course
Considering the lack of the PVC pipe you did well on this experiment.
Experiment 21: Electrostatics
As demonstrated on the video clip, place two pieces of Scotch tape or equivalent back-to-back, then rapidly strip them apart.
• Convince yourself that the two pieces attract one another.
• Hang both pieces from the edge of a table (it might be necessary to extend a book or a board beyond the edge of the table so that the tape can hang freely without being attracted to the body of the table).
Charge the piece of PVC pipe by rubbing it vigorously against your clothing or a cloth.
I did not have the PVC pipe, so I used tape to get a similar reaction.
• Test whether the pipe attracts or repels each piece of tape. It was attracted.
• Keep track of the two pieces of tape so you know how each is affected by the pipe.
Strip two more pieces of tape in the same manner and bring one of them near each of the hanging strips, in turn.
• Pick one of the pieces and determine whether the charged pipe attracts or repels it.
• Predict whether this piece of tape will attract or repel each of the hanging pieces. Then observe, and note your results. I predict that the tape piece that I picked will be attracted to the other pieces of tape (PVC) pipe. The piece of tape was attracted that I picked.
• Predict whether the other piece of tape just stripped will be attracted to or repelled from the charged pipe, and from each of a hanging pieces, then test your prediction and note your results. I believe it will be attracted as well.
Now wrap a piece of aluminum foil around one end of the pipe, extending back about a foot from the end. Hold the other end and bring it near one of the pieces of hanging tape.
• Note the behavior of the tape, then predict what will happen when you bring the same end close to the other piece of hanging tape.
When I did this, the tape did not do anything because the foil was around the other strips of tape.
When you strip apart two pieces of tape and bring them near a third charged piece of tape, one will be attracted and the other repelled. If the third piece isn't charged by stripping it away from another piece of tape, then both of the first two pieces will appear to be attracted to it, which is due to a phenomenon called 'induced charge'.
However there are only two types of charge.
• Can the behavior you observe be explained by the existence of a third type of charge?
It most likely can, but I am a little confused on what the third type of charge is exactly, based on these observations.
Can you think of a test that would prove or disapprove the existence of a third type of charge?
• Explain what happened in terms of two types of charge. Because the surface of the aluminum foil is densely permeated with freely mobile electric charges, they will move in response to any net electrostatic field. The outside charge attracts opposite charges, which build to greatest density on regions of the aluminum cylinder nearest it. This process must continue until there is no electric field in the aluminum, because if there is an electric field in the aluminum then charges will move in response to it. Movement of charges must continue until the field is eliminated. This effectively 'shields' all point inside the cylinder from the effect of external charges.
Bring your finger close to one of the hanging pieces of tape, and determine whether your finger attracts or repels the tape.
• Predict whether your finger will attract or repel the other piece of tape, then test and note your results. I think that my finger will repel the piece of tape. My finger actually attracted the piece of tape.
Charge the PVC pipe again and test to be sure it either attracts or repels the hanging pieces of tape. Then place a sheet of aluminum foil near one of the hanging pieces, as close as possible without attracting the tape.
• Bring the PVC pipe (without the foil on the end) closer and closer to the tape, while keeping the foil between the pipe and the tape.
• How is the effect of the pipe on the tape different than if the aluminum foil is removed? Explain what is going on. The tape should be attracted because the aluminum is removed. The charges are not being shielded as explained before.
Make an aluminum cylinder at least 20 cm in diameter, and carefully surround one of the hanging pieces of tape with the cylinder.
• Bring the charged pipe (without the foil on the end) near the tape while keeping it outside the cylinder. Explain what happens. I would presume that they would not be attracted to each other.
Remove the aluminum foil from the end of the pipe, keeping it cylindrical. Place one end of the foil cylinder near the hanging tape which is repelled by the charged pipe, but not so near that it pulls the tape into contact.
• Charge the pipe, then bring it near the other end of the foil cylinder.
• Observe what happens to the hanging tape.
• Remove the foil cylinder and bring the charged pipe to the same point as before.
• Explain any difference in the behavior of the tape due to the aluminum cylinder.
I am not exactly sure what would happen.
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