Why the light as an electromagnetic wave does not interact with electrical and magnetic fields, while other electromagnetic waves such as radio waves do? For example, radio waves are interfered by EM Fields created by power lines but on the other hand light is not affected by power lines.
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$\begingroup$ they are not at the same frequency. Light is above 100THz whereas radio waves you are refering to are probably about a few kHz, frequencies that may be reached in electrical circuits which would radiate EM waves themselves. Interference is a phenomenon that arise with waves of the same frequency. $\endgroup$– Ronan Tarik DrevonCommented Aug 28, 2017 at 15:48
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1$\begingroup$ Frequency is not the cause because in similar way radio waves of mhz range are affected by power lines of 50-60 hz. $\endgroup$– FarhadCommented Aug 28, 2017 at 16:00
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1$\begingroup$ You keep saying thing like "radio waves of mhz range are affected by power lines of 50-60 hz" and that simply isn't true. Radios can be affected by power-line interference, but the waves have exactly the same superposition behavior as light. $\endgroup$– dmckee --- ex-moderator kittenCommented Aug 28, 2017 at 17:01
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$\begingroup$ I believe to remember that interference is a mechanism that only work for coherent and monochromatic frequencies. Indeed the electrical circuits inside the "radio device" maybe affected by 50Hz EM. $\endgroup$– Ronan Tarik DrevonCommented Aug 29, 2017 at 12:34
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4 Answers
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The e-m fields created by power lines don't affect the passage of e-m waves through the region around the power lines. [Technically a 'principle of superposition' operates, one of whose consequences is that beyond the region of the power lines, you couldn't tell that the e-m waves had passed through that region.] The interference you ask about is what you find when using a radio etc in the region of the power lines. The radio detects the fields due to the power lines and due to the e-m waves. What you hear may therefore not be what you want!
Why we say that light is not affected is because your eye does not respond to the frequencies of the fields from the power line. Your radio set does. Neither light nor radio wave themselves are affected in the way they travel by the fields from the power lines.
answered Aug 28, 2017 at 15:49
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$\begingroup$ Any way the noise in what we listen from radio means that the radio wave is affected by power line EM. $\endgroup$– FarhadCommented Aug 28, 2017 at 16:01
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1$\begingroup$ My point is that it isn't the wave itself that's affected. $\endgroup$ Commented Aug 28, 2017 at 16:08
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$\begingroup$ I've added a bit to my answer to try and make this clearer. $\endgroup$ Commented Aug 28, 2017 at 16:18
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First, note that interference and interaction are two very different things. I'm assuming based on the language of your question you're talking about the interactions between fields, and are using the word "interfere" as in "mess with".
Under that assumption, you are mistaken. Power lines do not create EM fields which interact with radio waves, they create radio waves of their own which are picked up by your receiver.
Random "noise" in the lines causes them to emit electromagnetic radiation consisting of radio waves with rapidly fluctuating amplitudes. As it happens, this is precisely how AM (amplitude-modulated) radio works, so this signal overrides the broadcast signal and your radio goes crazy until you're out of range of the power lines.
FM (frequency-modulated) radio works differently, so you won't notice this effect (at least, it won't be nearly so dramatic) if you're listening to an FM station.
The reason you don't see the radiation emitted by the power lines is simply because the frequency is far too low - but besides that, it's the same stuff as light.
Two disclaimers. First, if the waves are traveling in a medium (such as air), electromagnetic waves can interact with each other indirectly by changing the properties of the medium. For situations like the one you describe, however, this effect is negligible.
Second, at ludicrously high intensities, it is possible to have nonlinear interaction between electric and magnetic fields even in vacuum, but that is the domain of quantum field theory and is presumably not within the scope of this question.
answered Aug 28, 2017 at 15:48
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$\begingroup$ Difference in frequency is not a cause for explaining the interaction between the fields. Example is in AC motors when oscillating and rotating AC magnetic field interacts with DC magnetic fields. $\endgroup$– FarhadCommented Aug 28, 2017 at 16:10
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$\begingroup$ While interaction is a general term and interference has specific meaning in radio engineering, both shows the mutual effects of two components of fields. If oscillating fields with close frequency we will have interference. But any way they interact to each other ! $\endgroup$– FarhadCommented Aug 28, 2017 at 16:13
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2$\begingroup$ Not true. AC magnetic fields do not interact with DC magnetic fields - the total field is just the linear superposition of the two. $\endgroup$ Commented Aug 28, 2017 at 16:19
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Light waves or rays interact with electric fields of electrons in a solar cell to produce a disturbance in electrons so that electricity is produced. In a tungsten bulb, electrons try to move with very close distance because of a voltage, and at the same time the electric fields of these electrons repel them. So, light energy is released. Light energy is associated only with electric fields. (Reference: Planets and electromagnetic waves) Moving electrons have magnetic fields. Radio waves interact with magnetic fields of moving electrons, and disturb the moving electrons to make variations in current. Radio waves are associated only with magnetic fields
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For the specific case of visible light vs. radio waves, the reason they do not interfere is that they are very different wavelengths. Optical receptors are too small to be affected by radio waves and radio antennas are too large to be affected by visible light.
In general, EM waves of a particular wavelength only interact strongly with structures of a similar size. That is why radio waves, with wavelengths of many meters, go through most walls while visible light, with wavelengths in nanometers, do not. There are exceptions of course.
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1$\begingroup$ But please notice that while radio waves go easily through walls they can not go so easily through conducting materials like sheets of metals. And refer to main question we should compare the effects of power line on radio waves in one hand and on light in the other hand. Power lines affect the radio waves while does not affect the light ! $\endgroup$– FarhadCommented Aug 28, 2017 at 16:05