in Fig. AB is a conducting rod mounted on an insulating stand S. CD is a positively charged glass rod. When this rod is brought near the end A of rod AB the free electrons of the conducting rod are attracted towards the end A, hence this end acquires a negative charge. Now, due to deficiency of electrons at the end B it acquires an equal amount of positive charge. But as soon as the charged glass rod CD is carried away from AB the charges at the ends A and B disappear. Thus the electrification of rod AB is temporary.
“The phenomenon of temporary electrification of a conductor in which opposite charge appears at the closer end similar charge appears at the farther end under the influence of a charged body in its neighbourhood is called electrostatic induction.”
The positive and negative charges developed at the ends of the conducting rod are called induced charges and the charge on the glass rod which induces these charges on the conducting rod is called inducing charge.
Examples of Electrification by Induction
Electrification of a sphere by induction- Suppose we have to charge a metallic sphere with negative charge by electrostatic induction. For this we have to place the metallic sphere on an insulating stand. Now a positively charged rod is brought close to the uncharged metallic sphere without touching it, hence the free electrons of the sphere are attracted by the positive charge of the rod which accumulate at . the nearer edge of the sphere. Therefore this edge becomes negatively charged, and the farther edge of the Sphere becomes positively charged due to exit of free electrons from here [Fig]. The redistribution of charge is almost instantaneous and stops as soon as the net force on free electrons in the sphere becomes zero. At this stage the negative charge and positive charge deve10ped in the sphere are equal in magnitude.
Electrostatic Induction Special Notes
When natural body is taken near a charge is devloped on nearer surface and similar nature of charge is devloped on for surface of natural body. This phenomem is called Electrostatic Induction. When a charge body attracts a natural body, Before attraction, the phenomem of induction ta takes place.
There are two process by which natural body can be charged.
1: Induction Methods- In this methods natural body is kept near a charged body and for surface of natural body is connected with earth by a conducting wire. The charge devloped on for surface of natural body due to induction goes into earth and the charge devloped on nearer surface of natural body is distrubted in whole part of body in such a way natural body becomes charge.
2: Conduction Method- In this method charge body is to be taken in contact with natural body. Some amount of charge of charged body is to be transferd on natural body and in such a way natural body becomes charged. When both body are indentical then charge is share equally among them.