# Tagged Questions

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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### How do permanent magnets manage to focus field on one side?

The actuator of a hard drive head consists of two very strong neodymium magnets, with an electromagnetic coil between them. If you take that apart, the magnets attract each other very strongly. There'...
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### Why does a ring falling through a magnetic field experience an upward force?

The Problem states: A metallic ring of Mass $M$ and radius $r$ falls freely under the influence of gravity in the direction along the negative Z-axis. A magnetic field $B_z = B_0(1-z\lambda)$ ...
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### Electromagnetic field and continuous and differentiable vector fields

We have notions of derivative for a continuous and differentiable vector fields. The operations like curl,divergence etc. have well defined precise notions for these fields. We know electrostatic and ...
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### Why is there a photon every millimeter on earth coming from a star millions of light years away?

I've been having this confusing thought for so long now it would be amazing if someone could answer me. Imagine this asterisk * . As you see, from the center point, lines go outwards, just like a ...
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### Does Faraday cage block magnetic field?

I want to block magnetic field of the very strong magnet, can I put it inside faraday cage to block its magnetic field?
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### Do neutron stars reflect light?

The setup is very simple: you have a regular ($1.35$ to $2$ solar masses) evolved neutron star, and you shine plane electromagnetic waves on it with given $\lambda$. Very roughly, what shall be the ...
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### If you run an electric current through a wire loop, do the accelerated charges radiate?

Does an accelerated charge always radiate? For example the current electrons in an electric circuit when moving through a turn they are accelerated, do they radiate because of that acceleration? If ...
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### Can I levitate an object without using an electromagnet?

I know that it's possible to make an object levitate using an electromagnet to hold it up. But is it also possible to do this with regular magnets? Is there a special kind of magnet I need in order ...
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### Apparent violation of Newton's 3rd law and the conservation of angular momentum for a pair of charged particles interacting magnetically

Consider a system of the two identical point positive charges situated in free space (isolated from influence of any other external fields) as shown in the figure below. Particle 1 is at $(a,a,0)$ and ...
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### Is the uniqueness theorem correct in superconductivity?

There is an uniqueness theorem in electromagnetism. It says that the solution of Maxwell's Equations is determined uniquely by boundary conditions. We can treat superconductivity as a completely ...
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### Can a third type of electrical charge exist?

Upon reading my book on physics, it mentions that there are only two discovered types of electric charges. I wonder if there could be a third type of elusive charge, and what type of effects could it ...
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### In electrostatics, why the electric field inside a conductor is zero?

In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero. I ...
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### Radio antennas that are much shorter than the wavelength

From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall ...
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### Is the magnetic field of a white-dwarf merely residual?

Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures? Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ...
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### How do electrons know when a circuit is closed?

I was told that electrons do not begin flowing unless the circuit is closed. The electrons from the battery are not in the ends of wire when it is open, apparently, as there is no reason for them to ...