Why is the magnetic field induced by an electric current in a straight wire in the form of concentric circles around the wire?


Why is the magnetic field induced by an electric current in a straight wire in the form of concentric circles around the wire?

In: 13

The “why” of the right hand rule requires us to know why the universe was created the way it was, why quarks are quarks etc, a level of knowledge we cannot answer. We only observe.

For more explanation of Fleming’s right-hand rule, and the laws that electromagnetism and charges seem to obey:

Magnetism and electricity are both a part of electromagnetism. It is one of the four fundamental forces in the universe, the others are gravity, weak force, and strong force. The weak and strong force is important for the interaction between particles in the atomic nucleus and for the quarks in the protons and neutrons themself.

We do not know of a lower-level explanation for electromagnetism, there might not be one. So the best explanation we have is that is how electromagnetism works. It might be impossible to explain why it works that way in our universe.

So the best answer we have is that is how the universe works.

Physics is about asking how it happens not why it happens, Even if we have a lower-level explanation that can be in multiple levels it will always end up as that is how the universe works.

This is a bit of simplified ELI20 but if you try to calculate the interaction between two moving electrons and only factor in their electrostatic forces (if they weren’t moving) and relativistic effects, after calculating everything, the resulting force is the same electrostatic force plus the magnetic force. Literally magnetic forces are a consequence of moving electricity. So the answer is kinda that the magnetic fields are concentric circles because the electrostatic force is along the radiuses of those circles, aka the math checks out, it just is that way, which was the point of the other comments.

Magnetic fields are caused by moving electric charges (like electrons). (I’m not sure there’s an ELI5 for this, it’s just the way it is). But, in order to conserve energy, the magnetic field can’t be in the direction of the motion of the electrons, because then the magnetic field would either speed up or slow down the electrons, causing “free” or “disappearing” energy. So it needs to be perpendicular to the flow. It can’t be crosswise to the wire because then it would have to choose a direction to cross it at (and classical physics equations don’t like to make up directions or amounts, they like to be predictable). So, the only other choice is around the wire, which is the only other “perpendicular direction” to the flow