CHAPTER 7 SUMMARY
Make a Summary
(Page 376)
kq1q2
. Force is a vector and this applies to point charges (not parallel plates
r2
or other more complicated charge distributions.) This equation is used to derive many of the other equations in this chapter
such as the electric field, electric potential energy, and electric potential either directly or indirectly. For the electric field of a
kq
point charge we have ε = 21 which is a vector. It can be justified by eliminating the second charge in Coulomb’s law.
r
The electric potential energy between two point charges is related to the electric force in a similar manner as
kq q
gravitational potential energy is related to the gravitational force. The equation EE = 1 2 applies to point charges only and
r
kq1
represents a scalar. The energy per unit charge or electric potential V =
is also a scalar for point charges derived from the
r
electric potential energy. As a result we can write E = qV and for charged parallel plates we can find the electric field between
From Coulomb’s law we have the equation FE =
the plates using the equation ε =
V
.
r
CHAPTER 7 SELF QUIZ
(Page 377)
True/False
1.
2.
3.
4.
5.
6.
F The forces are the same in magnitude.
F The electric force can also repel and depends on charge not mass, etc.
T
F The electric field lines indicate the direction of the net electric force on a positive charge.
F The charge will stay on the outer surface of the car.
T
Multiple Choice
7.
(b)
8.
(e) F =
F=
9.
10.
11.
12.
13.
k (2q1 )q2
(3r ) 2
2 kq1 q2
9 r2
 32 
(e) ε 2 = ε1  2 
6 
(e)
(b)
(b)
(b)
CHAPTER 7 REVIEW
(Pages 378–379)
Understanding Concepts
1. (a) Charge transmitted to the child’s hair causes the individual strands of hair to repel each other and as a result the hair
stands on end.
(b) Charge is also transmitted to this child having the same effect on the hair.
(c) If the children were grounded the would lose the excess charge and the hair would return to normal. Therefore they are
not grounded.
462 Unit 3 Electric, Gravitational, and Magnetic Fields
Copyright © 2003 Nelson