Effect of a charged rod on a charged gold-leaf electroscope
On page 364 it was shown how a gold-leaf electroscope can be used to test the sign of the charge on a body. It will be remembered that a charge of the same kind as that on the electroscope causes an increase, while a charge of opposite kind causes a decrease in leaf divergence. We are now able to explain this in terms of the electron theory.
Fig. 32.10, which is self-explanatory, gives the reason for the increased divergence in the case where both charges are negative. The diagram and explanation for the positive case are left as an exercise.