Purpose: To investigate electrical charge, the production of electrical charge,
ID: 1534525 • Letter: P
Question
Purpose: To investigate electrical charge, the production of electrical charge, and how electrical charged objects interact with each other.
Apparatus: Scotch tape, wood meter stick, thread or hair
To aid in our understanding of electrical charges and their interaction, we are going to use “invisible tape”, such as Scotchâ brand MagicTM Tape.
Activity 1 - Initial observations of a U tape
Take a piece of tape about 20 cm long and fold over (a couple of cm) one end of the strip to make a non-sticky handle. Stick this piece of tape onto the top of your desk, smoothing
Tape handle – end folded
(Sticky side down) over
down this tape with your thumb or fingertips. This “base tape” provides a standard surface to work from.
Stick another 20 cm long piece of tape with a handle on top of the base tape and smooth with your thumb or fingertips. Write “U” on the top tape to represent the “upper” tape. With a quick motion, pull the U tape off the base tape leaving the base tape stuck to the desk.
1. Hang the U tape from a horizontal meter stick and bring the back of your hand near the hanging U tape.
(a) Briefly describe what happens.
(b) Does it matter which side of the tape you approach?
(c) Take another object, like a pen, and bring it near the hanging U tape. What happens to the U tape? Is this similar to what happened when you brought your hand near the U tape?
If the U tape is “good” and the room is not too humid, you should find that there is an attraction between the tape and your hand when you get close to either side of the tape. If not, try again.
(d) It is important, as you perform the activity above, that you keep your hands and other objects away from the tapes. Explain why his precaution is necessary.
Prediction:
If you prepare 2 U tapes and bring them near each other (but not touching), what do you expect them to do to each other?
(e) attract repel no interaction
(f) Give your reasoning.
Activity:
2. Now prepare a second U tape the same way you prepared the first. Now carefully bring the second U tape toward the hanging first U tape. (Try to keep your hands from being in between the 2 U tapes).
(g) Describe what happens.
You should find that the two U tapes repel each other rather strongly. If not, try again. After observing the repulsion, hang the second U tape besides the first.
Is there an electric interaction between U tapes?
To decide whether the interaction between two U tapes is or is not an electric interaction, we will see if it obeys the criteria for an electric interaction. The electric force between two charged objects is stated as being in the direction of a line drawn from one charged object to the other charged object.
Activity 2 - Electric Interaction between U tapes
3. Suspend a U tape from a thread or a hair. Hold the thread or hair in your hand, or use a short piece of tape to stick the upper end of the thread or hair to the meterstick. Approach the suspended tape from various directions with another U-tape. Do you find that the force does indeed act along a line drawn from one object to the other?
Summary: Forces act along a line connecting the charged objects!
4. Move a U tape very slowly toward another hanging U tape. Observe the deflections of the tapes from the vertical, at several distances (for example the distance at which you first see repulsion, half that distance, etc.) Make a very rough graph of the strength of the repulsive interaction as a function of the distance between the two tapes (you can’t really go all the way to zero distance!).
Strength of
force
0
Distance
The deflections of the tapes away from the vertical is a measure of the strength of the interaction. Does the force decrease rapidly as the distance between the tapes increases?
Summary: Force decreases rapidly as the distance between the tapes increases!
You may have already discovered that if you handle a U tape too much, it no longer repels another U tape. Next, we will learn a systematic way for making this happen.
5. Make sure that you have an active U tape, by seeing that it is attracted to your hand. Then, holding onto the bottom of the U tape, slowly rub your fingers or thumb back and forth along the slick side of the tape. Describe the changes in how this U tape no longer interacts with your hand.
You should find that the U tape no longer interacts with your hand, so we have a way of making a tape not interact with other ordinary objects, which will be useful in the future. If the U tape was electrically charged as we suppose (presumably on its sticky side), then by running a finger along the slick side we have apparently “neutralized” it – it now appears electrically neutral (uncharged).
6. Let’s partially neutralize a U tape and see what happens. Prepare two charged U tapes.
Hang one of them from the meterstick, and note how strongly the other tape repels it.
Partially neutralize one of the tapes by running your finger along the length of the slick side of the tape, being careful that your finger touches only a portion of the width of the tape.
Again observe how strongly the two tapes repel. What is the effect of this partial neutralization?
You should observe that the two tapes repel less strongly when you partially neutralize one of them. For now, you can see that to a certain extent we can control the amount of “charge” on a tape, and that the force between two tapes seems to depend on the amount of charge on each tape.
There are two types of charges that appear in nature. How could you prepare a tape that might have an electrical charge unlike the charge of a U tape?
Perhaps you reasoned along these lines: We don’t know how the U tape became charged, but if the tapes started off neutral, maybe the U tape pulled some charged particles off of the bottom tape (or vice versa). So, now the bottom tape might have an equal amount of charge, of the opposite sign.
Activity 3 - Making a “L” tape and observing interactions between a L and U tape
Stick a strip of tape with a handle down onto a base tape. Smooth this tape down with your thumb or fingertips. Write L (for Lower) on the handle of this tape. Stick another strip with a handle on top of the L tape, smooth it down, and write U on its handle.
Slowly lift the L tape, bringing the U tape along with it (and leaving the bottom base tape stuck to the desk). Hand the double layer of tape vertically from the edge of the meterstick and see whether there is attraction between it and your hand. If so, get rid of these interactions by rubbing the slick sides of the tape with your finger. We want the pair of tapes to be neutral.
Hold onto the bottom tab of the L tape and quickly pull the U tape up and off. Hand the U tape vertically from the edge of the meterstick, not too close to the L tape.
Repeating the above steps, make another pair of tapes so that you have at least two U tapes and two L tapes. Before separating the tapes from each other, remember to run your finger along the slick side of the tape pair to get rid of interactions.
If an L tape is indeed electrically charged, and its charge is unlike the charge on a U tape, what interaction would you predict between an L tape and a U tape?
Prediction: attraction repulsion no interaction
Reason:
7. Make sure both the U tape and L tape are active. What interaction do you observe between the L tape and U tape?
What interaction would you predict between two L tapes?
Prediction: attraction repulsion no interaction
Reason:
What interaction do you observe between the two L tapes?
Summarize the interactions you have observed between U and L tapes:
L-U Interaction U-U Interaction L-L Interaction
Is this pattern of interactions consistent with the statement “Like charges repel and unlike charges attract”?
If U and L tapes are electrically charged, then we would expect the strength of the attractive interaction to decrease as the distance between the tapes increase.
8. Move a U tape very slowly toward a hanging L tape. Observe the deflections of the tapes from the vertical, at several distances (for example the distance at which you first see attraction, half that distance, etc.) Make a very rough graph of the strength of the attractive interaction as a function of the distance between the two tapes (you can’t really go all the way to zero distance!). The deflection of the tape away from its original vertical position is a measure of the interaction.
Strength of
force
0 Distance
Why is this task more difficult with a U and an L tape than with two U tapes?
Do the forces between U and L tapes lie along the line between the tapes? Circle the description that matches your observations.
Force by U tape on L tape: Force by L tape on U tape:
along line between tapes along line between tapes
at angle to line between tapes at angle to line between tapes
Finally, what can you conclude about the U and L tapes as far as being electrically charge and what kind of charge each has?
*Based on a set of activities developed by Ruth Chabay and Bruce Sherwood.
Finally, what can you conclude about the U and L tapes as far as being electrically charge and what kind of charge each has?
*Based on a set of activities developed by Ruth Chabay and Bruce Sherwood.
Explanation / Answer
1. Hang the U tape from a horizontal meter stick and bring the back of your hand near the hanging U tape.
(a) Briefly describe what happens.
Here as we put our hand closer to the tape there is electrostatic interaction between hand and tape
and the tape will attract
(b) Does it matter which side of the tape you approach?
No the direction will not matter here as the induction matters only on the distance not on the direction
(c) Take another object, like a pen, and bring it near the hanging U tape. What happens to the U tape? Is this similar to what happened when you brought your hand near the U tape?
when we bring a pen of other object near to it and then when we bring hand near it than due to opposite force of the object or pen our inetrection with hand becomes weaker
If the U tape is “good” and the room is not too humid, you should find that there is an attraction between the tape and your hand when you get close to either side of the tape. If not, try again.
(d) It is important, as you perform the activity above, that you keep your hands and other objects away from the tapes. Explain why his precaution is necessary.
precaution is needed because if we touch the two objects then the charge will distribute and the force will change so we need not to touch the tape
Prediction:
If you prepare 2 U tapes and bring them near each other (but not touching), what do you expect them to do to each other?
(e) attract repel no interaction
We expect ATTRACTION
(f) Give your reasoning.
since this is due to the induction process so all charges are induced is of opposite nature
so this is always attraction
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.