Charging BY induction
Charging a Body: We know that all bodies are made of atoms/molecules which contains both positive and negative charge. In general the bodies are electrically neutral which means that the amount of positive or negative charge present in the body is exactly equal. To charge any body two methods can be used [a] Charging by conduction [b] Charging by induction Charging by conduction: In charging by conduction, the boy which is to be charged is placed in physical contact with some other body. This can be done in two ways [a] charging by contact [b] charging by friction Charging by contact: In charging by contact, a neutral body is placed in contact with the charged body. Charge is transferred from charged body to the uncharged body till some equilibrium condition is achieved [equilibrium condition is the common potential]. For e.g. if a positively charged body A is placed in contact with the neutral body B, electrons will be transferred from the neutral body to the charged body till both acquire a common potential. This concept is analogous to the transfer of heat between two bodies at different temperature, heat transfer takes place till a common temperature is acquired. This phenomenon can be used in case of bodies which conduct. Charging by friction: we know that in an atom the inner electron are tightly packed an outer electrons are comparatively loosely bound. Thus, lesser energy is required to free electrons in the valence shell of the atom. When we run to two bodies the work which we do in rubbing removes the electrons from the valence shell of atoms in body in which they are loosely bound. These free electrons are transferred to the other body. The body which gains electrons acquires negative charge and the body which looses electrons acquires positive charge. The net charge on this system remains same. For e.g. if we rub our shoes on a carpet our body gets charged, thus if we touch a metallic door handle the charge is transferred to handle and we experience a shock. Charging by induction: The phenomenon in which the body gets charged without placing it in direct contact with any other charged body is called charging by induction. As shown in figure two neutral metal spheres are in contact, both supported on insulating stands. When a negatively charged rod is brought near one of the spheres but without touching it, as in [b], the free electrons from the metal are repelled and drift slightly away from the rod, towards the right. This leaves a positive charge on the left sphere. This negative charge on right sphere and positive charge on left sphere are called induced charges. These induced charges remain on the surfaces of the sphere as long as the rod is held nearby. [When the rod is removed , the electron cloud in right moves to the left and original neutral condition is restored.] But suppose the electrons are separated slightly as shown in [c] while the plastic rod is nearby. If the rod is now removed the opposite charges on two spheres will attract each other. When the two spheres are separated by large distance each of the two spheres will have uniform
