STATIC ELECTRICITY Objects can acquire static electric charges by either gaining or losing electrons. A body that gains electrons has a net negative charge. A body that loses electrons has a net positive charge. Any object can acquire a static electric charge (a charge at rest). However, only those objects that are separated from ground by nonconductors will retain their charge for any length of time. Bear in mind gold- or silver-leaf three rules: Equipment . electroscope cat's fur or wool pad silk pad glass rod rubber rod or vinyl strip pith ball suspended by silk thread from holder 1. Electrons are highly mobilethey can be easily moved around within a body or can be moved from one body to another. 2. Rubber rods (and many plastic strips or rods) when rubbed with wool or fur acquire electrons from the fur and thus become charged negatively. 3. Glass rods when rubbed with silk lose electrons to the silk and thus become charged positively. If a negative charge is brought close to a suspended, uncharged Noaltiveiy-charged rod Negatively-charged rod pith ball (Figure 3771), electrons on the side of the pith ball facing the charge will be repelled to the other side of the ball. The side of the pith ball facing the negative charge will become Nmvglygh.fm positive, and the ball will be attracted to the negative charge. (Unlike charges attract one another.) As the bodies touch, electron will move from the negative body onto the positive side of the pith ball. The pith ball now has an excess of electrons. Thus, the pith M ball has acquired a net negative charge. It is then repelled by the new 314. w OW m \"mm\" on m. m\" pun \"I \"m, u i, mum negatively charged body. (Like charges repel one another.) to the ma. {bl Aim In: ball acquire. a charge. a ll topollod Obiective During this investigation you will use pith balls and an electroscope to investigate some behaviors of static charges. Procedure Record your observations in the spaces provided in the Data and Observations section of this investigation. A. Charging a Pith Ball 1. Rub the rubber rod with fur or wool. Then bring the rod close to a suspended pith ball. L\Data and Observations A. Charging a Pith Ball Describe the behavior of the pith ball. B. Charging the Electroscope by Conduction Summarize your observations involving charging the electroscope by conduction. C. Testing the Charge on an Object 1. Describe your observations in Step 2. (This is how the leaves of an electroscope behave when the electroscope is approached by an opposite charge.) 2. Describe your observations in Step 3. (This is how the leaves of an electroscope behave when the electroscope is brought near to a like charge.) D. Charging the Electroscope by Induction 1. Summarize your observations om Steps 1 and 2. 2. Summarize your observations from Steps 3 and 4. 3. Record your observations from Steps 5 and 6. Interpretation 1. What is the charge on a rubber rod rubbed with fur? 2. What is the charge on a glass rod rubbed with silk? 3. The action between the rubber rod and the pith ball was explained in the rst part of the procedure. The action between the glass rod and the pith ball was not explained. The actions are similar but are not exactly the same. Using the theory that only electrons move, write a paragraph explaining what you think caused the pith ball to behave the way it did when the glass rod was brought close to it. 4. Like charges while unlike charges 5. a. In Procedure B, why did the leaves of the electroscope diverge when the negatively-charged rod touched it? b. Explain why the leaves remained apart when the charged rod was removed. 6. Explain the difference in the behavior of the electroscope in Observations D1 and D-Z. 7. Explain why the electroscope acquired a positive charge in Procedure D. 8. Explain the function of your nger in Procedures B and D. 9. Compared with the charging body, what is the charge on an electroscope when it is charged by (a)conduction? (b)induction? 10. Study Figure 37-3. State what charges you think will exist on Ball A and on Ball B if the two balls are rst separated and then the charged rod is removed. Explain. thuro 37-3