Name: ______Pd: ____ Date:______

Physics: Electrostatics Lab Background: Whenever two dissimilar materials are rubbed together, static electricity may be produced: one material acquires a positive charge and the other a negative charge. In this experiment, we shall produce charges, examine the properties of charged objects, and verify the basic laws of electrostatics.

Apparatus: Electroscope, pith ball, clear plastic rod, white PVC pipe, cotton cloth, and fur.

Procedure: Answer questions as they appear

1. Negatively charged “white pipe” a. Rub the white pipe with the fur to give the pipe a negative charge. Bring the pipe close to a neutral pith ball, but do not touch the pith ball. What happens to the pith ball? Why?

Draw the pipe as negative brought near the pith ball…draw what happens to the charge on the pith ball before you bring the rod close, during the time the rod is close and after the rod is removed. BEFORE: DURING: AFTER:

b. Explain why you think the pith ball, which is neutral, is attracted to the negatively charged pipe.

c. Now, charge the pipe again, and this time, touch the neutral pith ball gently with the pipe. What happens to the pith ball now? Why?

Draw the pipe as negative, touching the pith ball…draw what happens to the charge on the pith ball and pipe. BEFORE: DURING: AFTER:

2. Positively charged clear plastic rod. (Pay close attention, try, try again…this may not work as well—you have to make very careful observations.) a. Rub the clear plastic rod with the piece of cloth to make the rod positively charged. Bring the rod close to, but, do not touch the neutral pith ball. What happens to the pith ball? Why?

Draw the rod as positive brought near the pith ball…draw what happens to the charge on the pith ball. BEFORE: DURING: AFTER: b. Now, charge the clear rod again, and this time, touch the neutral pith ball gently with the positively charged rod. You may have to touch all “sides” of the pith ball. (Keep the pith ball charged for part c.) What happens to the pith ball? Why?

Draw the rod as positive, touching the pith ball…draw what happens to the charge on the pith ball and the rod. BEFORE: DURING: AFTER:

c. Now, charge the white pipe again with the fur “negatively”. Bring the negatively charged pipe close to the charged pith ball (from part b). What happens to the pith ball and why?

3. LIKE charges ______each other

UNLIKE charges ______each other

4. Charging an electroscope by CONDUCTION

a. Charge the white pipe negatively by rubbing it with fur. Touch the pipe to the top of the neutral electroscope. What is the charge of the electroscope? Why?

Draw the pipe as negative, touching the electroscope…draw what happens to the charge on the electroscope and pipe. BEFORE: DURING: AFTER:

b. Why do the leaves of the electroscope stay apart?

c. Touch the top of the electroscope (all “sides” of the small metal globe on top) gently with your fingers to neutralize it (called grounding).

d. Charge the plastic rod positively. Touch the plastic rod to the neutral electroscope. What charge does the electroscope have now? Why?

Draw the rod as positive, touching the electroscope…draw what happens to the charge on the electroscope and rod. BEFORE: DURING: AFTER:

e. Why do the leaves of the electroscope stay apart?

e. Neutralize the electroscope again. 5. Testing the charge on an object

a. Charge the white pipe negatively. Touch the electroscope. The electroscope is now negatively charged by conduction.

b. Charge the plastic rod positively. Bring the rod close to the charged electroscope (but do not touch). What happens to the leaves of the electroscope? Why?

c. Recharge the electroscope again with a negative charge by the white pipe. Bring the negatively charged pipe close to the negatively charged electroscope (but do not touch). What happens to the leaves of the electroscope? Why?

d. You can test the charge of an unknown object by bringing it close to a charged electroscope. Observe your results above and answer these questions.

If the electroscope and the unknown charged object are oppositely charged what happens to the electroscope’s leaves?

If the electroscope and the unknown charged object are the same charge what happens to the electroscope’s leaves?

6. Charging an electroscope TEMPORARILY BY INDUCTION

a. Charge the white pipe negatively. Bring the pipe close to the electroscope’s top, but do not touch. What happens to the electroscope's leaves when the pipe is close? Why?

Draw the pipe as negative brought near the electroscope…draw what happens to the charge on the electroscope. BEFORE: DURING: AFTER:

b. What is the charge on the leaves while the pipe is held close to the electroscope?

c. Remove the pipe. What happens to the leaves? Why? What is the charge on the leaves now? 7. Charging by INDUCTION (permanently)

a. Charge the white pipe negatively. Bring it close to the neutral electroscope, but not touching. WITH THE PIPE STILL CLOSE TO THE ELECTROSCOPE, have your partner touch the electroscope with their finger (opposite side of where the pipe is—see picture below). Remove their finger BEFORE you remove the pipe.

b. The leaves should stay apart and the electroscope should be charged. If it is not, repeat the step above. If it doesn’t work again, get help from your charming, witty, phun physics teacher.

c. Now test the electroscope for what charge it has. Use the methods described to you in procedure #5.

What is the charge of the electroscope?

d. Complete the diagrams below by drawing in the charge on the electroscope, including its leaves, AND explain how the electroscope became charged.

EXPLANATION:

e. What is the function of your finger?

Questions:

1. When an electroscope is charged by conduction, it will have the _____same OR opposite__ charge as the rod.

2. When an electroscope’s leaves are charged temporarily by induction, the leaves will have the

______same OR opposite__ charge as the rod.

3. When an electroscope is permanently charged by induction, it will have the _____same OR opposite__ charge as the rod.

4. Thinking about the atom and where the protons, neutrons and electrons are located in an atom, explain why the “charge” referred to in this lab is always describing electrons. (Why not protons?) 5. Assume sphere A and sphere B are neutral metal conducting objects to begin with and are touching (as illustrated below). Then a positively charged rod is brought near to the sphere A (as shown in the picture below). The metal spheres are mounted on insulating bases. What is the charge on A and B below and why?

Charge on A:______Charge on B:______Why? (explain)

6. What will be the charge on A, if A and B above are separated while the charged rod is kept near them? (Refer to picture above.)

7. Explain what charging by CONDUCTION is.

8. Explain what charging by INDUCTION is.

9. There is a third method to charge objects besides conduction and induction that you used in the lab. Explain this 3rd method. (Hint: look at the very first procedure.)

10. Explain how the white pvc pipe became negatively charged with the rabbit fur. 11. Explain how the clear plastic rod became positively charged with the white cloth.