Physics 181, Questions & Answers

Physics 181, Questions & Answers 1. Which one of the following statements best explains why tiny bits of paper are attracted to a charged rubber rod? - C) The paper becomes electrically polarized by induction. 2. Five styrofoam balls are suspended from insulating threads. Several experiments are performed on the balls; and the following observations are made: I. Ball A attracts B and A repels C. II. Ball D attracts B and D has no effect on E. III. A negatively charged rod attracts both A and E. What are the charges, if any, on each ball? - C) + - + 0 0 3. Two uncharged conducting spheres, A and B, are suspended from insulating threads so that they touch each other. While a negatively charged rod is held near, but not touching sphere A, someone moves ball B away from A. How will the spheres be charged, if at all? - E) Sphere A: + Sphere B: - 4. Each of three objects has a net charge. Objects A and B attract one another. Objects B and C also attract one another, but objects A and C repel one another. Which one of the following table entries is a possible combination of the signs of the net charges on these three objects? - D)- + - 5. A conducting sphere has a net charge of -6.4 × 10-17 C. What is the approximate number of excess electrons on the sphere? - D) 400 6. Complete the following statement: When an ebonite rod is rubbed with animal fur, the rod becomes negatively charged as - D) negative charges are transferred from the fur to the rod. 7. Complete the following statement: When a glass rod is rubbed with silk cloth, the rod becomes positively charged as - B) negative charges are transferred from the rod to the silk. 8. A charged conductor is brought near an uncharged insulator. Which one of the following statements is true? - B) Both objects will attract each other. 9. An aluminum nail has an excess charge of +3.2 µC. How many electrons must be added to the nail to make it electrically neutral? - A) 2.0 × 10^13 10. Two uncharged, conducting spheres, A and B, are held at rest on insulating stands and are in contact. A positively charged rod is brought near sphere A as suggested in the figure. While the rod is in place, someone moves sphere B away from A. How will the spheres be charged, if at all? - C) Sphere A: negative Sphere B: positive 11. Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of -2.0 µC; sphere B carries a charge of -6.0 µC; and sphere C carries a charge of +4.0 µC. Spheres A and B are touched together and then separated. Spheres B and C are then touched and separated. Does sphere C end up with an excess or a deficiency of electrons and how many electrons is it? - E) There is no excess or deficiency of electrons. 12. Two charged particles A and B are located near one another. Both the magnitude and direction of the force that particle A exerts on particle B is independent of - E)