Electric Potential
Electric Potential Energy versus Electric Potential
Gravitational Force and Potential Energy
First we review the force and potential energy of an object of mass
in a uniform
gravitational field that points downward (in the
direction), like the gravitational field
near the earth's surface.
Part A
Find the force
on an object of mass
in the uniform gravitational field when it is at
height
.
Express
in terms of
,
,
, and
.
=m*g*z_unitCorrect
Because we are in a uniform field, the force does not depend on the object's location.
Therefore, the variable
does not appeaer in the correct answer.
Part B
Now find the gravitational potential energy
of the object when it is at an arbitrary
height
. Take zero potential to be at position
.
Express
in terms of
,
, and
. Note that because potential energy is a scalar, and
not a vector, there will be no unit vector in the answer.
=m*g*zCorrect
Part C
In what direction does the object accelerate when released with initial velocity upward?
downward
Correct
Electric Force and Potential Energy
Now consider the analogous case of a particle with charge
placed in a uniform electric
field of strength
, pointing downward (in the
direction)
Part D
Find
, the electric force on the charged particle at height
.
Express
in terms of
,
,
, and
.
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View Full Document=q*E*z_unitCorrect
Part E
Now find the potential energy
of this charged particle when it is at height
. Take
zero potential to be at position
.
Express
(a scalar quantity) in terms of
,
, and
.
=q*E*zCorrect
Part F
In what direction does the charged particle accelerate when released with upward initial
velocity?
upward or downward depending on its charge
Correct
Electric Field and Electric Potential
The electric potential
is defined by the relationship
, where
is the electric
potential energy of a particle with charge
.
Part G
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 Spring '09
 All
 Electric Potential, Potential Energy, Electric charge, Fundamental physics concepts, uniform electric field

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