Charging Objects

1. Charging Objects

2. Three Types of Charging • Charging by Contact • Charging by Friction • Charging by Conduction • Charging by Induction • Charging by Polarization

3. Charging by Friction The presence of different atoms in different objects results in different electrical properties such as electron affinity. One object (an insulator) is frictionally-rubbed with another object.

4. Example: Charging by Friction

5. How will we know what charge? Using the Triboelectric Series, you can predict where you are giving an object a positive or negative charge. Objects at the top gain electrons (have higher electron affinity), while those at the bottom lose electrons.

6. Charging by Friction Law of Conservation of Charge Net Charge must always remain the same in a system. Follows logically from the Law of Conservation of Matter (an electron is matter).

7. Check Point Saran Wrap has a larger electron affinity than Nylon. If Nylon is rubbed against Saran Wrap, which would end up with the excess negative charge? Explain.

8. Check Point A physics teacher rubs a glass object and a felt cloth together and the glass becomes positively charged. Which of the following statements are true? Circle all that apply. a. The glass gained protons during the rubbing process. b. The felt became charged negatively during this rubbing process. c. Charge is created during the rubbing process; it is grabbed by the more charge- hungry object. d. If the glass acquired a charge of +5 units, then the felt acquires a charge of -5 units. e. This event violates the law of conservation of charge. f. Electrons are transferred from glass to felt; protons are transferred from felt to glass. g. Once charged in this manner, the glass object and the felt cloth should attract each other. h. In general, glass materials must have a greater affinity for electrons than felt materials.

9. Charging by Conduction Involves contact between charged and uncharged objects.

10. Charging by Conduction

11. Charging by Conduction Only conductors conduct, so insulators cannot be used to charge by conduction! Insulator to Conductor interactions result in polarization.

12. Check Point A neutral metal sphere is touched by a negatively charged metal rod. As a result, the sphere will be ____ and the metal rod will be ____. Select the two answers in their respective order. • positively charged • negatively charged c. neutral d. much more massive e. ... not enough information to tell

13. Grounding Removal of electrons The earth (endless reservoir for electrons) and the human body can ground You need a conductor to ground something

14. Check Point A positively charged pop can is touched by a person standing on the ground. The pop can subsequently becomes neutral. The pop can becomes neutral during this process because ______. a. electrons pass from the pop can to the person (ground) b. electrons pass from the person (ground) to the pop can c. protons pass from the pop can to the person (ground) d. protons pass from the person (ground) to the pop can

15. Charging by Induction

16. Charging by Induction A single sphere system

17. Charging by Induction Don’t have a conducting sphere?

18. Key Point about Induction No direct contact between charge-giver and charge-taker.

19. Check Point Two neutral conducting pop cans are touching each other. A positively charged balloon is brought near one of the cans as shown below. The cans are separated while the balloon is nearby, as shown. After the balloon is removed the cans are brought back together. When touching again, can X is ____. a. positively charged b. negatively charged c. neutral d. impossible to tell

20. Independent Assignment Come up to the front when your group is called and observe the electroscope demonstration. In the meantime, work on IP Worksheet covering all “Charging” topics.