Static Electricity Lab

 Materials: Everyday household items such as plastic straw, paper bits, styrofoam coffee cup, wool or fur Time Allotment: 4 Class Days

Purpose:

The purpose of this activity is to study different charge interactions between objects and to draw some generalizations about the attractive and repulsive nature of these interactions.

Part A: Electrical Interactions

Materials: plastic straw, paper bits, styrofoam coffee cup, wool (as in a wool sweater or wool blanket)

1. Tear part of a piece of paper into small bits. Take a plastic drinking straw and bring it close to the bits of paper. Can you lift the bits of paper by touching them with the straw? ___________

2. Now rub the straw briskly with fur or wool or against your hair and try to lift the bits of paper from the table. Can the scraps of paper be lifted even if you do not allow the rubbed straw to touch them first? ___________

3. Repeat this using the styrofoam coffee cup, trying to lift the paper bits before and after rubbing the cup on wool, fur or your hair. What are your results with the cup?

4. Apparently, after the straw has been rubbed there is an interaction between the straw and paper which is capable of lifting the scraps of paper. What can you say about the size (smaller.larger or the same size) of this interaction force compared to that of the earth's gravitational interaction force with the scraps of paper? ______________ Explain.

5. DEFINITION: The force involved in this interaction is called an electrical force, and was first observed by the Greeks, who found that pieces of amber (in Greek, elektron) attracted other things after being rubbed with fur. Materials which are capable of attracting the bits of paper are said to be electrically charged.

6. Is the styrofoam cup electrically charged according to the definition given in #5? ______ Explain.

7. Are the bits of paper charged according to the definition given in #5? ______
• Devise and perform an mini-experiment to determine whether the paper is charged. Describe the procedure of your mini-experiment.

Part B: Interaction Between Charged and Uncharged Objects

Materials: Scotch magic tape, paper bits, sheet of paper.

1. Obtain about 15 cm of the Scotch tape and make tabs by folding the first centimeter of tape on each end, sticky side together. Stick the tape to the table-top and press and rub it down well with your finger. Now peel the tape carefully but briskly from the table top.

2. Will either or both sides of the tape attract the scraps of paper? __________ Explain what happens.

3. Does the tape meet the definition of being charged (see definition in Part A)? __________ Explain.

4. Roll a piece of paper into a tube and bring it near the tape. Is there an interaction between the paper and the tape? _________ What type of interaction (attractive or repulsive) is it?

5. In Part A, a definition was given for an object being charge. Does the paper tube meet your definition of being charged? ________ Explain why or why not.

Part C: Interaction Between Two Charged Objects

Materials: Scotch magic tape.

1. Make a second tape strip like the first one. Press them both down on the table separately, and then peel them loose from the table. Try bringing the tapes near each other. What effect (attract, repel or no interaction) do they have on each other? ____________________ Does it matter which sides of the tape face each other?

2. Make a third strip of tape, charge it and try bringing it close to each of the other two tapes. Compare one of yours with those of another student, or stick their ends to something so that you have enough hands. What do you observe?

3. REVISED DEFINITION: In Part A, a definition was given for an object being charge. Here we have found that the definition is not quite complete. Based on these observations, extend your definition of an object which is electrically charged.

Part D: Do All Charged Objects Behave the Same Way?

Materials: plastic straw, Scotch magic tape, styrofoam cup.

1. Tape a straw to the top of your desk or table so that about three-fourths of the straw sticks out over the floor.

2. Charge another 15-cm tape by sticking it to the table top, rubbing the tape, and peeling the tape from the table. Hang this charged tape from the end of the straw by sticking the tape to the straw. This is a test tape.

3. Make two new tape strips in the following manner. Label the first one A, press it down on the table, and rub it with your finger. Label the second one B, press it firmly down on top of A, and rub it with your finger. Peel the two-tape combination off the table. Bring them near the test tape. What do you observe?

4. Bring the combination near some paper bits. What do you observe (attraction, repulsion or no interaction)?
• Is the combination tape charged under either or both parts of your definition? Explain.

5. Carefully peel apart the two tapes. Hold one in each hand and bring them slowly towards each other.
6. Bring A towards the test tape.
• What do you observe (attraction, repulsion or no interaction)?

• Bring B toward the test tape. What do you observe (attraction, repulsion or no interaction)?

7. Are both A and B charged according to your definition of charged? ___________ Explain why or why not.

8. Devise a mini-experiment that will show convincingly that both A and B are charged according to your definition. Write down the steps of your mini-experiment and try it.

9. How does testing for charge by attraction compare to testing by repulsion in terms of their relative effectiveness as a test for an object being charged? Would either test alone be sufficient? ______ If so, which one and explain why. If not, explain why not. (This is an important question. Do a bang-up job.)

10. REVISED DEFINITION: The definition for an object begin charged was last revised in Part C. You now need a new definition for an object being charged. Revise your old definition and write it in the following space.

11. Tape another straw to your desktop with three-forths of the straw hanging over the floor like you did in #1. Hang tape A on the end of one straw and tape B on the end of the other straw. Try rubbing various objects including a straw and a foam cup against various materials and test them against tapes A and B. Conduct a sufficient number of tests in order to answer the following questions. Record your observations here:

12. Do all objects that repel A also attract B? __________ Do all objects that repel B also attract A? __________ Do any objects repel both A and B? __________ Do any objects attract both A and B? __________ Do these objects meet your definition of being charged? __________ Explain how you know.

Part E: Charges and Charged States

Materials: styrofoam picnic plate, fur or wool, and tape combination.

IMPORTANT: If two charged objects behave the same in their interactions with all other objects, we may describe them as being in the same charged condition or in the same charged state. We will suppose that a charged state depends on the presence of something called charge. With this hypothesis, we need to account for the charged states of A tapes, B tapes, and unrubbed paper in terms of the kind or kinds of charges present.

1. How do two A tapes interact (attract, repel or no interaction)? __________ How do two B tapes interact (attract, repel or no interaction)? _________

2. Based on your experiences would you say that the two A tapes have the same or different charge? _____________ Would you say that the two B tapes have the same or different charge? ________________

3. On the basis of these observations we now assume that A tapes have one kind of charge and B tapes have another. What is the interaction (attract, repel or no interaction) between two objects with the same kind of charge?

4. How does an A tape interact (attract, repel or no interaction) with a B tape? ________ Describe the interaction between two objects with different kinds of charge.

5. How do two bits of unrubbed paper interact?_________ If we were to assume that the behavior of unrubbed paper is due to the presence of a third charge, would the behavior of this third charge be consistent with the behavior of A and B? _________ Explain your answer.

6. How does an A tape interact (attract, repel or no interaction) with a B tape?

7. How does an A tape interact (attract, repel or no interaction) with paper bits?

8. How does a B tape interact (attract, repel or no interaction) with paper bits?

Conclusion:

1. Use complete and detailed sentences to describe the different types of interactions (attractive, repulsive or no interaction) which exist between positively charged, negatively charged, and neutral objects.

2. Describe what definitive observation (or set of observations) which would have to be made in order to determine whether or not an object is charged.