ASSIGNMENT #8
DUE ON NOVEMBER
3, 2005
HAND-IN
CHAPTER #24:
QUESTIONS:
8 Figure 24-27
gives the electric
potential V as a function of x. (a) Rank the five
regions according to the magnitude of the x component of the electric
field within them, greatest first. What is the direction of the
field along the x axis in (b) region 2 and (c) region 4?
PROBLEMS:
•••36 The thin plastic rod of length L
= 10.0 cm in Figure 24-44
has a nonuniform linear charge
density
, where c = 49.9 pC/m. (a)
With V = 0 at infinity, find the electric
potential at point P2 on the y axis at y
= D = 3.56 cm. (b) Find the electric
field component Ey at P2.
(c) Why cannot the field component Ex at P2
be found using the result of (a)?
101 A thick-walled spherical shell
of charge
Q and uniform volume charge density
is bounded by radii r1 and r2
> r1. With V = 0 at infinity, find the electric potential
V as a function of distance r from the center of the
distribution, considering regions (a) r > r2, (b) r2
> r > r1, and (c) r < r1.
(d) Do these solutions agree with each other at r = r2
and r = r1? (Hint: See Section 23-9.)
CHAPTER #25:
QUESTIONS:
PROBLEMS:
50 The chocolate crumb mystery.
This story begins with Problem 54 in
Chapter 23.
As part of the investigation of the biscuit factory explosion, the electric
potentials of the workers were measured as they emptied sacks of chocolate
crumb powder into the loading bin, stirring up a cloud of the powder around themselves. Each worker had an electric potential
of about 7.0 kV relative to the ground, which was taken as zero potential.
(a) Assuming that each worker was effectively a capacitor
with a typical capacitance
of 200 pF, find the energy stored in that effective
capacitor. If a single spark between the worker and any conducting object
connected to the ground neutralized the worker, that energy would be
transferred to the spark. According to measurements, a spark that could ignite
a cloud of chocolate crumb powder, and thus set off an explosion, had to have an energy of at least 150 mJ. (b)
Could a spark from a worker have set off an explosion in the cloud of powder in
the loading bin? (The story continues with Problem 48 in
Chapter 26.)
59 In Figure 25-49, V
= 20 V, C1 = 2.0 
, C2 = 16 , and C3 = C4 = 8.0 . Switch S is first thrown to the left until capacitor
1 reaches equilibrium. Then the switch is thrown to the right. When equilibrium
is again reached, (a) how much charge is on C2 and (b) what is the potential
across C2?
CHAPTER #26:
QUESTIONS:
PROBLEMS:
48 The chocolate crumb mystery.
This story begins with Problem 54 in
Chapter 23
and continues through Chapter 24 and
Chapter 25.
The chocolate crumb powder moved to the silo through a pipe of radius R
with uniform speed v and uniform charge
density
. (a) Find an expression for the current
I (the rate at which charge on the powder moved) through a perpendicular
cross section of the pipe. (b) Evaluate I for
the conditions at the factory: pipe radius R = 5.0 cm, speed v =
2.0 m/s, and charge density 
If the powder were to flow through a change V
in electric potential,
its energy could be transferred to a spark at the rate P = IV.
(c) Could there be such a transfer within the pipe due to the radial potential
difference discussed in Problem 60 of
Chapter 24?
As the powder flowed from the pipe into the
silo, the electric
potential of the powder changed. The magnitude of that change
was at least equal to the radial potential
difference within the pipe (as evaluated in Problem 60 of
Chapter 24).
(d) Assuming that value for the potential
difference and using the current
found in (b) above, find the rate at which energy could have been transferred
from the powder to a spark as the powder exited the pipe. (e) If a spark did
occur at the exit and lasted for 0.20 s (a reasonable expectation), how much
energy would have been transferred to the spark?
Recall from Problem 54 in
Chapter 23
that a minimum energy transfer of 150 mJ is needed to
cause an explosion. (f) Where did the powder explosion most likely occur: in
the powder cloud at the unloading bin (Problem 50 of
Chapter 25),
within the pipe, or at the exit of the pipe into the silo?
ONLINE
CHAPTER #25:
QUESTIONS:
PROBLEMS:
••11 In Figure 25-28, a
potential
difference of V = 100.0 V is applied across a capacitor
arrangement with capacitances C1 = 10.0 , C2 = 5.00 , and C3 = 4.00 . If capacitor 3 undergoes
electrical breakdown so that it becomes equivalent to conducting wire, what is
the increase in (a) the charge
on capacitor 1 and (b) the potential
difference across capacitor 1?
••12 In Figure 25-30,
the battery has a potential difference of V = 10.0 V and the five
capacitors each have a capacitance of 10.0 . What is the charge on (a) capacitor
1 and (b) capacitor 2?
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