Electromagnetism is the study of magnetic effects of current. The use of electromagnetism in different fields of science and technology is very wide. Motors and electric meters are based on the effect of magnetism produced by the electric current in wires. Generators produce electric current due to the movement of wires near very large magnets.
15.1 MAGNETIC EFFECTS OF A STEADY CURRENT
Ampere discovered that when a current passes through a conductor, it produces magnetic field around it. To demonstrate this, we take a straight conductor wire and pass it vertically through a cardboard (Fig.15.1- a). Now connect the two ends of the conductor wire with the terminals of the battery so that current flows through the circuit in the clockwise direction. The lines of force of the magnetic field produced around the wire would be in the form of concentric circles. If we place a compass needle at different points in the region of magnetic field, it will align along the direction of magnetic field. Also if we sprinkle some iron filings on the cardboard around the wire, they will align themselves in concentric circles in the clockwise direction.
If we reverse the direction of the current by reversing the terminals of the battery, the compass needle also reverses its direction. Now the magnetic field lines will align in the anticlockwise direction (Fig.15.1- b). The magnetic field produced is stronger near the current- carrying conductor and weaker farther away from it.
Direction of magnetic field
The direction of the magnetic field is governed by the direction of the current flowing through the conductor. A simple method of finding the direction of magnetic field around the conductor is the Right Hand Grip Rule.