Question

Describe some experiment to show that the magnetic field is associated with an electric current. 

Answer 1

We take a thick insulated wire and fix it in north-south direction. Now, we place a plotting compass under the wire. The two ends of the wire are connected to a battery through a switch.
Initially, let us fix the compass needle parallel to the wire, i.e., north-south direction, if no current is flowing through the wire. If we pass a current through the wire by pressing the switch, we observe that the compass needle gets deflected from its north-south position. Again, if current is switched off, the compass needle returns to its original position.
In this experiment, the deflection of compass needle by a current-carrying wire shows that an electric current produces a magnetic field around it. In other words, a magnetic field is associated with an electric current.