Magnetic effect of current
It was on 21st April 1820, Hans Christian Oersted, a Danish Physicist was giving a lecture. He was demonstrating electrical circuits in that class. He had to o en switch on and o the circuit during the lecture. Accidentally, he noticed the needle of the magnetic compass that was on the table. It deffected whenever he switched on and the current was owing through the wire. The compass needle moved only slightly, so that the audience didnâ€™t even notice. But it was clear to Oersted that something signi cant was happening. Intrigued, he conducted experiments to nd out a startling effect, the magnetic effect of current.
Oersted aligned a wire XY such that they were exactly along the North-South direction. He kept one magnetic compass above the wire at A and another under the wire at B. When the circuit was open and no current was owing through it, the needle of both the compass was pointing to north. Once the circuit was closed and electric current was owing, the needle at A pointed to east and the needle at B to the west as shown in Figure 3.9. is showed that current carrying conductor produces magnetic field around it.
The direction of the magnetic lines around a current carrying conductor can be easily understood using the right hand thumb rule. Hold the wire with four ngers of your right hand with thumbs-up position. If the direction of the current is towards the thumb then the magnetic lines curl in the same direction as your other four ngers as shown in Figure 3.10. is shows that the magnetic field is always perpendicular to the direction of current.
The strength of the magnetic field at a point due to current carrying wire depends on: (i) the current in the wire, (ii) distance of the point from the wire, (iii) the orientation of the point from the wire and (iv) the magnetic nature of the medium. The magnetic field lines are stronger near the current carrying wire and it diminishes as you go away from it. is is represented by drawing magnetic field lines closer together near the wire and farther away from the wire.