Suspend the metal cup from the plastic rod attached to the stand and connect it
ID: 1603593 • Letter: S
Question
Suspend the metal cup from the plastic rod attached to the stand and connect it as shown by means of a conducting wire to the knob of the electroscope. Use a proof plane to make a momentary connection between the knob and the grounded case (recall the ground wire, not shown thus "shorting out" and completely discharging the electroscope. Important: Place the electroscope as far away from the cup as the wire permits. Next, charge up the glass rod and hold it far away from both the electroscope and the cup. Now bring the glass rod closer to the cup, but not too close. (Do not let the rod touch the cup, or you know what may happen to the gold foil.) Observe the motion of the movable leaf. (a) What are the electrons doing in this case? (b) What would the electrons do if the wire were replaced by a dry string that does not conduct electricity? (Are you absolutely sure? How could you find out whether or not your answer is correct?)Explanation / Answer
a) In the first case, the leaves will repel each other as when glass rod is brought closer to cup, it gets charged due to induction, and those charge flow to leaves of electroscope and they repel as they have acquired same charge. The force of repulsion between electrons results in replusion.
b)if the wire is replaced by dry string, the metal cup will acuire opposite charges to that of glass rod and force of attraction will result between them
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