11 ms·
I think more than half the time I spent earning my EE degree has been spent unlearning the intuitive (but wrong) things that I was liberally taught. I was fortu
by notalaser 10y ago
I think more than half the time I spent earning my EE degree has been spent unlearning the intuitive (but wrong) things that I was liberally taught. I was fortunate enough to have an exceptional Physics teacher in high school, who managed to avoid a lot of the bullshit that less fortunate students were fed; sadly, I compensated that with some of my own (misguided) self-study.
This experience also taught me to actively mistrust "intuition" and "common sense". Not that there isn't value in intuition (quite the contrary, it's priceless, from design to maintenance), but it's only useful when it rests on a solid theoretical foundation. Prior to earning that foundation, it's nothing but a (very bad) shortcut that people take because they want to feel knowledgeable, but don't want to invest the effort of going through all that math mumbo jumbo.
- k__ 10y agoI got it taught about 3 or 4 times, and every time I understood it less. In middle school they told me, it's electrons moving at the speed of light through a conductor. In high school they told me, no no, they don't move at the speed of light, just when one electron enters the conductor, another one on the other side will leave the conductor, like with peas in a straw. And this enter/leaf is at the speed of light. At university they told me, no no, you got it all wrong, it's about the electro static and electro dynamic fields which stand orthogonal on each other and produce electro magnetic waves... what?! I seriously have no idea anymore.
- selimthegrim 10y agoWell someone fucked you up because current is defined as the flow of positive charges just like the electric field direction is defined as the action of a positive test charge. Thanks Ben (Franklin)
- k__ 10y agolol, seems to be. I read a few articles on that page and it's like magic, it makes not much sens to me after all I learned at school.
- agumonkey 10y agoI start to think that the less you make sense of a topic, the closer you are from real understanding. ps: this comes from years of self learning music, every now and then my incomplete abilities go through a complete crash, only to reveal a critical misunderstanding, lack of sensitivity in my perception or action, that leads to a sudden and very blissful resolution (your own private eureka moment)
- imtringued 10y agoThe first chapter explained it well. There are three different concepts that were all thrown under the umbrella term "electricity". >..little use by educators of the wind/sound electrical analogy: >AIR is a physical substance. >SOUND is a wave that propagates rapidly through a volume of air. >WIND is a flowing motion of air already present. >ELECTRIC CHARGES are a physical substance. >ELECTRIC ENERGY is a wave that travels via a column of charge. >ELECTRIC CURRENT is a flowing motion of the charge already present.
- ZenoArrow 10y ago> ">ELECTRIC ENERGY is a wave that travels via a column of charge." I'm not an expert when it comes to electricity, so someone correct me if I'm wrong, but one thing that has made sense to me when it comes to trying to understand electricity is that not all electrons have equal potential for work. When studying electricity, you're often told the charge of an electron as a fixed quantity. However, if I've understood correctly, the work that an electron can do in conducting electric energy is not wholly described by the charge of the electron, it's also important to know the relationship that the electron has with the nucleus of the atom it orbits (i.e. the 'shelf' it's on). To explain in another way, this analogy may be 'wrong' but I think it helps to think of electrons as capable of more work when they are less tightly coupled from the nucleus of an atom. The electrons that can do the most work are those in the outermost orbit of an atom. Whilst it may be wrong to say outer electrons are more charged than inner electrons, I think it might help in terms of visualisation. Again, correct me if I'm wrong.
- agumonkey 10y agoHow significant is this when you work at the level of Coulombs (high count of charges) ?
- ZenoArrow 10y agoSorry, I don't think I fully understand your question. Again, what I say could be wrong, but if there's a flow of charge it could mean the outer electrons have more charge than they can contain whilst remaining part of an atom, resulting in either electrons breaking free of atoms, or the energy being passed on to another atom (causing a chain reaction as each atom does the same). I'd suggest a higher count of charges just means this is happening more. I think another useful mechanism to consider is that atoms want to return to an electrically neutral state. If they have energy that differs from this neutral state, they will either give out energy or take in energy to reach the neutral state. The movement involved in rebalancing the atoms can be thought of as electric current. Again, happy to be corrected if I'm wrong.
- notalaser 10y agoAs far as circuits go, this is about the closest high school Physics gets to truth (and it's decently close, compared to how wrong it gets e.g. capacitors): > In high school they told me, no no, they don't move at the speed of light, just when one electron enters the conductor, another one on the other side will leave the conductor, like with peas in a straw. And this enter/leaf is at the speed of light. although "entering" and "exiting" the conductor isn't really a good description. A better way to think about it is that "conductor" is really just slang for "material that has a bunch of free electrons and very little room for more". This is the "sea of electrons" that Beaty talks about. It makes sense that, if all this sea flows steadily (i.e. at the same rate throughout the conductor), forcing a change in the rate of flow in one part of the conductor will be felt almost immediately in another part of the conductor, no matter how distant, even if the flow itself is extremely slow. (If you're thinking that this is only true if the "pipe" through which the "sea" flows is full, you're right, this is how free electrons behave in conductors; that's why Beaty insists that a good analogy for a conductor is "like a pipe which is already full of water". > At university they told me, no no, you got it all wrong, it's about the electro static and electro dynamic fields which stand orthogonal on each other and produce electro magnetic waves... what?! If they taught you that, they are most definitely wrong, it sounds loosely like induction, but with two strange names instead of "electric" and "magnetic" :-). This is a better description of the physical reality, and it does help you understand circuits better if you think about it, but not in a very practical manner.
- fzzzy 10y ago> If they taught you that, they are most definitely wrong, it sounds loosely like induction, but with two strange names instead of "electric" and "magnetic" :-). I don't think "definitely wrong" is a good description. electrostatic and electrodynamic are perfectly good, if somewhat archaic, terms for the electric and magnetic fields. (E and H fields)
- k__ 10y agoI probably just translated them wrong from German. But as I said, since I didn't understand it, I probably don't recall correctly what they told me. I just remember that the "particles" I had in mind somehow stopped being "the thing" and now it was all abount strange fields that worked without a physical medium and formed waves by being aligned in a specific way.
- marcosdumay 10y agoYour last two answer are the same. It's just that the last one is much easier to calculate.
- wbeaty 10y agoIt actually is the electrons. But they never touch each other. Instead they push upon each other across empty space, by using e-fields and b-fields. If there wasn't any chain of electrons inside the conductor, then the EM fields would just fly off into space, like with a transmitting antenna. Wires can guide the EM energy because each electron can push the next one in sequence. But also, one electron doesn't just push on the next one. Instead, it pushes on a huge number of electrons far upstream and down the long chain of mobile charges going off into the distance. That's why the EM energy can "leapfrog" across the movable charges, at the speed of light. If each electron could only push upon its nearest neighbor, then electrical energy would travel at about the speed of sound.
- crador 10y agoLet's start with a familiar example. The speed of sound is basically fixed, and signals caused by perturbing air molecules will propagate with this speed. This is true regardless of the gross wind conditions at play -- the speed of sound is much greater than the propagation speed of any single air molecule. Similarly the speed of light is fixed, and is really the speed of propagation of electomagnetic waves. When you perturb electrons, other electrons will react to that change in the fields as it arrives at them with the speed of light. So even though the flow of electrons down the wire is very slow, the flow of energy or information may be very fast. In fact, you don't need electrons in between to move at all -- you can simply have empty space in between your antenna and the electrons you are moving around ;). As it happens, these electromagnetic waves have components that stand orthogonal to eachother. If you take relativity into account, you can find a frame of reference where the magnetic field disappears -- really the magnetic field is just a relativistic correction of the electric field and explains why charged particles attract eachother differently when moving versus at rest. In any case, it is really just one field that is called electromagnetic because we used to think it was two completely separate fields!
- justifier 10y agoFrom the linked notes: I never really understood capacitors until I started trying to construct proper water-analogies for them. Then I discovered that my electronics and physics classes had sent me down a dead-end path with their garbage about "capacitors store electric charge." Since my discovery, I've gained significantly more expertise in circuit design, which leads me to a sad thought. Maybe the more skilled of electrical engineers and scientists gain their extreme expertise not through classroom learning. Instead they gain expertise in spite of our K-12 classroom learning. Maybe the experts are experts only because they have fought free of the wrong parts of grade school science, while the rest of us are still living under the yoke of the many physics misconceptions we were carefully taught in early grades. http://amasci.com/emotor/cap1.html http://amasci.com/emotor/cap1.html
- seiferteric 10y agoNot really sure I like that link. He seems to suggest that capacitors store "energy" instead of charge, which is just as ambiguous really. It's not like there is some sort of energy particle either. Of course what's really happening is that you are creating an electric potential between two plates. It's true that the net charge is the same, but you are moving electrons from one plate and forcing them (doing work) into the other. Then when you remove the battery and have an open circuit, the potential remains because they have no way to move back to the other plate until you close the circuit again. Also, I don't think the water analogies work very well because water does not attract other water in any way, whereas in a capacitor, the electrons attraction to the electron holes in the opposing plate is an essential part of how a capacitor works and explains why the distance between the plates and the surface area are important.
- robbrown451 10y agoI think you are missing the point of the water analogies. It is what made electricity make sense to me as well. But don't take it too literally, it's an analogy, not an identity. If you start with things like "a motor is like a turbine, a generator is like a pump, a battery is like an elevated tank", a lot of things can fall into place. The point is you can visualize it.
- bandrami 10y agoIntuitive but wrong (and doggedly persistent) idea #1: "electric current is moving electrons". It is moving photons, exciting (largely) stationary electrons. I can't stress how crucial overcoming that misconception was when I was doing EE.
- palunon 10y agoHoly crap. It all make sense now. Thank you !
- pitaj 10y agoEhhhhh. Not really. It is the rate of charge passing through a cross-section. That's how it's defined, and as an EE student, what you're saying made little-to-no sense to me.
- bandrami 10y agoAnd the boson that mediates "charge" is....?
- wbeaty 10y agoNote that photons only travel along FO cable because of the charge polarization of the silica. This is a direct analog to 60Hz "electric power" traveling along a column of mobile charges in a long conductor. In both cases, the electrons wiggle back and forth, while the photons couple to them, and are guided along. But charge is not energy, in exactly the same way that amperes are not watts, and current is not EM energy-flow. Coulombs wiggle within the waveguide, while the Joules proceed continuously forward as propagating waves. The EM energy is in the form of propagating waves, while electric charge provides the medium: the waveguide.
- pitaj 10y agoPhotons don't mediate charge. The mediate the electric and magnetic fields.
- 10y ago
- Spooky23 10y agoGreat point that's really deep. One of the devilish things about science is that the mental abstraction model that works for a layperson doesn't really scratch the surface.
- ihaveahadron 10y agoI had to unlearn a shitload of made up crap that I was told. I also had to invent a lot of shit. Then I was able to get a glimpse into reality.
- dom0 10y ago+1 It took me a huge amount of time to get rid of all the BS learned in school. In some area I'm even still working on it (eg. analysis).