Reading:

Cutnell and Johnson, Chapter 18.

Problems for Review:

Reviewing these problems gives you good exposure to this week's main topics, in practice. All are worked in the Student Study Guide [SSG] or Student Solutions Manual [SSM]; solutions are posted on our website http://www.physics.emory.edu/Classes/142-003.html , for those without these texts.

Conceptual:

MCAT review problem, [SSG] p 351.

Quantitative:

Chapter 18, problems 5, 9, 13, 37, 41, 49, 65, 69.

Problems to Hand In:

Conceptual:

Use the following to answer questions 1--8:

1. Which combination of charges would yield the greatest repulsive force between the charges?
   1. -2q and -4q
   2. +1q and -3q
   3. -1q and -4q
   4. -2q and +4q
   5. +1q and +7q
2. Which combination of charges will yield zero electric field at the point x?
   1. +1q and -1q
   2. +2q and -3q
   3. +1q and -4q
   4. +1q and +4q
   5. +4q and +4q
3. Say B is uncharged and A has negative charge. An uncharged conducting sphere is brought near A (without actually touching). Which of the following describes the interaction between the sphere and A?
   1. Nothing happens, since the sphere is electrically neutral.
   2. The sphere develops negative net charge, so the sphere and charge A repel each other.
   3. The sphere develops positive net charge, so the sphere and charge A attract each other.
   4. The sphere's near side to A develops a negative charge, and its far side the opposite positive charge, so that the sphere and charge A repel each other.
   5. The sphere's near side to A develops a positive charge, and its far side the opposite negative charge, so that the sphere and charge A attract each other.

   
   

   For questions 4 and 5, take A to have charge and B to have charge , with separation distance L=0.30 m.

   
   

4. What is the magnitude and direction of the electrostatic (Coulomb) force on charge B?
   1. 2.4 N, to the right
   2. 2.4 N, to the left
   3. 4.8 N, to the right
   4. 4.8 N, to the left
   5. 7.2 N, to the right

5. Which of the following is an accurate depiction of the electric field lines due to charges A and B?

   

   
   

   For questions 6 -- 8, charges A and B are equal and positive, with a value +q. A third charge C is added, so that A, B, and C form an equilateral triangle. C has charge -q, opposite that of A and B.

   
   

6. Which of the arrows labeled a, b, c, d shown gives the correct direction of the net force acting on C?

   

7. Which of the arrows labeled a, b, c, d shown gives the correct direction of the net force acting on B?

   

8. Consider a test charge Q placed at point x. Is it possible to choose a nonzero value of Q such that the force on Q is zero?
   1. Yes, because the forces on Q are vectors and three vectors can add to zero.
   2. No, because the forces on Q are vectors and three vectors can never add to zero.
   3. Yes, because the electric force at the midpoint between A and B is zero whether a charge is placed there or not.
   4. No, because the forces on Q due to the charges at A and B point in the same direction.
   5. No, because a fourth charge would be needed to cancel the force on Q due to the charge at C.

Quantitative:

Chapter 18, problems 4, 16, 28, 32, 38, 54, 62, 64.

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