Conceptual Questions

  1. Can an insulator be charged? If so, how would you charge an insulator? If not, why not?

  2. Can a conductor be charged? If so, how would you charge a conductor? If not, why not?

  3. Four lightweight balls A, B, C, and D are suspended by threads. Ball A has been touched by a plastic rod that was rubbed with wool. When the balls are brought close together, without touching, the following observations are made:

    • Balls B, C, and D are attracted to ball A.

    • Balls B and D have no effect on each other.

    • Ball B is attracted to ball C.

    What are the charge states (glass, plastic, or neutral) of balls A, B, C, and D? Explain.

  4. Charged plastic and glass rods hang by threads.

    1. An object repels the plastic rod. Can you predict what it will do to the glass rod? If so, what? If not, why not?

    2. A different object attracts the plastic rod. Can you predict what it will do to the glass rod? If so, what? If not, why not?

  5. A lightweight metal ball hangs by a thread. When a charged rod is held near, the ball moves toward the rod, touches the rod, then quickly “flies away” from the rod. Explain this behavior.

  6. A plastic balloon that has been rubbed with wool will stick to a wall. Can you conclude that the wall is charged? If so, where does the charge come from? If not, why does the balloon stick?

  7. Suppose there exists a third type of charge in addition to the two types we’ve called glass and plastic. Call this third type X charge. What experiment or series of experiments would you use to test whether an object has X charge? State clearly how each possible outcome of the experiments is to be interpreted.

  8. The two oppositely charged metal spheres in FIGURE Q22.8 have equal quantities of charge. They are brought into contact with a neutral metal rod. What is the final charge state of each sphere and of the rod? Use both charge diagrams and words to explain.

    FIGURE Q22.8

    The figure illustrates two oppositely charged metal spheres brought in contact with a neutral metal rod.

  9. Metal sphere A in FIGURE Q22.9 has 4 units of negative charge and an identical metal sphere B has 2 units of positive charge. The two spheres are brought into contact. What is the final charge state of each sphere? Explain.

    FIGURE Q22.9

    The figure illustrates two identical metal spheres with unequal charges brought in contact with each other.

  10. A negatively charged electroscope has separated leaves.

    1. Suppose you bring a negatively charged rod close to the top of the electroscope, but not touching. How will the leaves respond? Use both charge diagrams and words to explain.

    2. How will the leaves respond if you bring a positively charged rod close to the top of the electroscope, but not touching? Use both charge diagrams and words to explain.

  11. Metal spheres A and B in FIGURE Q22.11 are initially neutral and are touching. A positively charged rod is brought near A, but not touching. Is A now positive, negative, or neutral? Use both charge diagrams and words to explain.

    FIGURE Q22.11

    The figure illustrates a positively charged rod brought near two neutral spheres touching each other.

  12. If you bring your finger near a lightweight, negatively charged hanging ball, the ball swings over toward your finger as shown in FIGURE Q22.12. Use charge diagrams and words to explain this observation.

    FIGURE Q22.12

    The figure illustrates a negatively charged ball hanging by a string connected to a horizontal surface at the top attracted toward a neutral finger.

  13. Reproduce FIGURE Q22.13 on your paper. Then draw a dot (or dots) on the figure to show the position (or positions) where an electron would experience no net force.

    FIGURE Q22.13

    The figure illustrates two charged particles placed at a distance from each other.

  14. Charges A and B in FIGURE Q22.14 are equal. Each charge exerts a force on the other of magnitude F. Suppose the charge of B is increased by a factor of 4, but everything else is unchanged. In terms of F, (a) what is the magnitude of the force on A, and (b) what is the magnitude of the force on B?

    FIGURE Q22.14

    The figure consists of two parts that illustrate the force exerted by two charged particles on each other.

  15. The electric force on a charged particle in an electric field is F. What will be the force if the particle’s charge is tripled and the electric field strength is halved?