Physics 202 MWF 10:20 Spring 1994 (Ford)
Exam I Chapts. 24-27 in SZY College Physics 7e
Show all your work. Partial credit will be given if earned. Write your
answers in the blanks provided.
(18 pts) 1. A small object with charge q is released
from rest at point a where the electric potential is +12.0 V. The
particle moves because of the electric force on it and as it passes
through point b where the potential is +4.0 V its kinetic energy is
3.0 × 10-6 J. The electric force on the object is the only
force on it. What is q (sign and magnitude)?
Ans. ___________________
(20 pts) 2. Point charges q1 = -5.0 × 10-6 C
and q2 = -2.0 × 10-6 C are 0.10 m apart, as
shown in the sketch.
a) What are the magnitude
and direction of the resultant electric field at point P, which
is midway between the two charges?
Ans. magnitude __________________
direction (to the left or to the right?) __________________
b) A negative charge q3 = -4.0 × 10-6 C
is placed at point P. What are the magnitude and direction of the
force exerted on q3 by the resultant
electric field of the other two charges?
Ans. magnitude _______________
direction (to the left or to the right?) __________________
(22 pts) 3. Point charges q1 = -2.0 × 10-6 C
and q2 = +3.0 × 10-6 C are held fixed at
opposite corners of a rectangle as shown in the sketch.
a) Calculate the electric potential at point a and the electric
potential at point b due to these two charges.
Ans. Va = ___________________
Vb = ___________________
b) Calculate the work done by the electric force on a third charge when it
moves from point a to point b along a diagonal of the rectangle.
(You must indicate whether this work is positive or negative.)
The third charge has q3 = -8.0 × 10-6 C.
Ans. ______________
(16 pts) 4. Positive charge is uniformly distributed throughout
a spherical volume of radius R. The charge per unit volume is
.
(The charge is distributed in an insulator, not in a conductor.)
In terms of what is the magnitude of the electric
field
a) outside the volume a distance r from the center of the sphere
(r>R) (to get credit for this problem you must show clearly how
you obtain your answer)
Ans. ______________
b) inside the volume a distance r from the center of the sphere
(r<R) (to get credit for this problem you must show
clearly how you obtain your answer)
Ans. ____________
(24 pts) 5. In the circuit shown in the sketch
C1 = 4.0 µF,
C2 = 8.0 µF, C3 = 5.0 µF,
and C4 = 3.0 µF. The potential
difference applied across the network is 90 V.
Calculate the charge on each
capacitor and the potential difference across each capacitor.
Ans. Q1 ________________
Q2 _______________
Q3 _______________
Q4 _______________
V1 _______________
V2 _______________
V3 ________________
V4 _______________