how can wave of light has electric field? And if it has then, isn’t there a single experiment which detects electric field around light? – Dec 16 '19 at 01:37
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@user248881 Considering the so-called wave is a billion coherent photons radiating outward from a common source your answer will be found with the individual photons. Each one of those photons has a frequency. What are they frequently doing? Look at page 7 of my paper. Billalsept.com – Bill Alsept Dec 16 '19 at 01:43
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@Bill Alsept Photons are vibrating or fluctuating? – Dec 16 '19 at 01:49
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@user248881 everything points that and it’s easy to derive any phenomena based on that. – Bill Alsept Dec 16 '19 at 02:02
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@The Photon I can see my face on a plastic CD case, even though plastic is not a good conductor of electricity. And don’t we measure electric field in volts/meter instead hertz? Photodiode uses energy that are within the photons to generate electric current. So it’s called energy conversion. That doesn’t mean light carries electric field. – Dec 17 '19 at 04:45
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1@user248881, If there was one definitive experiment to prove that light is EM waves, somebody probably would have mentioned it by now. All I can say is that all the experiments we do are consistent with light being EM waves (including reflection from dielectric boundaries like that CD case), and none show light to be something other than an EM wave, so the physics community is quite convinced that light is a form of EM wave. – The Photon Dec 17 '19 at 05:42
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The development is actually the other way around. We knew about light first, and only later discovered radio waves and demonstrated their similarities to light.
Obviously, we were aware of light (at least in a general way) since pre-historic time since we could see things, it was easier to see things at night if we lit a fire, etc. Later we knew we could separate light into its component colors using a prism, etc. By the 18th century we had measured the speed of light to a reasonable degree of accuracy.
But we didn't know the underlying nature of light. Both wave and particle ("corpuscular") theories of light were proposed.
In 1861 James Clerk Maxwell theoretically developed his well-known equations describing electromagnetic wave behavior. This theory predicted that electric field disturbances would propagate at the same speed as light. This theory suggested that light and electromagnetism were the same phenomenon but hadn't been experimentally proven yet.
In 1887, Heinrich Hertz performed a series of experiments to test the hypothesis that electromagnetic waves could be produced and would propagate like light. In one example, he used a spark gap to generate a disturbance of the electromagnetic field, and showed that this could be received by what we'd now call a loop antenna at some distance away from the transmitter. Hertz was also able to generate standing waves by reflecting a transmitted signal off of a sheet of metal, and from the observed standing wave pattern show that the speed of the electromagnetic wave was the same as the speed of light.
Since then, continued experimental results have all been consistent with the conclusion that light and electromagnetism are one and the same phenomenon, and none have shown any inconsistency in this theory.
In comments you mentioned,
the particle that carries that energy is known as photons. But it has no charge, so the question arises in my mind is, how can wave of light has electric field?
The charge is the source of electromagnetic waves. That doesn't mean that electromagnetic waves must carry charge. The electromagnetic wave (or the photon) is the mechanism by which a charge in one location can affect the behavior of a charge some distance away. But it doesn't have to carry the charge over to the other place and whack the 2nd charge with the first one to do that.
The Photon
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