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