Question

Why only does a coiled wire and not a straight wire in an electical circuit behave like a magnet?

Answer 1

An inductor is something that fights changes in currents, or mathematically speaking di/dt.
And it fights it by producing a back emf, an emf which always opposes the di/dt.

And how much it fights depends upon what is called as the inductance of the inductor. Now of the many things the inductance depends upon, one of them is the number of turns or number of coils.

Now if you use a straight wire, you might say, there is no turn or a coil and thus inductance would be zero. And thus there is no fighting to the di/dt, which means current must instantaneously change. So when you switch on the battery of the circuit, current must instantly go from zero to max. But you know this in your bones, that this cannot happen. It would need some finite time right? That means there must be some inductance. But how?

Well, a closed electrical circuit IS A LOOP right? you can never have a circuit without having ATLEAST one loop. So that one loop will provide small inductance.
But if you make a lot of turns,then obviously inductance would increase.