Raheema Javed
Last Activity: 10 Years ago
Suppose that an electroscope carries a charge of unknown sign. Consider what happens when we bring a negatively charged amber rod, produced by rubbing the rod with fur, close to the knob of the electroscope. The excess electrons in the rod repel the free electrons in the knob and shaft of the electroscope. The repelled electrons move as far away from the rod as possible, ending up in the gold leaves. Thus, the charge on the leaves becomes more negative. If the original charge on the electroscope is negative then the magnitude of the charge on the leaves increases in the presence of the rod, and the leaves consequently move further apart. On the other hand, if the original charge on the electroscope is positive then the magnitude of the charge on the leaves decreases in the presence of the rod, and the leaves consequently move closer together. The general rule is that the deflection of the leaves increases when a charge of the same sign is brought close to the knob of the electroscope, and vice versa.