1A) One lab partner negatively charges a plastic rod by rubbing it with wool 2B)

Question

1A) One lab partner negatively charges a plastic rod by rubbing it with wool
2B) The rod is brought near a pith ball but not so close that they touch
1C)The pith ball is touched by another lab partner on the side opposite the charged rod
1D)The pith ball touches the plastic rod

Complete the table for the four steps of the lab experiment. You may use phrases or pictures instead of complete sentences

How did the pith ball react?___________________________ What did the electrons do?

A)_________________________________________________ A)



B)_________________________________________________ B)


C) _________________________________________________C)


D)_________________________________________________ D)

Explanation / Answer

Step A)

Nothing happens to the pith ball in this step. Only the plastic rod is being charged. The pith ball remains neutral in terms of its charge.

Step B)

As the rod is brought close to the pith ball, the ball tends to polarize. The electrons that are already on the pith ball balance the protons, because of its neutrality, but the electrons move away from the charged rod due the repulsive forces between like charges. So the side closest to the rod appears more positive and the side farthest from the rod appears more negative, but the total charge is still zero,

Step C)

Since the opposite side of the ball appears more negative, that side of the ball believes itself to have an extra amount of electrons. If your lab partner touches that side, the electrons on that side are "grounded" by your partner, and leave the ball. The ball, now, has a net positive charge because some of the electrons left.

Step D)

When the ball touches the rod, some electrons will leave the rod and end up on the ball so that the charge between them is equal. Most likely, the ball and the rod will have a net negative charge after the contact.

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