Electrical Engineering ⇒ Topic : Methods of Charging a Conductor

Methods of Charging a Conductor

An uncharged conductor can be charged by the following two methods :

(i) By conduction

(ii) By induction

(i) By conduction. In this method, a charged body is brought in contact with the uncharged conductor Fig.(i) shows the uncharged conductor B kept on an insulating stand.When the positively charged conductor A provided with insulating handle is touched with uncharged conductor B [See Fig.(ii)] free electrons from conductor B move to conductor A. As a result, there occurs a deficit of electrons in conductor B and it becomes positively charged. Similarly, if the conductor A is negatively charged, the conductor B will also get negatively charged.

                                                          FIGURE

It may be noted that conductor A is provided with an insulting handle so that its charge does not escape to the ground through our body. For the same reason, the conductor B is kept on the insulating stand.

(II)By Induction. In this method, a charged body is brought close to the uncharged conductor but does not touch it. Fig. (i) shows a negatively charged plastic rod (provided with insulating handle) kept near an uncharged metal sphere. The free electrons of the sphere near the rod are repelled to the farther end. As a result, the region of the sphere near the rod becomes positively charged and the farthest end of sphere becomes equally negatively charged. If now the sphere is connected to the ground through a wire as shown in Fig. (ii), its free electrons at the farther end flow to the ground. On removing the wire to the ground [See Fig.(iii)], the positive charge at the near end of sphere remains held there due to the attractive force of external negative charge. Finally, when the plastic rod is removed [See Fig. 5.2 (iv)], the positive charge spreads uniformly on the sphere. Thus, the sphere is positively charged by induction. Note that in the process, the negatively charged plastic rod loses none of its negative charge. Similarly, the metal sphere can be negatively charged by bringing a positively charged rod near it.

                                           (iii)                                                                                            (iv)

Note that charging a body by induction requires no contact with the body inducing the charge. This is in contrast to charging a body by conduction which does require contact between the two bodies