TESTING THE CHARGES

Bring a body under test near the disc of an uncharged electroscope. If the leaves remain parallel the body is neutral. The leaves will be diverge if the body has got charge on it. This shows the presence of charges on the body.

To examine the nature of charge, we have to put a known type of charges on the electroscope. It can be done by conduction or by induction. To charge by conduction, the disk is touched by hand so that the leaves collapse completely (if there were any charges). Then the disk is touched by an ebonite rod rubbed with fur. The charges on the rod will be transferred to leaves of electroscope and they diverge. The rod is removed and electroscope is negatively charged. If similar process is carried out with glass rod rubbed with fur. The charges on the rod will be transferred to the leaves of electroscope and they diverge. The rod is removed and electroscope is negatively charged. If similar process is carried out with glass rod rubbed with silk the electroscope will be positively charged.

Charge it by induction one should follow the procedures described in section 5 of this chapter. First touch the disk of the electroscope by hand and the leaves will collapse. Remove the hand. Bring a glass rod rubbed with silk near the disc. The leaves will be diverging. Keeping the rod there ground the disc on the opposite sides. The leaves will collapse. Disconnect the ground first and then remove the glass rod. Again the leaves will diverge and the electroscope will be negatively charged. The same process is carried out with an ebonite rob rubbed by fur to charge the electroscope positively.

After charging the electroscope the body under the test is brought near the disc of the electroscope. If the electroscope was negatively charged and leaves diverge more then the body is negatively charged. But if the divergence diminishes, the body is either positively charged or simply uncharged i.e. neutral. To make sure the disc is touched by hand to make the leaves collapse. Then the body is brought near the disc. If the leaves diverge the body possesses positively charged and if the leaves are unaffected the body is electrically neutral.

It should be clear that attraction does not always confirm the presence of charge, but repulsion does.