Physics 202 MWF 12:40 Spring 1993 (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.
(14 pts) 1. A particle with charge q = -2.0 × 10-6 C is
released
from rest at point a where the electric potential is -30.0 V. The
particle moves because of the electric force on it and as it passes
through point b that is 0.40 m from point a its kinetic energy is
3.0 × 10-5 J. What is the electric potential at point b?
(You must say whether the potential is positive or negative.)
Ans. ___-15 V___
(24 pts) 2. Point charge q1 = +2.0 × 10-9 C
is placed on the
x-axis at x = -0.5 m and point charge
q2 = +4.0 × 10-9 C is placed
on the x-axis at x = +2.0 m.
a) Calculate the magnitude and direction of the resultant electric field at
the origin produced by these two charges.
Ans. E = ___63 N/C___
direction = ___+x-direction___
b) Calculate the electric potential at the origin produced by these two
point charges. You must indicate whether the potential is positive or
negative. (Take V = 0 at r goes to infinity for a point charge.)
Ans. ___54 V___
(24 pts) 3. A small conducting spherical shell with inner radius a
and outer
radius b is concentric with a larger conducting spherical shell with
inner radius c and outer radius d. The inner shell has
total charge +2q and the outer shell has total charge +4q.
a) Calculate the electric field in terms of q and the distance
r from the common center of the two shells for
i) b<r<c (between the two shells)
Ans. ___E = 2q/4
0r2___
ii) r>d (outside the large shell)
Ans. ___E = 6q/4
0r2___
b) What is the total charge on the
i) outer surface of the small shell
Ans. ___+2q___
ii) outer surface of the large shell
Ans. ___+6q___
(14 pts) 4. A parallel-plate capacitor has capacitance
C = 5.0 × 10-12 F.
The separation between the plates is d = 2.0 × 10-3 m.
What is the maximum magnitude of charge Q that can be placed on
each plate if the electric
field in the region between the plates is not to exceed
3.0 × 104 V/m?
Ans. ___3.0 × 10-10 C___
(24 pts) 5. Three capacitors are connected to a potential difference of 120 V,
as shown in the sketch. The capacitors have capacitances
C1 = 6.0 × 10-6 F,
C2 = 3.0 × 10-6 F,
C3 = 5.0 × 10-6 F.
Calculate the magnitude of the charge Q on each capacitor and the
potential V across each capacitor.
Ans. Q1 = ___2.4 × 10-4 C___
V1 = ___40 V___
Q2 = ___2.4 × 10-4 C___
V2 = ___80 V___
Q3 = ___6.0 × 10-4 C___
V3 = ___120 V___