Download Final Exam - Study Guide - Electric Fields and Electric Potential

Electric Fields and Electric Potential
Study Guide for Chapters 23 and 25
It is likely that there will be a question on the final exam involving both electric fields and electric
potential.
Chapter 23: The Electric Field
t on a charge ; is given by the equation:
An electric field exerts force on any charge. The force F
t œ ;E
t
F
t is the electric field vector at the location of the charge. Electric field is measured in
where E
newtons per coulomb (NÎC), or equivalently volts per meter (VÎm).
Coulomb's Law describes the electric field produced by a single charge:
t œ
E
" ;
rs
%1%! <#
Here < is the distance to the charge, and rs is a unit vector pointing away from the charge. When
t vectors must be added together.
multiple charges are present, the resulting E
Problems: 5a, 7, 16
t œ "#Þ* sj kVÎm
Answers: 16. (a) E
t œ $)Þ' sj mN
(b) F
Chapter 25: Electric Potential
Electric forces can also be described using electric potential. In the same way that the electric
field determines the force on a charge, the electric potential determines the potential energy.
Specifically, the potential energy Y of a charge ; is given by the equation
Y œ ;Z
where Z is electric potential. Electric potential is measure in volts, where " V œ " JÎC.
The electric field always points straight in the direction of decreasing potential, like this:
t is determined by the distance between the potential lines. For example, the
The magnitude of E
electric field in the picture above has a magnitude of & VÎcm (assuming a " cm distance between
the potential lines). In general:
t¸ œ
¸E
?Z
?=
t.
where ?= represents a distance in the direction of E
There is an electric potential version of Coulomb's law:
Z œ
" ;
%1%! <
This describes the potential due to a single point charge. When multiple charges are present, the
resulting potentials must be added together.
Problems: 3, 5, 11, 15