# Magnetism & Matter: Q&A on Electrons & Fields

• Prannoy Mehta
In summary, a wire of current I am moving in +y axis and a electron is revolving at a distance of x m along +k direction, does it feel any magnetic force, and what if it was spinning along +y direction.thanks for clearing the doubts.
Prannoy Mehta
Q1.In school, we were learning about the magnetic properties of solids, and my teacher mentioned this, a spinning electrons create magnetic field. I cannot understand how. Like earlier we were told if a charge is in motion, it creates magnetic field, but in spinning, it does not have translation. It's in one place. I would like to add this as a question, a wire of current I is moving in +y axis and a electron is revolving at a distance of x m along +k direction, does it feel any magnetic force, and what if it was spinning along +y direction.

Q2.Why are magnets always in dipoles, and further, why magnetic fields form closed loops, while electric fields are open loops.

Thanks in advance for clearing the doubts.

Prannoy Mehta said:
Q1.In school, we were learning about the magnetic properties of solids, and my teacher mentioned this, a spinning electrons create magnetic field. I cannot understand how. Like earlier we were told if a charge is in motion, it creates magnetic field, but in spinning, it does not have translation. It's in one place. I would like to add this as a question, a wire of current I is moving in +y axis and a electron is revolving at a distance of x m along +k direction, does it feel any magnetic force, and what if it was spinning along +y direction.

Q2.Why are magnets always in dipoles, and further, why magnetic fields form closed loops, while electric fields are open loops.

Thanks in advance for clearing the doubts.
For first question, I think it is found by experiment, I don't know the answer.
For question 2, think of a magnetic dipole, the B flux in between N and S is from S to N, but for the flux going outside, will go from N to S, but for electric dipole, the flux always go from + to -. This tells you why magnet is closed loops and electric field is open loops.

Prannoy Mehta said:
I would like to add this as a question, a wire of current I is moving in +y axis and a electron is revolving at a distance of x m along +k direction, does it feel any magnetic force, and what if it was spinning along +y direction.
Thanks in advance for clearing the doubts.
the electron will not feel magnetic force if the electron perfectly follow the path. However, any little deviation will cost the electron to move down and up because of magnetic force, but this should not be a concern in your question.

Prannoy Mehta said:
Q2.Why are magnets always in dipoles, and further, why magnetic fields form closed loops, while electric fields are open loops.

An electric charge is a source of the electric field; Gauss's Law. $\rho = \epsilon \nabla \cdot E$. Gauss's Law for magnetims says $0= \nabla \cdot B$. This says, the divergence of the magnetic field is zero out of any region.

This doesn't say a lot. But if the electric and magnetic fields are expressed in terms of a more fundamental vector quantity $A$, where $B= \nabla \times A$, then it is a mathematical identity that $\nabla \cdot B$ must be zero. $\nabla \cdot \nabla \times A=0$ for any $A$.

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Prannoy Mehta
A1. Electron spin is a relativistic quantum mechanical effect which isn't actually an electron spinning in the classical sense. If you haven't studied quantum mechanics, there's no easy way to understand it, so you are just going to have to accept it. Anyways, the relativistic version of the Schrodinger equation for spin 1/2 particles (like electrons) is the Dirac equation. The Dirac equation predicts this effect known as spin and also how it couples to the magnetic field.
http://lnu.se/polopoly_fs/1.96725!PresentationGfactor.pdf
A1b. The loop of wire creates a magnetic field which has a torque on the electron, but not a force unless the electron is moving.

A2. It's because magnetic monopoles don't exist (or we haven't found them yet!). On the other hand, electric monopoles are common. A monopole is a place where field lines are converging or diverging from a point. Dipoles just form loops in the field.

Prannoy Mehta
stedwards said:
An electric charge is a source of the electric field; Gauss's Law. $\rho = \epsilon \nabla \cdot E$. Gauss's Law for magnetims says $0= \nabla \cdot B$. This says, the divergence of the magnetic field is zero out of any region.
using gauss's law to explain is circular argument. Gauss's law for B-field is based on the phenomenon. you cannot use the product of the phenomenon to explain.

sunmaggot said:
using gauss's law to explain is circular argument. Gauss's law for B-field is based on the phenomenon. you cannot use the product of the phenomenon to explain.

What circle? Anyway, I hit the wrong button and posted early. See the edited version of my post.

stedwards said:
What circle? Anyway, I hit the wrong button and posted early. See the edited version of my post.
circular argument: A is correct and implies B is correct. Why is A true? if you use B to prove A is correct, this is circular argument.

To summaggot: stedwards's answer is based on the theory of electromagnetism. It's not proven. Just not yet disproven. Circular arguments are acceptable to some extent in inductive reasoning. We (humans) created this theory of electromagnetism based on a lot of experiments. So when someone asks a question about why something happens in electromagnetism, it is sometimes better to answer in terms of the basic principles of the theory, rather than the experiments it rests on. Why? Well, the theory ties together a lot of measurements with a small number of assumptions. So the theory can be regarded as "explaining" the experiments, although the experiments are what imply the theory is correct. That's not circular. That's just how physics works.

sunmaggot
sunmaggot said:
circular argument: A is correct and implies B is correct. Why is A true? if you use B to prove A is correct, this is circular argument.

You didn't reread. Maybe you'll understand this better.

If there exists an R4 fibre bundle A on the spacetime manifold of general relativity, ddA=0 (all exact forms are closed) this precludes the existence of magnetic monopoles as a mathematical identity.

No, I have not gone through quantum mechanics with the dept prescribed, in the text give to me by Khashidi. But I don't get one part, it experiences torque but not force. o.o Does not make sense to be. I am ignoring the electrostatic forces.

But just wanted to know, the school provided text states, if we pick a reference frame as such to travel at the same speed as the electron near a current carrying conducting wire, there will be only a electrostatic force, despite the wire being neutral. These things, are weird. I cannot seem to understand these things, mechanics was much easier to understand.

But the wire isn't neutral from the electron's rest frame. With mechanics, you can often ignore relativistic effects if you are working with slow moving bodies. But electromagnetism and relativity go together, and you can't often ignore the effects of relativity.

## What is magnetism?

Magnetism is a phenomenon that results from the force exerted by moving electric charges, typically electrons, which creates a magnetic field. This field can attract or repel other magnetic materials.

## How do magnets work?

Magnets work by aligning the magnetic fields of the atoms within the material. In a magnet, the atoms are arranged in a way that creates a strong and consistent magnetic field. This field can then interact with other magnetic materials, causing attractive or repulsive forces.

## What is the relationship between electricity and magnetism?

The relationship between electricity and magnetism is known as electromagnetism. This theory states that electric fields and magnetic fields are intertwined and can create each other. Moving electric charges, such as electrons, create magnetic fields, and changing magnetic fields can induce electric currents.

## How do electrons play a role in magnetism?

Electrons are the key players in magnetism. They have a property called spin, which creates a tiny magnetic field around each electron. When many electrons are aligned in the same direction, their magnetic fields add up, creating a larger magnetic field. This is how magnets are able to attract or repel other objects.

## Why do some materials attract to magnets while others do not?

The ability of a material to be attracted to a magnet depends on its atomic structure. Materials with unpaired electrons, such as iron, nickel, and cobalt, are more likely to be attracted to magnets because their electrons are able to align and create a strong magnetic field. Other materials, such as copper and aluminum, have all their electrons paired and do not have a strong magnetic field, so they are not attracted to magnets.

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