PHYS 2064
Chapter 15 Problems

Objectives

  1. Differentiate between positive and negative charge.  Define Coulomb's Law.  Be able to calculate the force on a charge due to other charges.
  2. Differentiate between conductors and insulators.  Describe how to transfer charges to each via contact or induction.
  3. Define electric field.  Be able to calculate the electric field due to various charge configurations.
  4. Define Gauss' Law.  Be able to use this law to make qualitative arguments about the amount of charge contained by a surface.

Conceptual Questions

  1. After rubbing an inflated balloon vigorously through one's hair (assuming that one is not folically challenged), the balloon can be suspended from a wooden surface (eg. a wooden door). How is this done?
  2. How would physics be different if the electron had a positive charge, and the proton had a negative charge?
  3. When you shuffle your rubber-soled feet across a carpet, you pick up a net charge. What kind of atmospheric conditions enhance this situation?
  4. You are caught outside during a storm. What are some good methods to use to avoid being struck by lightning?
  5. How does a Van de Graf generator work?

Questions

  1. Suppose that 1.00 gm of hydrogen is separated into electrons and protons. Suppose also that the protons are placed at the Earth's North Pole, and the electrons are placed at the South Pole. What is the resulting force on the Earth?
  2. Three charges are arranged as shown in Figure 15.12 (a 3 nC charge on the y-axis at y=0.5 m, a 2 nC charge on the y-axis at y = -0.5 m, and a 6 nC charge on the x-axis at x=0.5 m). Find the magnitude and direction of the electrostatic force on the 6.00 nC charge.
  3. An electron and a proton both start from rest and from the same point in a uniform electric field of 370 N/C. How far apart are they 1.0 x 10-6 s after they are released? Ignore the attraction between the electron and the proton.
  4. A piece of aluminum foil of mass 5.00 x 10-2 kg is suspended by a string in an electric field directed vertically upward. If the charge on the foil is 3.00 x 10-6 C, find the strength of the field that will reduce the tension in the string to zero.
  5. A proton accelerates from rest in a uniform electric field of 640 N/C. At some later time, its speed is 1.20 x 106 m/s. (a) Find the magnitude of the acceleration of the proton. (b) How long does it take the proton to reach this speed? (c) How far has it moved in this interval? (d) What is its kinetic energy at the later time?
  6. A small 2.00 gm plastic ball is suspended by a 20.0 cm long string in a uniform electric field, as shown in Figure 15.50. If the ball is in equilibrium when the string makes a 15.0o angle with the vertical as indicated, what is the net charge on the ball?

Solutions

If you find an error in these, or just have a comment, send an e-mail message to jpratte@astate.edu