Principles & Laws of Electro-Magnetism

Oersted's experiment: Oersted, a Danish scientist discovered in 1819 there is a close relationship between electricity and magnetism. He observed that when a magnetic needle is placed under and parallel to a conductor, and then the current switched on, the needle tends to deflect at right angles to the wire.                                    

Electromagnetism: On passing a current through a coil of wire, a magnetic field is set up around the coil. If a soft iron bar is placed in the coil of wire carrying the current, the iron bar becomes magnetized. This process is known as `electromagnetism'. The soft iron bar remains as a magnet as long as the current is flowing in the circuit. It loses its magnetism when the current is switched off from the coil. The polarity of this electromagnet depends upon the direction of the current flowing through it.                   

Electromagnetism in a wire:- A magnetic field is formed around a conductor carrying current. The field is so arranged around the conductor as to form a series of loops.                    

            

Right Hand Grip Rule :-The Right Hand Grip Rule can be used to determine the direction of the magnetic field. If you wrap your fingers around the wire with your thumb pointing in the direction of current flow, your fingers will point in the direction of the magnetic field.                   

Corkscrew rule:-Assume a right handed corkscrew to be along the wire so as to advance in the direction of the current. The motion of the handle gives the direction of magnetic lines of force around the conductor.                                           

If two wires carrying current in opposite directions are brought close to each other, their magnetic fields will oppose one another, since the flux lines are going in the opposite directions.                   

When wires carrying current in the same direction are brought together, their magnetic fields will aid one another, since the flux lines are going in the same direction. The flux lines join and form loops around both the wires, and the fields bring the wires together. The flux lines of both wires add to make a stronger magnetic field. Three or four wires put together in this way would make a still stronger field.

                 

Electromagnetism in a loop: : If the wire is made to form a loop, the magnetic fields around the wire will all be so arranged that they each flow into the loop on one side, and come out on the other side. In the centre of the loop, the flux lines are compressed to create a dense and strong field. This produces magnetic poles, with north on the side that the flux lines come out and south on the side that they go in.

                               

Electromagnetism in a coil: If a number of loops are wound in the same direction to form a coil, more fields will add to make the flux lines through the coil even more dense. The magnetic field through the coil becomes even stronger. The greater the number of loops, the stronger the magnetic field becomes.

                                               

A helical wound coil that is made to produce a strong magnetic field is called a solenoid.

The Right Hand Palm Rule : Hold the right hand palm over the solenoid in such a way the fingers point in the direction of current in the solenoid conductors then the thumb indicates the direction of magnetic field (North Pole) of the solenoid.