Physics 202 MWF 10:20 Spring 1997 (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 and mass m = 0.050 kg
is placed in a
uniform electric field that is directed downward and that has magnitude
E = 8.0 × 104 N/C. What is the sign and
magnitude
of q so that the particle will remain stationary if released
from rest?
Ans. sign ____________________
magnitude _________________
(20 pts) 2. Point charge
q1 = +5.0 × 10-6 C is on
the +y-axis at
y = +0.1 m and point charge
q2 = -5.0 × 10-6 C is on
the -y-axis at
y = -0.1 m. Point P is on the +x-axis at
x = +0.2 m.
a) What are the x and y components of the resultant
electric field
produced at point P by the two point charges q1
and q2?
Ans. Ex = _________________
Ey = _________________
b) A point charge
q3 = -3.0 × 10-6 C is placed at P.
What are
the magnitude and direction of the resultant force exerted on
q3 by
the two charges q1 and q2?
Ans. F = _______________
direction ______________
(16 pts) 3. A small solid conducting sphere with radius a
is concentric
with a larger conducting spherical shell with inner radius
b and outer
radius c. The electric field for a < r < b
(in the air space between the
sphere and the shell) has magnitude
E = 3q/
4
0r
2
and is directed
in toward the center of the sphere. The electric field for
r > c (outside the
spherical shell) has magnitude
E = 4q/
40r
2
and is directed
radially outward. The parameter q represents a positive quantity
of charge.
a) What is the electric field in the region b < r < c
(inside the metal of the shell)?
Ans. ______________
b) In terms of q, what is the net charge on the solid sphere? Is the
net charge positive or negative? (To receive credit you must give the
reasoning behind your answer.)
Ans. ______________
c) In terms of q, what is the net charge on the spherical shell?
Is the
net charge positive or negative? (To receive credit you must give the
reasoning behind your answer.)
Ans. _________________
(16 pts) 4. A parallel-plate capacitor has charge
Q = 9.0 × 10-6 C
and capacitance C0 = 3.0 × 10-10 F
when there is air between the plates. Each plate has
an area of 0.14 m2.
With the charge on the plates of
the capacitor kept constant, a dielectric with K = 5 is
inserted between the
plates, completely filling the volume between the plates. After the
dielectric has been inserted,
a) what is the potential difference between the plates of the capacitor?
Ans. ________________
b) what is the magnitude of the electric field at a point midway between
the plates?
Ans. ________________
(16 pts) 5. In the circuit shown in the sketch
C2 = 3.0 µF. The potential difference
Vab
applied to the capacitor network is 120 V. The charge on the capacitor
C2 is Q2 = 1.5 × 10-4 C.
Calculate the voltage V1 for the
capacitor C1 and the voltage V3 for
the capacitor C3.
V1 _______________
V3 _______________
(18 pts) 6. A small, charged metal sphere, carrying a net charge of
q1 = +6.00 × 10-6 C, is held
in a stationary position by insulating
supports. A second small metal sphere, with a net charge of
q2 = +3.00 × 10-6 C
and a mass of 5.00 g, is projected
toward q1.
When the two spheres are 0.800 m apart, q2 is moving
toward q1 with
a speed of 12.0 m/s. Assume that the two spheres can be treated as
point charges and neglect the effects of gravity.
How close does q2 get to q1?
Ans. _______________