INSULATOR

It is the clear that the inducing charge of the body (rod) produces opposite type of induced charges. It should be noticed that the inducing charge on the glass rod does not change. We can charge many conductors by the same rod i.e. we can obtain limitless supply of electrical charge this way. By connecting positively charged and negatively charged bodies to a bulb we can desire electrical energy. Does this violate the principal of conservation of energy? Definitely not. In removing the inducing rod we must do some work against the attractive forces between the opposite charges on the rod and conductor.

The phenomenon of electrostatic induction allows us to understand the attraction between a charged body and a neutral body. Suppose a positively charged rod A is brought near a small metal sphere B suspended by a thread (fig.32.4). Instantly, free electrons in the sphere will move towards the side, which is near the rod A. The near side be negatively charged and the far side will be positively charged by induction (fig. 32.4) The induced negative charge will be attracted towards and the induced positive charge will be repelled away from the positive charge on A. But, since the induced negative charges on B are relatively closer than the induced positive charge on it, the force of attraction is greater than the repulsive force. So the net force on B will be attractive and the ball will be pulled towards the rod. Note that induction takes place first which result the attraction.

If we bring the a positively charged rod near a conductor ( insulator) the net force will be attractive but the force will be smaller than in the case of conductor. It is because there are no free electrons inside the insulator- all the electrons are bound to their respective atoms. Thus, the negatively charged particles (electrons) are an atom in C is drawn closer ton A than the nucleus. This type of displacement of negatively charged electrons and positively charged nucleus in an atom is called ‘electric polarization’. Insulation is also called dielectrics in this sense. First there is electric polarization and then there is attractive. We shall talk about it in detail later in chapter 35.