Physics 202 MWF 10:20 Spring 1999 (Ford)
Exam I Chapts. 18--20 in Cutnell and Johnson 4e
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(18 pts) 1. Point A is at a potential of +250 V. A small particle with charge q = -3.0 × 10-3 C has kinetic energy 0.50 J at point A and 0.90 J of kinetic energy at point B. The electric force is the only force on the particle. What is the potential of point B?
Ans. _______________
(22 pts) 2. Point charges q1 = -4.0 × 10-9 C and q2 = +6.0 × 10-9 C are held fixed on the x-axis as shown in the sketch. Point P is at the origin.
a) What are the magnitude and direction of the resultant electric field at point P produced by these two charges?
Ans. E = _____________
direction ____________
b) A third point charge q3 = -8.0 × 10-9 C is placed at point P. What are the magnitude and direction of the resultant force on q3 exerted by the electric field of the other two charges?
Ans. F = _____________
direction ______________
(18 pts) 3. Two spherical shells have a common center. A charge
q1 = 2 × 10-6 C is spread uniformly over the inner shell and charge q2 = - 5 × 10-6 C is spread uniformly over the outer shell. The inner shell has radius r1 = 0.10 m and the outer shell has radius r2 = 0.20 m.
Find the magnitude of the electric field at a distance from the common center of
a) 0.05 m (inside both shells)
Ans. ______________
b) 0.15 m (between the shells)
Ans. ______________
c) 0.25 m (outside both shells)
Ans.______________
(22 pts) 4. Three capacitors are connected to a battery as shown in the sketch. Sufficient time has passed for all the capacitors to be fully chrged. Capacitor C1 has charge q1 = 9.0 × 10-6 C. What is
a) the charge q2 on C2?
Ans. _____________
b) the charge q3 on C3?
Ans. _____________
c) the voltage V of the battery?
Ans. _____________
(20 pts) 5. In the circuit shown in the sketch what is the resistance R and the emf 
? Note that two currents are given.
Ans. R = ______________
= ______________