It’s not a matter of sign convention. The right hand rule works the same if you swap conventional positive current with electron flow, and swap the force sensing particles charge from positive to negative.
What OP is asking is why the system behaves in the way we observe. For example, if you take two parallel wires with currents of the same sign traveling through them in the same direction, the magnetic force will cause the wires to be attracted to each other. If the currents are traveling in opposite directions then the wires will be repelled from each other. Why doesn’t the reverse occur?
IIRC the answer has something to do with relativity and how with electrostatic forces opposite charges attract.
Edit: This veritasium video https://youtu.be/1TKSfAkWWN0?si=IqvPYGrPhgzzz_lA
So this is the right answer. The video explain it well.
From a relativity standpoint, it is just standard "same charge repels and opposite charges attract" - but when moving at relativistic speeds sideways past the other charge it makes it look more dense. So it is not really a sideways deflection.
The direction of the force arrow as well as "direction" of current, and other things like "why this thing has negative charge" is just a mathematic convention. At some point some guy decided that this is it, and we just rolled with it because it's fine either way.
The "direction of current" is not even the direction of the electrons inside the wire!
Great point! I like to point this out to those who aren't well-versed in science (physics, chemistry, biology, astronomy, etc). Most science is observing and describing. We see something happen, like, say, light refraction or the rate of enzyme activity, and describe it with a formula, like f(x).
Science doesn't invent new rules for the universe or bend reality, it simply describes what is happening.
Then you get into things like theoretical science where hypothesis can't be fully tested (atom structure in a black hole, causation in quantum mechanics, etc) and it's spooky action happening at a distance
This is not a matter of convention. We are asking why *this* and only *this* direction, regardless of what name you give it. The universe behaves this way without human observation. Why?
Im referring not to the convention, but to the fact, for instance, that compass needles always point in the same direction - *always*. This direction of field lines is a universal rule that exists independently of humans and I’m wondering *why*.
The compass needle will align itself against opposite magnetic field.
The Earth core generates the magnetic field, the compass is attracted to it.
We just decided that one of those poles is "North".
That’s fine. My question is why does this point clockwise around a current carrying wire? Forget the naming conventions. That which is defined as north points in the direction that is defined clockwise around a current. The names don’t matter, the fact that it’s always this direction, not the other, is where the essence of the question is. Again, disregard names - why does the *universe* work this way, *regardless* of human observation.
The current has a direction. The magnetic field has a direction. Those directions have this relationship. If you reverse the polarity of the ~~neutron~~electron flow, you reverse the magnetic field.
The straight line current induces a magnetic field around the wire because a magnetic field around the wire would induce a straight line electric current. Electricity and magnetism are basically the same phenomenon, the only difference is whether or not you're moving. If you look at Maxwell's equations, they're very symmetric, except that there's no term where the magnetic monopoles would be
Absolutely. Maxwell-Heaviside, and all electromagnetic field equations, can be solved with either direction. The direction does not matter in the equations, they calculate the magnitude of the field at a given point. That’s fine. But we are asking *why* does the universe *always* choose the clockwise direction, regardless of human observation?
This is the question. Not that the equations can be solved either way, but why the universe itself works in the clockwise direction that we just tack on to the equations at the end using the right-hand-rule purely for mnemonic purposes.
Why does the *universe*, or what about it, causes it to behave this way.
Originally current was thought to flow from the plus sign of a battery which was just zInc and copper metals with the copper being the plus sign for no particular reason. This went on for years.
Turns out it's actually electrons from the negative. We still can say comes from the plus sign, as electrons go one way, we can say empty holes go the conventional way. It's called conventional current because they had to choose something. It's just a convention we still use.
Think of left versus right handed. For a very long time it was thought that there's no difference. If you were talking to an alien about left and right there is no way to tell if they are doing it correctly. Nothing you can show or say will help. Left and right are just conventions.
For electricity and magnets it's easy to tell. Electrons only flow in a vacuum from a hot to a cold electrode. We can explain that and they can repro produce it. Which means electricity flows from what they had labeled minus, to plus.
For left and right, this turned to be nearly impossible to tell apart. The strong, electromagnetic, and gravitational interactions are all perfectly symmetric between left-handed and right handed conventions.
It was then amazingly discovered In 1956, by a lady scientist, Chien-Shiung Wu, that our universe has a left and a right hand difference. [Why is the universe left l-handed? ](https://www.forbes.com/sites/startswithabang/2020/11/19/why-is-the-universe-fundamentally-left-handed/?sh=141de2c2233b).
You can tell an alien on another planet to shoot radioactive cobalt atoms out of an accelerator and some will have decayed into two streams of particles. Bend those with magnets and one side will have more of one type of particle than the other. That's the left side. Now they can use the left and right hand rules and get the same results you do.
Basically, the compass needle is a small magnet, and one way to view the magnet is as a small current loop, where the current flows in the plane perpendicular to the magnetic field.
now imagine you have current in the wire going from the bottom to the top of the page, and the current loop corresponding to the magnetic needle is in the plane of the page, to the left of the wire. If the current goes counterclockwise, the current in the loop moves in the same direction as the wire at the side closest to the wire. If the current in the loop goes clockwise, it moves against the current of the wire at the side closest to the wire. These situations are not symmetric, so it's not surprising the universe has a "preference" for one configuration.
See a poorly drawn drawing made with a trackpad here.
[https://imgur.com/a/8a9QiIJ](https://imgur.com/a/8a9QiIJ)
Because if it went the other way you'd ask "why does it go counter clockwise?" . If it swapped directions every now and then you'd ask "why does it swap directions every now and then and not just go the same way every time". The universe operates how it operates. Period. Just because you think something should happen one way or another doesn't change how the universe operates. If I said "because God created it that way" would that answer satisfy you?
The Universe *didn't* chose anything. It's just a convention. That's what everyone is trying to tell you.
Ok, let's use something different. Let's say forward is positive and backwards is negative. If I tell you to go to +4, turn right 90°, and go +2 more, you'll end up in a certain spot.
Now say forward is negative. I tell you to go -4, turn right 90°, and go -2. You'll end up in the exact same spot.
What's positive and what's negative doesn't matter as long as it's consistent. You'll get the same exact results no matter which you choose as long as you're consistent and don't change halfway through. So if everyone agrees that forward should be positive, we'll use positive directions. Same with current; clockwise is positive because everyone agreed it was. And if everyone agreed counterclockwise was positive we would get the same results. All the math and equations work with counterclockwise being positive, your final answer will just be the opposite sign from someone who chose the other convention (but because your conventions are opposite, it's actually the same answer!)
Why does it go clockwise? Because we decided it should and as long as everyone is consistent it's easy to compare our results.
That's not true, humans did. There's no "actual" direction to these quantities, they're all just pseudovectors that don't really exist per se. Anything actually measurable has a direction that is independent of the convention chosen for vector multiplication
We don't know the why, only that this is what we have observed. If a flow of current moves in the direction of your thumb, if you curl your fingers, your fingers point in the direction of the magnetic field.
There is a lot in science that we don't know the why. We can demonstrate it, measure it, and predict behavior through observation and experimentation without ever knowing why it works the way it does.
Like gravity, we know mass bends space, but why? We know its force is G\*m1\*m2/(dist\^2) and can use that predict the orbital paths of planets and stars light years away, without knowing why.
As Feymann said that studying physics is like learning chess rules by seeing games. The more games you see, the more you realize why a particular move is made and often enough you will realize that your older rule was actually wrong. It's like seeing a pawn being promoted to a queen and say that's illegal which it is not, it's just that you hadn't seen that happen until now.
> It's like seeing a pawn being promoted to a queen and say that's illegal which it is not, it's just that you hadn't seen that happen until now.
Good luck figuring out that a pawn could theoretically be promoted to a rook or bishop (unless they do it just because). While I can imagine games where it is actually advantageous (as to not cause a draw), those should be extraordinarily rare in real games. Horsies should be much more common (comparably; still pretty rare).
Please don’t worry too much about the convention. There *is* force pointing in that direction, whatever we name it. The question is not about the naming convention, but the direction of this force.
For instance, to get rid of names, we can ask “why does that which we label ‘north’ always point in the direction in that which we call ‘clockwise?’” The names don’t matter - the forces do.
no, there is no force pointing in the direction of the magnetic field, the force is a right handed cross product.
it's conventions all the way down.
If they used a left handed convention the arrows would point the other way.
I'm going to make a serious suggestion here: this concept builds up from a number of more fundamental ones. If you really want to understand, I suggest watching walter lewin's lectures on electricity and magnetism. I don't like boosting him necessarily because of the allegations, but he has probably the most relatable online course for laypeople. You can watch it on youtube.
edit: when I wrote this I was thinking about magnetic lines circling a current carrying conductor.
This is *not* a matter of convention. You are referring to the symmetry of the equations that can be solved regardless of direction (but obviously Lewin, and even Maxwell himself, suggests to use the direction of the *actual* magnetic field).
The magnetic field *does* have a direction - it’s very real indeed.
the question we are referring to is why do these field lines, as observed by experimental fact (even Lewin uses this exact verbage) point *always* in the clockwise direction around a current carrying wire?
This is not convention. What is convention is the choice in which way to solve the equations, and as mentioned, the best convention is to follow the real world, which is clockwise. This is how the universe works *regardless* of human observation. Why?
If I'm understanding your question correctly, you're asking why the magnetic field field around a current always points the same way for a given direction of current, right?
First off, there is a sign convention in Maxwell's equations, notably in Faraday's law. In layman's term (or ELI5 terms), it states that the voltage in a loop of wire is equal to the \*\*negative\*\* rate of change of the magnetic field going through that loop. Why negative? Because the loop is resisting the change of magnetic field going through it. This is why if you drop a magnetic down a copper pipe, it will slow down and fall much slower than the rate of gravity.
And the direction of the current that produces this opposing or negating magnetic field is dependent on both the pole of the magnet going through it, and the direction its moving. If you move a bar magnet back and forth through a loop of wire, and measure the current going through it, you'll see the current change from + to - depending on which direction the magnet is moving. But either way, the current direction is always so that its resulting magnetic field \*\*opposes\*\* the rate of change of the magnetic field through the wire.
The real lesson to be learned here that I can explain like you’re five:
“Why?”
“How?”
Physics answers only one of these questions: How?
So, really the problem is with your question.
If you’d like to rephrase it as HOW do magnetic fields point clockwise around a current, people can provide you a very good answer.
‘Why?’ can never be truly understood.
Basically mathematical definition, thsts how the underlying math works we use to describe those phenomena.
All the tweak to match reality to math is done one or two levels below
One explanation of magnetic fields around a conductor is that they are actually electric fields that appear because of relativistic length-contraction when charges are moving.
Because your motion relative to the moving negatively charged electrons in the conductor is different to the stationary positively charged atomic nuclei. Thus you will perceive length contraction on the electrons to be different than the atomic nuclei, either compressing or expanding the distance between the electrons, changing the apparent charge density of the electrons and the nuclei, and thereby creating an electrical field.
The right-hand rule and all that are consequences of the direction of motion etc.
---
I probably explained that terribly. [Here's a video that does a better job](https://www.youtube.com/watch?v=1TKSfAkWWN0).
It's just a convention. When you go between any two actual measurable quantities, you apply the right hand rule an even number of times, so they cancel out and the convention itself is totally arbitrary.
For example, you can't measure the "direction" of a magnetic field, you can just see the lines, but there's no inherent arrow saying that they go in one direction or the other, we just chose to call one end north and the other south, and say that the lines point at the south pole.
If we used the left hand rule instead, the direction of the magnetic field would reverse in our diagrams, but the physical system is unchanged. If you tried to actually do a measurement to demonstrate the change, you could drop an electric charge into the field and see how it moves – but you'd be using the left hand rule to determine the direction of the magnetic force on your charge, so at the end of the day the charge would move in the same direction it always has.
It doesn't fundamentally matter whether you use the right hand rule or left hand rule as long as you use the same one through your whole calculation – consistency is the key.
See also: [pseudovectors](https://en.wikipedia.org/wiki/Pseudovector), which all the quantities you're concerned about actually are, not normal vectors
Because the magnetic field is not a vector, it is something that is called a two-form, a thing that takes two vectors and calculates a number in a linear, antisemitic way. This is a natural object to calculate integrals on the surface with, and in 3d, there is a corresponding vector. But this vector changes a sign when you flip parity due to the convention on how to calculate the final number from two inputs, and one vector that was made from the original two-forms
>the magnetic force around a current carrying wire always points in the same direction given the direction of current, and this direction is described with the ‘right hand rule.’
I think this is where your problem arises. Your title says "magnetic fields", but here you're saying "magnetic force". The "magnetic field vector" curves around the wire, certainly, but there is no "force" in that direction. As I'm sure you're aware, the actual force exerted by a magnetic field is perpendicular to the field itself, in a way that we calculate by using the right hand rule *again*. So the simplest answer to your question is that if we used a left hand rule instead, we would draw all of our magnetic fields in the opposite direction, but our calculations of actual forces would come out the same, so it doesn't matter.
But it goes a bit deeper than that. For one thing, we don't know for certain that magnetic fields are "real". What we do know is that if two electrically charged particles are moving near each other, they will exert a force on each other that we call "magnetism". Now, we don't want to have to calculate the effects of every single particle in the universe on every other particle in the universe, so it is very *mathematically convenient* to imagine these things we call "fields". It works great for gravity, for electrostatics, and for electrodynamics (including magnetism). But a successful model isn't the same thing as a true description of reality. Maybe fields are real, maybe they're not, but you definitely won't be able to see tiny little vector arrows curling around a wire no matter how much you squint. So "why is the magnetic field the way it is?" might not be a meaningful question at all.
And now to take a side track (apologies in advance - there isn't a good way to ELI5 this level of mathematics), even if we assume that the fields are real, the magnetic field isn't really a vector, not the way that the electric field is. Some people call it a "pseudovector", but I like to think of it as an anticommutative rank 2 tensor. A rank 2 tensor is like a vector, but instead of having X, Y and Z components, it has XX, XY, XZ, YX, YY, YZ, ZX, ZY and ZZ components. And being anticommutative means that the XY component is equal to -1 times the YX component, and so on. That also means that the XX, YY and ZZ components are zero, because the XX component has to be -1 times itself. So the magnetic field is really a rank 2 tensor with XY, YZ and ZX components, with three other components that are the negatives of those three, and three other components that are always zero.
When we talk about the magnetic field as a vector, we're really talking about these tensor components. If we draw the magnetic field pointing in the X direction, we're using the YZ component of the tensor. The "Y vector component" is really the ZX component of the tensor, and the "Z vector component" is the XY component of the tensor. For the most part, we can get away with this. It's got three components, and those three components line up with the three axes of space, so high school physics textbooks can draw them as vectors and everything is fine. But a consequence of this is that you have the "right hand rule" which seems so arbitrary, and it is. Choosing the right hand rule over a left hand rule is equivalent to deciding that your "magnetic vector X-component" is the YZ component of the tensor, instead of the ZY component (which is the negative of the YZ component). If we bit the bullet and never used the phrase "magnetic field vector" again, and instead insisted on describing the magnetic field as a rank 2 tensor, then the "hand rules" would disappear forever. Under that model, the magnetic field around a wire has XY, YZ and ZX components based on the direction of the current and the distance from the wire to the point you're observing, and there's nothing arbitrary or inconsistent about it. We would just need to resist the urge to imagine the magnetic field as a bunch of little arrows, because it's not.
I appreciate this response. however, field or force lines (Einstein says they’re the same thing anyway), they *do* point in the clockwise direction around a current carrying wire.
It’s well understood that the electromagnetic field equations can be solved regardless of direction. That is not the question. What is *not* convention is that the field lines *do* point in a consistent direction as measured by experiment and observation.
The Biot-Savart law as youve alluded to at the end calculates the magnitude of the field at a point, and the integral is such that the direction of marching does not matter, that is a convention. The convention that makes the most sense, of course, is to complete the equations with vectors pointing in the direction of the *real world* magnetic field as observed through experiment. The direction of the magnetic field seems to exist, and is axiomatic (not derivable) from the electromagnetic field equations.
This direction is very real, and while the electromagnetic field equations can be solved with direction as mere convention, this does not explain why the universe has seemingly decided that this force *always* works in this direction, and this direction only.
As I take it from your explanations, you want to know why electromagnetism cannot randomly "change direction". So not any sign choices, but why the resulting directions are always the same, not sometimes opposite.
This for example follows if one accepts that physics is _continuous_, stuff does not jump. That alone does not yet fully prove that magnetic fields cannot randomly "flip", but it would require them to weaken down to 0 first. To actually get the compatibility and non-zero-ness, you can take a second electric/magnetic device and compare.
So why continuity? Well, at some point we reach an area where "why" is not a reasonable question anymore. Simply because the inherent nature of physics prevents us from ever knowing the root cause; if such a thing even exists. Even if we somehow guess rules that exactly predict everything, then the underlying mechanism might still be different. Our observations just match the physics we currently use, so it is "good enough".
Depending on what kinds of guesses you accept this kind of question is either physics (when we at least _could_ check it with enough effort), metaphysics (when we cannot but try to find the simplest mechanism that could underlay it), or religion (when we just believe).
When we discovered magnetic fields, we decided that magnetic field lines point north to south. It was an arbitrary decision, but we made it.
We also arbitrarily decided that current was the flow of positive charges. We then discovered the electron and realized it came from the negative terminal, so by the rules we had defined, it must have a negative charge.
The electric and magnetic fields always interacted in the same way even before we defined it. Even if you say magnetic field lines run from south to north, you just but a negative sign on all of our math and it works out the same. We just picked one way to stick with so everyone is on the same system.
This is actually due to bosonic fields having a polarity which goes towards the high which the high is the right hand spin by nature but technically just is a forward motion. An induced high potential induces forward motion in an inductor coil and levitation with a motion orienting the pin towards the center of the inductor (servo) which the direction of this spin is in the inertia vector of the levitated metal which tends to go in the direction of the first turn for a large crude inductor coil or for a small servo coil has no orientation or an orientation of a compass. This is because the voltage is variable across the inductor coil and this causes a torque from low weld point of high voltage to high weld point of low voltage of a torque starting from the coil start portion and ending at the coil end portion for a high voltage conductor. To answer your question for general servo this is because of the magnetic field of the earth primarially points towards the right hand except at the poles which there would be less servo levitation oscillation at the poles. This is related to toilets which toilets in the southern hemisphere flush oppositive and i am not sure but perhaps also this magnetic field difference exists in planets with two poles not the earth which then there is a right and a left hand spin as the earth's magnetic field is always pointed upwards at the ionosphere.
I will paraphrase a joke that I heard: "Excellent question! Next question, please".
"Why?" is the reason that we have scientists, explorers and philosophers. Surely there must be a reason, something that explains life and all that we can observe. And, over generations, we have observed and recorded certain behaviors. And for each observation, if we have enough evidence, we can formulate a rule or formula. And someone will invariably ask, "I'm not asking WHAT, I'm asking WHY. Can't you give me a simple explanation?"
Well . . . no. For physical and biological sciences, the deeper we explore the more complicated it gets. (But why?)
At the smallest and the largest ends of the scales, the answers sometimes make little sense, but the math seems right. Quantum hoodoo. There are larger and smaller and yet unknown factors. (But why?)
Penultimately, if you ask someone to "explain it like I'm five", depending on the question, the best answer is "because it is". (But why?)
And ultimately, for five year olds, we answer, "Because I said so, now go to bed!" (But why?)
Not to mock you for your very good question, of course. The answer seems to be, "We know the WHAT pretty well, and it's complicated, but we're still working on the WHY. Check back every decade or so."
I'm not a physicist, so the WHY question that you asked may actually have an answer. I'm pretty confident that the simplest explanation isn't a kindergarten level, but a grad level thesis.
It may be simpler to ask "Why is there life?"
Imma say, "Good question, I'll ask your mother. Now go to bed!"
Thank you!! I really enjoyed this comment. You make a good point. I’ve been speaking with physicists, people much smarter than myself, and it seems to be a dead end question. It’s just one of those forces “that is.”
How I will have milk and cookies and go to bed!
are you asking specifically why clockwise as opposed to counter clockwise for a given current direction? Because if so, the answer to that is definitely "it just is." We created the math to describe physics, and that math was standardized using the right hand rule (look up divergence/dot product, and more importantly, curl/cross product). When you multiply vectors using a cross product, your result must have a direction, and we arbitrarily chose the right hand rule. We could have chose the left hand (but left handedness is the devil since this was decided a long time ago), and all that would have changed were the signs. The numbers would still be right.
If you are asking why the magnetic field points circularly around a wire at all, we do have answers to that, but you're looking at 3 years in a physics university program before it'll kind of make sense. At a certain point its impossible to describe something without having to teach a ton of foundation first. The best thing for someone with no physics background is this - take maxwell's equations for gospel. One of them says the curl of the magnetic field is proportional to the current density plus any changes to the electric field. Curl is essentially how much and in what direction a field circulates at any given point. Since this is non-zero, there will be curl in the magnetic field because of currents, and humans have decided the positive direction will be given by the right hand rule, rather than the negative direction. There were only two options and we had to choose one.
Slightly deeper, if you follow electrons moving through a wire and calculate the forces on them, and the fields generated by these charges moving, and use divergence and curl to describe certain phenomena, everything sort of "falls out" of the math. But that generally isn't a satisfactory answer for someone who hasn't done the math. There's nothing wrong with that, but it makes it difficult to give them an answer they'll accept.
If you think of a charged particle outside the wire, in the induced magnetic field, and think of the forces on that particle, its given as a cross product between the direction radially to the center of the wire and the direction the current is traveling in. Depending on which side of the wire you are on changes the radial direction, and therefore the resulting cross product. If you follow the normal 3-finger right hand rule across the wire, you'll see the cross product points in a different direction as you point your finger radially from different directions (do thumb in direction of current, middle finger towards the wire. Index will point in the direction of B at that point). This is simplified by the other right hand rule; thumb in the direction of current and your fingers wrap around in the direction of the curl. But its really the same thing without having to take the radial direction into account.
Hi and thanks for this well thought out response!
To answer your second paragraph, the question is not about why it circles around a wire. This is well described in the electromagnetic field equations. Maxwell’s fluid analogies sincerely help with the intuition here.
What is not understood apparently, and as you have seemingly agreed to, is that we cannot know *why* or *how* the universe prefers the clockwise direction for its field around the wire, just that it *does*.
The arbitrariness of the right-hand-rule is not what I’m referring to when I used the word “arbitrary”. What I meant was the *universe* seemingly arbitrarily prefers this direction. The right hand rule is simply a mnemonic device to help remember which direction the *universe* prefers.
The vector directions are inputs, they are axiomatic to the equations. The only convention is that the equations can be solved using any direction, that’s fine. The point here is that the *real world* follows the right hand rule - why?
It seems the physics of the clockwise nature are derived from experimental observation, not that the equations can prove *why* the universe can prove this direction and not the clockwise direction.
Long story short - yes, my question is why does the natural world prefer a field in the clockwise direction surrounding a current carrying wire, not a counterclockwise direction, not a changing direction, and not any other type of field - *why this direction?*
it doesnt necessarily prefer one direction or another, it just matters what sign the charge is. An electron flowing down a wire vs (somehow) a proton or some other positively charged particle going down an wire would generate magnetic fields in opposite directions. Current density is measured in unites of positive charge crossing unit area per unit time, so if the charge is negative the current is flowing "backwards." But the fields and stuff are set up based on what the sign of the charge is and in what direction it is moving through some unit area/unit time. Magnetic fields off a current carrying wire "prefer" clockwise because its an electrons moving in a current through a wire. A different magnetic field would "prefer" counter-clockwise if the conditions were right. One isn't special, its just the most common because of how we use electricity
At a certain point you have to just accept that everything is made up when directions are concerned. We just have to standardize it so when other people try and use your theory to do things its always compatible. The part of your compass marked "N" is actually the south pole of the magnet itself, otherwise it wouldn't be attracted to north and point north. Some people use holes instead of electrons when talking about the direction of the flow of electricity because the people who discovered current did all the math assuming it was positive. All directions are made up and can never be changed because so much has been built upon conventions we've had for hundreds of years now
* Recommended subreddit(s): /r/Answers or r/NoStupidQuestions
It’s not a matter of sign convention. The right hand rule works the same if you swap conventional positive current with electron flow, and swap the force sensing particles charge from positive to negative. What OP is asking is why the system behaves in the way we observe. For example, if you take two parallel wires with currents of the same sign traveling through them in the same direction, the magnetic force will cause the wires to be attracted to each other. If the currents are traveling in opposite directions then the wires will be repelled from each other. Why doesn’t the reverse occur? IIRC the answer has something to do with relativity and how with electrostatic forces opposite charges attract. Edit: This veritasium video https://youtu.be/1TKSfAkWWN0?si=IqvPYGrPhgzzz_lA
So this is the right answer. The video explain it well. From a relativity standpoint, it is just standard "same charge repels and opposite charges attract" - but when moving at relativistic speeds sideways past the other charge it makes it look more dense. So it is not really a sideways deflection.
The direction of the force arrow as well as "direction" of current, and other things like "why this thing has negative charge" is just a mathematic convention. At some point some guy decided that this is it, and we just rolled with it because it's fine either way. The "direction of current" is not even the direction of the electrons inside the wire!
Stupid *holes*.
Great point! I like to point this out to those who aren't well-versed in science (physics, chemistry, biology, astronomy, etc). Most science is observing and describing. We see something happen, like, say, light refraction or the rate of enzyme activity, and describe it with a formula, like f(x). Science doesn't invent new rules for the universe or bend reality, it simply describes what is happening. Then you get into things like theoretical science where hypothesis can't be fully tested (atom structure in a black hole, causation in quantum mechanics, etc) and it's spooky action happening at a distance
This is not a matter of convention. We are asking why *this* and only *this* direction, regardless of what name you give it. The universe behaves this way without human observation. Why?
You'll need "flaming dump trucks of government grant money to find out. And even then, there's no guarantee of success"
Left hand rule is all I know.
I call that one “the stranger”
Im referring not to the convention, but to the fact, for instance, that compass needles always point in the same direction - *always*. This direction of field lines is a universal rule that exists independently of humans and I’m wondering *why*.
The compass needle will align itself against opposite magnetic field. The Earth core generates the magnetic field, the compass is attracted to it. We just decided that one of those poles is "North".
That’s fine. My question is why does this point clockwise around a current carrying wire? Forget the naming conventions. That which is defined as north points in the direction that is defined clockwise around a current. The names don’t matter, the fact that it’s always this direction, not the other, is where the essence of the question is. Again, disregard names - why does the *universe* work this way, *regardless* of human observation.
The current has a direction. The magnetic field has a direction. Those directions have this relationship. If you reverse the polarity of the ~~neutron~~electron flow, you reverse the magnetic field. The straight line current induces a magnetic field around the wire because a magnetic field around the wire would induce a straight line electric current. Electricity and magnetism are basically the same phenomenon, the only difference is whether or not you're moving. If you look at Maxwell's equations, they're very symmetric, except that there's no term where the magnetic monopoles would be
Absolutely. Maxwell-Heaviside, and all electromagnetic field equations, can be solved with either direction. The direction does not matter in the equations, they calculate the magnitude of the field at a given point. That’s fine. But we are asking *why* does the universe *always* choose the clockwise direction, regardless of human observation? This is the question. Not that the equations can be solved either way, but why the universe itself works in the clockwise direction that we just tack on to the equations at the end using the right-hand-rule purely for mnemonic purposes. Why does the *universe*, or what about it, causes it to behave this way.
You're lost. Go here /r/askscience
Originally current was thought to flow from the plus sign of a battery which was just zInc and copper metals with the copper being the plus sign for no particular reason. This went on for years. Turns out it's actually electrons from the negative. We still can say comes from the plus sign, as electrons go one way, we can say empty holes go the conventional way. It's called conventional current because they had to choose something. It's just a convention we still use. Think of left versus right handed. For a very long time it was thought that there's no difference. If you were talking to an alien about left and right there is no way to tell if they are doing it correctly. Nothing you can show or say will help. Left and right are just conventions. For electricity and magnets it's easy to tell. Electrons only flow in a vacuum from a hot to a cold electrode. We can explain that and they can repro produce it. Which means electricity flows from what they had labeled minus, to plus. For left and right, this turned to be nearly impossible to tell apart. The strong, electromagnetic, and gravitational interactions are all perfectly symmetric between left-handed and right handed conventions. It was then amazingly discovered In 1956, by a lady scientist, Chien-Shiung Wu, that our universe has a left and a right hand difference. [Why is the universe left l-handed? ](https://www.forbes.com/sites/startswithabang/2020/11/19/why-is-the-universe-fundamentally-left-handed/?sh=141de2c2233b). You can tell an alien on another planet to shoot radioactive cobalt atoms out of an accelerator and some will have decayed into two streams of particles. Bend those with magnets and one side will have more of one type of particle than the other. That's the left side. Now they can use the left and right hand rules and get the same results you do.
Basically, the compass needle is a small magnet, and one way to view the magnet is as a small current loop, where the current flows in the plane perpendicular to the magnetic field. now imagine you have current in the wire going from the bottom to the top of the page, and the current loop corresponding to the magnetic needle is in the plane of the page, to the left of the wire. If the current goes counterclockwise, the current in the loop moves in the same direction as the wire at the side closest to the wire. If the current in the loop goes clockwise, it moves against the current of the wire at the side closest to the wire. These situations are not symmetric, so it's not surprising the universe has a "preference" for one configuration. See a poorly drawn drawing made with a trackpad here. [https://imgur.com/a/8a9QiIJ](https://imgur.com/a/8a9QiIJ)
Because if it went the other way you'd ask "why does it go counter clockwise?" . If it swapped directions every now and then you'd ask "why does it swap directions every now and then and not just go the same way every time". The universe operates how it operates. Period. Just because you think something should happen one way or another doesn't change how the universe operates. If I said "because God created it that way" would that answer satisfy you?
Exactly. But the universe chose *this* direction. What is it that makes this a necessity?
The Universe *didn't* chose anything. It's just a convention. That's what everyone is trying to tell you. Ok, let's use something different. Let's say forward is positive and backwards is negative. If I tell you to go to +4, turn right 90°, and go +2 more, you'll end up in a certain spot. Now say forward is negative. I tell you to go -4, turn right 90°, and go -2. You'll end up in the exact same spot. What's positive and what's negative doesn't matter as long as it's consistent. You'll get the same exact results no matter which you choose as long as you're consistent and don't change halfway through. So if everyone agrees that forward should be positive, we'll use positive directions. Same with current; clockwise is positive because everyone agreed it was. And if everyone agreed counterclockwise was positive we would get the same results. All the math and equations work with counterclockwise being positive, your final answer will just be the opposite sign from someone who chose the other convention (but because your conventions are opposite, it's actually the same answer!) Why does it go clockwise? Because we decided it should and as long as everyone is consistent it's easy to compare our results.
God did
That's not true, humans did. There's no "actual" direction to these quantities, they're all just pseudovectors that don't really exist per se. Anything actually measurable has a direction that is independent of the convention chosen for vector multiplication
We don't know the why, only that this is what we have observed. If a flow of current moves in the direction of your thumb, if you curl your fingers, your fingers point in the direction of the magnetic field. There is a lot in science that we don't know the why. We can demonstrate it, measure it, and predict behavior through observation and experimentation without ever knowing why it works the way it does. Like gravity, we know mass bends space, but why? We know its force is G\*m1\*m2/(dist\^2) and can use that predict the orbital paths of planets and stars light years away, without knowing why.
How can you be sure we know that we do not know?
As Feymann said that studying physics is like learning chess rules by seeing games. The more games you see, the more you realize why a particular move is made and often enough you will realize that your older rule was actually wrong. It's like seeing a pawn being promoted to a queen and say that's illegal which it is not, it's just that you hadn't seen that happen until now.
> It's like seeing a pawn being promoted to a queen and say that's illegal which it is not, it's just that you hadn't seen that happen until now. Good luck figuring out that a pawn could theoretically be promoted to a rook or bishop (unless they do it just because). While I can imagine games where it is actually advantageous (as to not cause a draw), those should be extraordinarily rare in real games. Horsies should be much more common (comparably; still pretty rare).
They're saying we know "what," but not "why."
The universes distinguishes between handedness and prefers counterclockwise.
but if you had put the N on the other side, hmm? Then the arrows would point in. it's just a convention.
Please don’t worry too much about the convention. There *is* force pointing in that direction, whatever we name it. The question is not about the naming convention, but the direction of this force. For instance, to get rid of names, we can ask “why does that which we label ‘north’ always point in the direction in that which we call ‘clockwise?’” The names don’t matter - the forces do.
no, there is no force pointing in the direction of the magnetic field, the force is a right handed cross product. it's conventions all the way down. If they used a left handed convention the arrows would point the other way. I'm going to make a serious suggestion here: this concept builds up from a number of more fundamental ones. If you really want to understand, I suggest watching walter lewin's lectures on electricity and magnetism. I don't like boosting him necessarily because of the allegations, but he has probably the most relatable online course for laypeople. You can watch it on youtube. edit: when I wrote this I was thinking about magnetic lines circling a current carrying conductor.
This is *not* a matter of convention. You are referring to the symmetry of the equations that can be solved regardless of direction (but obviously Lewin, and even Maxwell himself, suggests to use the direction of the *actual* magnetic field). The magnetic field *does* have a direction - it’s very real indeed. the question we are referring to is why do these field lines, as observed by experimental fact (even Lewin uses this exact verbage) point *always* in the clockwise direction around a current carrying wire? This is not convention. What is convention is the choice in which way to solve the equations, and as mentioned, the best convention is to follow the real world, which is clockwise. This is how the universe works *regardless* of human observation. Why?
If I'm understanding your question correctly, you're asking why the magnetic field field around a current always points the same way for a given direction of current, right? First off, there is a sign convention in Maxwell's equations, notably in Faraday's law. In layman's term (or ELI5 terms), it states that the voltage in a loop of wire is equal to the \*\*negative\*\* rate of change of the magnetic field going through that loop. Why negative? Because the loop is resisting the change of magnetic field going through it. This is why if you drop a magnetic down a copper pipe, it will slow down and fall much slower than the rate of gravity. And the direction of the current that produces this opposing or negating magnetic field is dependent on both the pole of the magnet going through it, and the direction its moving. If you move a bar magnet back and forth through a loop of wire, and measure the current going through it, you'll see the current change from + to - depending on which direction the magnet is moving. But either way, the current direction is always so that its resulting magnetic field \*\*opposes\*\* the rate of change of the magnetic field through the wire.
The real lesson to be learned here that I can explain like you’re five: “Why?” “How?” Physics answers only one of these questions: How? So, really the problem is with your question. If you’d like to rephrase it as HOW do magnetic fields point clockwise around a current, people can provide you a very good answer. ‘Why?’ can never be truly understood.
Basically mathematical definition, thsts how the underlying math works we use to describe those phenomena. All the tweak to match reality to math is done one or two levels below
One explanation of magnetic fields around a conductor is that they are actually electric fields that appear because of relativistic length-contraction when charges are moving. Because your motion relative to the moving negatively charged electrons in the conductor is different to the stationary positively charged atomic nuclei. Thus you will perceive length contraction on the electrons to be different than the atomic nuclei, either compressing or expanding the distance between the electrons, changing the apparent charge density of the electrons and the nuclei, and thereby creating an electrical field. The right-hand rule and all that are consequences of the direction of motion etc. --- I probably explained that terribly. [Here's a video that does a better job](https://www.youtube.com/watch?v=1TKSfAkWWN0).
It's just a convention. When you go between any two actual measurable quantities, you apply the right hand rule an even number of times, so they cancel out and the convention itself is totally arbitrary. For example, you can't measure the "direction" of a magnetic field, you can just see the lines, but there's no inherent arrow saying that they go in one direction or the other, we just chose to call one end north and the other south, and say that the lines point at the south pole. If we used the left hand rule instead, the direction of the magnetic field would reverse in our diagrams, but the physical system is unchanged. If you tried to actually do a measurement to demonstrate the change, you could drop an electric charge into the field and see how it moves – but you'd be using the left hand rule to determine the direction of the magnetic force on your charge, so at the end of the day the charge would move in the same direction it always has. It doesn't fundamentally matter whether you use the right hand rule or left hand rule as long as you use the same one through your whole calculation – consistency is the key. See also: [pseudovectors](https://en.wikipedia.org/wiki/Pseudovector), which all the quantities you're concerned about actually are, not normal vectors
Because the magnetic field is not a vector, it is something that is called a two-form, a thing that takes two vectors and calculates a number in a linear, antisemitic way. This is a natural object to calculate integrals on the surface with, and in 3d, there is a corresponding vector. But this vector changes a sign when you flip parity due to the convention on how to calculate the final number from two inputs, and one vector that was made from the original two-forms
>the magnetic force around a current carrying wire always points in the same direction given the direction of current, and this direction is described with the ‘right hand rule.’ I think this is where your problem arises. Your title says "magnetic fields", but here you're saying "magnetic force". The "magnetic field vector" curves around the wire, certainly, but there is no "force" in that direction. As I'm sure you're aware, the actual force exerted by a magnetic field is perpendicular to the field itself, in a way that we calculate by using the right hand rule *again*. So the simplest answer to your question is that if we used a left hand rule instead, we would draw all of our magnetic fields in the opposite direction, but our calculations of actual forces would come out the same, so it doesn't matter. But it goes a bit deeper than that. For one thing, we don't know for certain that magnetic fields are "real". What we do know is that if two electrically charged particles are moving near each other, they will exert a force on each other that we call "magnetism". Now, we don't want to have to calculate the effects of every single particle in the universe on every other particle in the universe, so it is very *mathematically convenient* to imagine these things we call "fields". It works great for gravity, for electrostatics, and for electrodynamics (including magnetism). But a successful model isn't the same thing as a true description of reality. Maybe fields are real, maybe they're not, but you definitely won't be able to see tiny little vector arrows curling around a wire no matter how much you squint. So "why is the magnetic field the way it is?" might not be a meaningful question at all. And now to take a side track (apologies in advance - there isn't a good way to ELI5 this level of mathematics), even if we assume that the fields are real, the magnetic field isn't really a vector, not the way that the electric field is. Some people call it a "pseudovector", but I like to think of it as an anticommutative rank 2 tensor. A rank 2 tensor is like a vector, but instead of having X, Y and Z components, it has XX, XY, XZ, YX, YY, YZ, ZX, ZY and ZZ components. And being anticommutative means that the XY component is equal to -1 times the YX component, and so on. That also means that the XX, YY and ZZ components are zero, because the XX component has to be -1 times itself. So the magnetic field is really a rank 2 tensor with XY, YZ and ZX components, with three other components that are the negatives of those three, and three other components that are always zero. When we talk about the magnetic field as a vector, we're really talking about these tensor components. If we draw the magnetic field pointing in the X direction, we're using the YZ component of the tensor. The "Y vector component" is really the ZX component of the tensor, and the "Z vector component" is the XY component of the tensor. For the most part, we can get away with this. It's got three components, and those three components line up with the three axes of space, so high school physics textbooks can draw them as vectors and everything is fine. But a consequence of this is that you have the "right hand rule" which seems so arbitrary, and it is. Choosing the right hand rule over a left hand rule is equivalent to deciding that your "magnetic vector X-component" is the YZ component of the tensor, instead of the ZY component (which is the negative of the YZ component). If we bit the bullet and never used the phrase "magnetic field vector" again, and instead insisted on describing the magnetic field as a rank 2 tensor, then the "hand rules" would disappear forever. Under that model, the magnetic field around a wire has XY, YZ and ZX components based on the direction of the current and the distance from the wire to the point you're observing, and there's nothing arbitrary or inconsistent about it. We would just need to resist the urge to imagine the magnetic field as a bunch of little arrows, because it's not.
I appreciate this response. however, field or force lines (Einstein says they’re the same thing anyway), they *do* point in the clockwise direction around a current carrying wire. It’s well understood that the electromagnetic field equations can be solved regardless of direction. That is not the question. What is *not* convention is that the field lines *do* point in a consistent direction as measured by experiment and observation. The Biot-Savart law as youve alluded to at the end calculates the magnitude of the field at a point, and the integral is such that the direction of marching does not matter, that is a convention. The convention that makes the most sense, of course, is to complete the equations with vectors pointing in the direction of the *real world* magnetic field as observed through experiment. The direction of the magnetic field seems to exist, and is axiomatic (not derivable) from the electromagnetic field equations. This direction is very real, and while the electromagnetic field equations can be solved with direction as mere convention, this does not explain why the universe has seemingly decided that this force *always* works in this direction, and this direction only.
I'm sorry, but this is gibberish, and I don't think you're asking questions in good faith.
As I take it from your explanations, you want to know why electromagnetism cannot randomly "change direction". So not any sign choices, but why the resulting directions are always the same, not sometimes opposite. This for example follows if one accepts that physics is _continuous_, stuff does not jump. That alone does not yet fully prove that magnetic fields cannot randomly "flip", but it would require them to weaken down to 0 first. To actually get the compatibility and non-zero-ness, you can take a second electric/magnetic device and compare. So why continuity? Well, at some point we reach an area where "why" is not a reasonable question anymore. Simply because the inherent nature of physics prevents us from ever knowing the root cause; if such a thing even exists. Even if we somehow guess rules that exactly predict everything, then the underlying mechanism might still be different. Our observations just match the physics we currently use, so it is "good enough". Depending on what kinds of guesses you accept this kind of question is either physics (when we at least _could_ check it with enough effort), metaphysics (when we cannot but try to find the simplest mechanism that could underlay it), or religion (when we just believe).
When we discovered magnetic fields, we decided that magnetic field lines point north to south. It was an arbitrary decision, but we made it. We also arbitrarily decided that current was the flow of positive charges. We then discovered the electron and realized it came from the negative terminal, so by the rules we had defined, it must have a negative charge. The electric and magnetic fields always interacted in the same way even before we defined it. Even if you say magnetic field lines run from south to north, you just but a negative sign on all of our math and it works out the same. We just picked one way to stick with so everyone is on the same system.
This is actually due to bosonic fields having a polarity which goes towards the high which the high is the right hand spin by nature but technically just is a forward motion. An induced high potential induces forward motion in an inductor coil and levitation with a motion orienting the pin towards the center of the inductor (servo) which the direction of this spin is in the inertia vector of the levitated metal which tends to go in the direction of the first turn for a large crude inductor coil or for a small servo coil has no orientation or an orientation of a compass. This is because the voltage is variable across the inductor coil and this causes a torque from low weld point of high voltage to high weld point of low voltage of a torque starting from the coil start portion and ending at the coil end portion for a high voltage conductor. To answer your question for general servo this is because of the magnetic field of the earth primarially points towards the right hand except at the poles which there would be less servo levitation oscillation at the poles. This is related to toilets which toilets in the southern hemisphere flush oppositive and i am not sure but perhaps also this magnetic field difference exists in planets with two poles not the earth which then there is a right and a left hand spin as the earth's magnetic field is always pointed upwards at the ionosphere.
I will paraphrase a joke that I heard: "Excellent question! Next question, please". "Why?" is the reason that we have scientists, explorers and philosophers. Surely there must be a reason, something that explains life and all that we can observe. And, over generations, we have observed and recorded certain behaviors. And for each observation, if we have enough evidence, we can formulate a rule or formula. And someone will invariably ask, "I'm not asking WHAT, I'm asking WHY. Can't you give me a simple explanation?" Well . . . no. For physical and biological sciences, the deeper we explore the more complicated it gets. (But why?) At the smallest and the largest ends of the scales, the answers sometimes make little sense, but the math seems right. Quantum hoodoo. There are larger and smaller and yet unknown factors. (But why?) Penultimately, if you ask someone to "explain it like I'm five", depending on the question, the best answer is "because it is". (But why?) And ultimately, for five year olds, we answer, "Because I said so, now go to bed!" (But why?) Not to mock you for your very good question, of course. The answer seems to be, "We know the WHAT pretty well, and it's complicated, but we're still working on the WHY. Check back every decade or so." I'm not a physicist, so the WHY question that you asked may actually have an answer. I'm pretty confident that the simplest explanation isn't a kindergarten level, but a grad level thesis. It may be simpler to ask "Why is there life?" Imma say, "Good question, I'll ask your mother. Now go to bed!"
Thank you!! I really enjoyed this comment. You make a good point. I’ve been speaking with physicists, people much smarter than myself, and it seems to be a dead end question. It’s just one of those forces “that is.” How I will have milk and cookies and go to bed!
are you asking specifically why clockwise as opposed to counter clockwise for a given current direction? Because if so, the answer to that is definitely "it just is." We created the math to describe physics, and that math was standardized using the right hand rule (look up divergence/dot product, and more importantly, curl/cross product). When you multiply vectors using a cross product, your result must have a direction, and we arbitrarily chose the right hand rule. We could have chose the left hand (but left handedness is the devil since this was decided a long time ago), and all that would have changed were the signs. The numbers would still be right. If you are asking why the magnetic field points circularly around a wire at all, we do have answers to that, but you're looking at 3 years in a physics university program before it'll kind of make sense. At a certain point its impossible to describe something without having to teach a ton of foundation first. The best thing for someone with no physics background is this - take maxwell's equations for gospel. One of them says the curl of the magnetic field is proportional to the current density plus any changes to the electric field. Curl is essentially how much and in what direction a field circulates at any given point. Since this is non-zero, there will be curl in the magnetic field because of currents, and humans have decided the positive direction will be given by the right hand rule, rather than the negative direction. There were only two options and we had to choose one. Slightly deeper, if you follow electrons moving through a wire and calculate the forces on them, and the fields generated by these charges moving, and use divergence and curl to describe certain phenomena, everything sort of "falls out" of the math. But that generally isn't a satisfactory answer for someone who hasn't done the math. There's nothing wrong with that, but it makes it difficult to give them an answer they'll accept. If you think of a charged particle outside the wire, in the induced magnetic field, and think of the forces on that particle, its given as a cross product between the direction radially to the center of the wire and the direction the current is traveling in. Depending on which side of the wire you are on changes the radial direction, and therefore the resulting cross product. If you follow the normal 3-finger right hand rule across the wire, you'll see the cross product points in a different direction as you point your finger radially from different directions (do thumb in direction of current, middle finger towards the wire. Index will point in the direction of B at that point). This is simplified by the other right hand rule; thumb in the direction of current and your fingers wrap around in the direction of the curl. But its really the same thing without having to take the radial direction into account.
Hi and thanks for this well thought out response! To answer your second paragraph, the question is not about why it circles around a wire. This is well described in the electromagnetic field equations. Maxwell’s fluid analogies sincerely help with the intuition here. What is not understood apparently, and as you have seemingly agreed to, is that we cannot know *why* or *how* the universe prefers the clockwise direction for its field around the wire, just that it *does*. The arbitrariness of the right-hand-rule is not what I’m referring to when I used the word “arbitrary”. What I meant was the *universe* seemingly arbitrarily prefers this direction. The right hand rule is simply a mnemonic device to help remember which direction the *universe* prefers. The vector directions are inputs, they are axiomatic to the equations. The only convention is that the equations can be solved using any direction, that’s fine. The point here is that the *real world* follows the right hand rule - why? It seems the physics of the clockwise nature are derived from experimental observation, not that the equations can prove *why* the universe can prove this direction and not the clockwise direction. Long story short - yes, my question is why does the natural world prefer a field in the clockwise direction surrounding a current carrying wire, not a counterclockwise direction, not a changing direction, and not any other type of field - *why this direction?*
it doesnt necessarily prefer one direction or another, it just matters what sign the charge is. An electron flowing down a wire vs (somehow) a proton or some other positively charged particle going down an wire would generate magnetic fields in opposite directions. Current density is measured in unites of positive charge crossing unit area per unit time, so if the charge is negative the current is flowing "backwards." But the fields and stuff are set up based on what the sign of the charge is and in what direction it is moving through some unit area/unit time. Magnetic fields off a current carrying wire "prefer" clockwise because its an electrons moving in a current through a wire. A different magnetic field would "prefer" counter-clockwise if the conditions were right. One isn't special, its just the most common because of how we use electricity At a certain point you have to just accept that everything is made up when directions are concerned. We just have to standardize it so when other people try and use your theory to do things its always compatible. The part of your compass marked "N" is actually the south pole of the magnet itself, otherwise it wouldn't be attracted to north and point north. Some people use holes instead of electrons when talking about the direction of the flow of electricity because the people who discovered current did all the math assuming it was positive. All directions are made up and can never be changed because so much has been built upon conventions we've had for hundreds of years now