This preview shows pages 1–3. Sign up to view the full content.
CHAPTER
24
Electric Potential
1*
·
A uniform electric field of 2 kN/C is in the
x
direction. A positive point charge
Q
= 3
μ
C is released from rest at
the origin. (
a
) What is the potential difference
V
(4 m) –
V
(0)? (
b
) What is the change in the potential energy of the
charge from
x
= 0 to
x
= 4 m? (
c
) What is the kinetic energy of the charge when it is at
x
= 4 m? (
d
) Find the
potential
V
(
x
) if
V
(
x
) is chosen to be (
d
) zero at
x
= 0, (
e
) 4 kV at
x
= 0, and (
f
) zero at
x
= 1 m.
(
a
) Use Equ. 242
b
; ?
V
= –
E
?x
(
b
) ?
U
=
q
?
V
(
c
) Use energy conservation
(
d
), (
e
), (
f
) Use Equ. 242
b
?
V
= –8 kV
?
U
= –24 mJ
K
= 24 mJ
(
d
)
V
(
x
) = –(2 kV/m)
x
; (
e
)
V
(
x
) = 4 kV – (2 kV/m)
x
;
(
f
)
V
(
x
) = 2 kV –(2 kV/m)
x
2
·
An infinite plane of surface charge density
s
= +2.5
μ
C/m
2
is in the
yz
plane. (
a
) What is the magnitude of the
electric field in newtons per coulomb? In volts per meter? What is the direction of
E
for positive values of
x
? (
b
)
What is the potential difference
V
b
–
V
a
when point
b
is at
x
= 20 cm and point
a
is at
x
= 50 cm? (
c
) How much
work is required by an outside agent to move a test charge
q
0
= +1.5 nC from point
a
to point
b
?
(
a
)
E
x
=
s
/2
e
0
(
b
) ?
V
= –
E
x
?
x
(
c
)
W
= ?
U
=
q
?
V
E
x
= (2.5
×
10
–6
/2
×
8.85
×
10
–12
) N/C = 141 kN/C
V
b
–
V
a
= (–141
×
–0.3) kV = 42.4 kV
W
= (42.4
×
10
3
×
1.5
×
10
–9
) J = 63.6
μ
J
3
·
Two large parallel conducting plates separated by 10 cm carry equal and opposite surface charge densities such
that the electric field between them is uniform. The difference in potential between the plates is 500 V. An electron
is released from rest at the negative plate. (
a
) What is the magnitude of the electric field between the plates? Is the
positive or negative plate at the higher potential? (
b
) Find the work done by the electric field on the electron as the
electron moves from the negative plate to the positive plate. Express your answer in both electron volts and joules.
(
c
) What is the change in potential energy of the electron when it moves from the negative plate to the positive plate?
What is its kinetic energy when it reaches the positive plate?
(
a
)
E
is uniform;
E
= ?
V
/?
x
(b) W
=
q
?
V
(c) ?
U
= –
W
;
K
=
W
E
= 500/0.1 V/m = 5 kV/m; high
V
at the positive plate
W
= 500
×
1.6
×
10
–19
J = 8
×
10
–17
J = 500 eV
?
U
= –500 eV;
K
= 500 eV
This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentChapter 24
Electric Potential
4
·
Explain the distinction between electric potential and electrostatic potential energy.
The difference is analogous to that between gravitational potential and gravitational potential energy. Electrostatic
potential refers to the difference in potential energy per unit charge between the point of interest and an arbitrary
reference point; electrostatic potential energy is the potential energy of a charge with respect to an arbitrary zero.
5* ·
This is the end of the preview. Sign up
to
access the rest of the document.
 Spring '08
 Halliday

Click to edit the document details