Arturo O. answered • 11/10/17
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When the positive object is brought near the top, negative charges migrate from the gold leaves to the top, since the negative charges in the gold (which is a conductor that has electrons that can move about) are attracted by the positive charge. That leaves behind a net positive charge on the leaves, even though the scope remains neutral overall. Hence, the leaves repel each other and move apart. When a finger touches the top of the scope while the positive object remains near the top, it basically grounds the scope, meaning that the net positive charge in the leaves flows to the ground through the finger. But the positive object continues to "hold" negative charges in place at the top. The leaves have lost their net positive charge, so they no longer repel, and they move closer together. If the positive object is moved away, the negative charges at the top are no longer attracted to the top, and they redistribute themselves throughout the electroscope, moving into the leaves and charging them negatively. Hence, the leaves move apart from each other again. You now have a negatively charged electroscope. If you now bring a negatively charged object close to the top, but without touching, the negative charges already in the scope will be repelled down toward the leaves, making them more negative, causing them to repel more, and hence move even farther apart. You end with the situation described by answer (B).
