Electrons have a mass, as a particle with mass, they experience most effects of objects with a mass. So do they experience any sort of wind resistance? Or is that simply explained by their cross section interaction probability with a given particle?
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1$\begingroup$ could you maybe specify the physical situation that you have in mind? For example, electron from cosmic rays traveling in the atmosphere? Electrons in solids? $\endgroup$– sinteticoSep 7, 2020 at 7:55
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$\begingroup$ @sintetico I would mostly be talking about electrons allowed to "freely roam". I.e electrons who would not be confined to the cloud around an atomic nucleus. But perhaps that situation would be insightful in some way as well. $\endgroup$– hisairnessag3Sep 7, 2020 at 14:59
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2$\begingroup$ Wind resistance has nothing to do with mass. $\endgroup$– Norbert SchuchSep 7, 2020 at 15:38
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6 Answers
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If we speak of electrons, then it is appropriate to speak of "wind* as a flow of atoms. Electrons are usually confined to atoms or materials, inside of which the wind atoms do not penetrate, so the collision of electrons with wind are very unlikely.
One place where one does encounter a stream of unbound electrons is electron microscope. In this case one always assures that the measurement takes place in vacuum, since otherwise electrons will indeed get scattered by air.
Finally, in particle colliders streams of particles are routinely scattered against each other. One could think of it as electrons experience resistance of, e.g., a wind of protons.
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3$\begingroup$ In radiation oncology, electron beams sometimes are used to treat skin cancer. The beam exits from the vacuum environment of a linear accelerator through a thin-but-solid metal "window," and it it may have to pass through ten centimeters or more of room air before interacting with the patient's skin. I don't know how or how often the electrons, which have a kinetic energy on the order of several MeV, interact with the air molecules. $\endgroup$ Sep 7, 2020 at 15:25
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$\begingroup$ @SolomonSlow This is very interesting! I imagine one could calculate collision frequency between electrons and the air to see, whether there is an important effect. $\endgroup$– Roger V.Sep 7, 2020 at 15:27
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If one imagines a macroscopic object moving through air, one can very well approximate air resistance as the action of a continuous fluid. At low speeds, this situation can be described by viscous friction, which is a force proportional to the speed of the object, and with direction opposite to its direction of motion (I neglect here the effect of turbulence).
If you have electrons moving in a medium, for example, cosmic rays moving through air, or electrons moving in a solid or in a liquid due to the effect of an electric potential, the above approximations cannot be valid. One cannot approximate the action of the medium on the electron as the action of a continuous entity. From the point of view of an electron, air, fluids, or a solid, are made of individual atoms. Therefore, one has to consider the statistical average of all possible collisions (scattering) of the electron with atoms. The situation is better described as individual collisions, Brown motion in fluids, or Drude theory of solids, depending on the context. All these approaches consider the statistical average of the medium on the electron trajectory. In practice, the electron will move freely for an average distance $l$, which is called the mean free path. Surprisingly, or maybe not, in the Drude theory of electron in solids, the average effect of collisions is proportional to the electron velocity, analogously to the case of viscous friction.
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Electrons do have a mass ($9.10938356 \times 10^{-31}\,\mathrm{kg}$). The effects of this mass in your particular situation are likely immeasurable though.
I partially agree to Vadims answer, collision of electrons with wind are very unlikely indeed.
There is another kind of resistance electrons would experience in this case. The air that typically makes up wind consists of more than just regular oxygen molecules (O2). There will likely be ionized particles, some may even be caused by the aforementioned stream of electrons. Ionized air will interact with electrons and thus provide some kind of resistance.
I wouldn't really consider it wind resistance though.
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I think maybe the most common event in which electrons might encounter 'wind resistance' would be during the initiation of a lightening strike, where leaders ionize a path to ground. That process does not move from point to point at the speed of light, but at the speed with which atoms can be ionized in the general direction of the lowest resistance path. The act of ionizing is accomplished by free electrons produced by the potential difference between cloud and ground. Something else to think about; electrons, like photons move from one atom to the next in a chaotic way that is determined by the availability of a place in the orbit structure of the receiving atom, thus an individual electron moving in a wire may take aeons to go inches, while the effect of the electron being introduced at one end will be measured at the other end at the speed of light.
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A high voltage electric arc between two vertical wires, whose separation increases with height, tends to move up (even though the separation is increasing). I assume this motion is caused by the convection of heated air. (This situation does include ionized atoms.)
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Short answer: NO
Medium answer: The electron will not be slowed or pushed by wind or air, it will either hit a single atom or it won't.
Longer answer:
Wind resistance (drag) deals with objects on a macro scale. It is a simplification dealing with many, many atoms in both a gas and an object moving through the gas. Take for example a .177 steel BB. There are about 3 million million million million atoms. When moving through the air these atoms displace the air in a certain way and this slows the BB down (wind resistance). The wind resistance or drag depends on the item's size and shape because it deals with how the atoms in the BB push the atoms in the air out of the way.
Contrast this with a single electron. The tiny electron is not going to push heavy atoms out of the way to create drag. Instead, the electron will be absorbed if slow enough and create a negative ion, or bounce off the atom. The atom itself has electrons and much heavier protons and neutrons. As a very rough example it would be like that BB hitting a cinder block. The BB is not going to go through a sea of cinder blocks and push them out of the way to create drag. It might knock off a chunk of one cinder block and slow down (like an electron dislodging another electron in the atom to create a positive ion), but it will be bounced off in a different direction at a slower speed.
answered Sep 7, 2020 at 20:40