CHARGING A CON DUCTOR BY INDUCTION

Take a metal rod (A.  conductor) AB mounted on an insulating stand as shown in figure 32.3. Bring a positively charged rod towards one end, say A, of the conductor without touching it (fig 32.3(a)).  The end A will develop negative charge and the end B will develop positive charge due to the electrostatic induction. The reason that is the free electrons in the conductor will be attracted towards the end A by positively charged rod and the same number of electrons will be deficient on the side B. End A will be negatively charged and end B will be positively charged.

Now if we connect the end B of the conductor to ground using the metal wire the positive charges will move to the ground. (fig.32.3 (B) (Actually, the electrons come from the ground to the conductor and neutralized those positive charge). But the induced negative charges near A remains there, because these charges are free to move.

Because the electrons at the end B have flown from earth, they are called free charge. The electrons near end A are not free to move. They are held by the inducing charges. Therefore, they are called bound charge.

Again, disconnect end B from the earth. The –ve charges will remain near the end A as before under the influence of the inducing charge (fig. 3©.

Finally if we remove the glass rod as well, the negative charge will spread over the surface over the surface of the conductor evenly and the conductor will become negatively charged (fig.3 (d)).

These are the steps to be followed to charge a conductor by the method of induction. In this activity we described methods to charge a conductor negatively. Exactly the same steps should be carried out to charge the conductor positively, with the difference that we should take a negatively charged rod in place of the glass rod above or connect end A to the ground in the previous activities.

It is a clear that the inducing charges of the body (rod) produce opposite type of induced charges. It should be noted 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 the electrical charge this way. By connecting positively charged and negatively charged bodies to the 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 same work against the attractive forces between the opposite charges on the rod and conductor.