# Unit 8 Extra Credit

Either print this page and complete or (better yet) neatly show your answers on a separate page of paper. All answers must be expressed as complete sentences and/or all work shown to receive credit.

1. Distinguish between a positively and negatively charged object in terms of the number of protons and electrons present in the object.

2. When combing your hair, electrons are scuffed from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?

3. What is the fundamental force that underlies all "chemical" forces?

4. Explain how electrically neutral atoms and molecules are able to electrically attract each other.

5. How are electrical forces (as described by Coulomb's law) similar to gravitational forces (as described by Newton's law of gravitation)? How are they different?

6. Distinguish between a conductor and an insulator; between a conductor and a semiconductor.

7. EIn the "good ole days" (when Mr. Schmidgall was a youngster) at automobile toll-collecting stations, a thin metal wire would stick up from the road and make contact with cars before they reached the toll collector. What was the purpose of this wire?

8. Why are the tires for trucks carrying gasoline and other flammable fluids manufactured to conduct electricity?

9. If you rub an inflated balloon against your hair and place it against a door, it will stick. Explain why.

10. Explain how an electrically neutral object can be attracted to a charged object.

11. A spark will jump between you and another person if the electric field exceeds 4.0 x 106 V/m. You shuffle across a rug and a spark jumps when you stick out your finger 0.15 cm from another person's arm. Calculate the potential difference between your body and the other person's arm. PSYW

12. An oil drop carries a charge of three electrons and is suspended in an electric field of intensity 5.0 x 104 N/C. If the charge on the electron is 1.6 x 10-19 C, what is the weight of the oil drop? PSYW

13. An electric force of 2.5 x 10-4 N acts between two small equally charged spheres which are 2.0 cm apart. Calculate the force acting between the spheres if the charge on one sphere doubles and the spheres move to a 5.0 cm separation.

14. A charge of 4.0 x 10-5 C is attracted to a second charge with a 350 N force when the separation is 10.0 cm. Calculate the magnitude of the second charge. PSYW

Resources for physics students are available through links on the GBS Physics Home Page. Such resources include the Multimedia Physics Studios (a collection of animations and movies which illustrate key physics concepts) and The Physics Classroom (an online tutorial written in an easy-to-understand language).