In case A below (on the next page), a point charge +q is a distances from...

 

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In case A below (on the next page), a point charge +q is a distances from the center of a small ball with charge +Q. In case B the +q charge is a distance s from the center of an acrylic rod with a total charge +Q. Consider the following dialogue between two students, neither of whom are completely correct: - - Student 1: "The charged rod and the charged ball have the same charge, +Q, and are the same distance from the point charge, +q. So the force on +q will be the same in both cases." Student 2: "No, in case B there are charges spread all over the rod. The charge directly below the point charge will exert the same force on +q as the ball in case A. The rest of the charge on the rod will make the force in case B bigger." 1. Discuss with your group the errors made by each student. 2. Write a correct description of how the forces compare. 3. Suppose you were given the values of q, Q, and s. Discuss possible methods you might use to calculate the electric force on +q. (You do not have to calculate this force.) Case A +q Case B +q 0 Uniformly charged rod with total S S charge +Q +Q In case A below (on the next page), a point charge +q is a distances from the center of a small ball with charge +Q. In case B the +q charge is a distance s from the center of an acrylic rod with a total charge +Q. Consider the following dialogue between two students, neither of whom are completely correct: - - Student 1: "The charged rod and the charged ball have the same charge, +Q, and are the same distance from the point charge, +q. So the force on +q will be the same in both cases." Student 2: "No, in case B there are charges spread all over the rod. The charge directly below the point charge will exert the same force on +q as the ball in case A. The rest of the charge on the rod will make the force in case B bigger." 1. Discuss with your group the errors made by each student. 2. Write a correct description of how the forces compare. 3. Suppose you were given the values of q, Q, and s. Discuss possible methods you might use to calculate the electric force on +q. (You do not have to calculate this force.) Case A +q Case B +q 0 Uniformly charged rod with total S S charge +Q +Q