Part I: A. Charge and Coulomb's Law


x =  m        q = C

Please wait for the animation to completely load.

This animation allows you to add charges, move them around and see the force vectors between the charges. Use the text box for charge to add the charges.  The arrows on the screen show how the particles interact with each other by showing both the magnitude (relative size of the arrow) and direction of the electrostatic force.   Restart.

  1. Use the animation to create three like charges at x = -1 m, x = 0 m, and x = 1 m.  You can do this by entering the position in the text box and clicking the add button (position is given in meters).  Sketch a diagram.
  2. What is the net force on the middle charge? 
  3. Now move one of the outer charges around.  Sketch your diagram.
  4. Is the force on the middle charge still zero?  Explain.
  5. Push "reset" to clear the charges and set up two identical positive charges 1-m apart.  Sketch your picture.
  6. Move one charge toward the other and away from the other.  What happens to the force between the two charges as you change the distance between the charges?

The force between two particles always lies on the line between the two particles, is attractive or repulsive depending on the signs of the charges, and varies as 1 over the square of the separation distance (1/r2) (from Coulomb's Law).

  1. Add a few charged particles with the same magnitude of charge (and with both positive and negative sign), and move them around by click-dragging them.  Sketch a diagram of one of your configurations (with the force vectors).
  2. Now reset the animation and create two charges with different amounts of charge but of the same polarity (same sign: either both positive or both negative).  Sketch a diagram and include the force vectors.
  3. Describe the similarities and differences in the force vectors on each particle.
  4. Reset the animation and create two charges of different magnitude and opposite polarity.  Sketch a diagram including the force vectors.
  5. Describe the similarities and differences in the force vectors on each particle.



Original problem: Illustration 22.1 Physlet Physics by Christian and Belloni
2004 by Prentice-Hall, Inc. A Pearson Company