1. No category

Electric Potential - Phys 208
1. Work & Forces & Energy
1.1 A object and some Forces
An object travels from
to
while two equal forces are applied to it. Write expressions
for, or indicate if zero, the following quantities. Be sure to also note the sign of the work (i.e.
positive or negative). Come up with an example situation that this could apply to.
a. The work done by
on the object.
b. The work done by
on the object.
c. The net work done on the object.
d. The change in kinetic energy of the object from
to
.
e. What if the two forces are not equal? Repeat the four questions for the case that
is double the
magnitude of
1.2 Charge in a uniform E field.
An electron is shot into a region of uniform electric field as shown. The opening is much smaller
than the length and width of the system.
a. Using the concepts associated with Newton's second law (i.e force and
accleration) and basic kinematics, describe the motion of the electron after it
enters the region of uniform E field.
b. Given the charge density on each plate, , the initial velocity, and the
length , find an expression that would give a number for the final velocity of
the electron when it reaches the positive plate.
c. Now explain the situation using the conservation of mechanical energy.
d. Find an expression for the work done by the electric field while the particle is inside the parallel
plates.
e. Show how this leads to the same expression you arrived above for the final velocity of the
particle when it reaches the positive plate.
2. The Electric Potential
2.1 Bring that charge closer
A positive test charge
is located very far (i.e.
) from a source charge (sphere with
charge
). It is then brought closer to the source charge, by a force
until it is
away.
a. How much work is done by the force
process?
on the test charge during this
b. How much work is done by the electric field of the source charge on the
test charge during this process?
c. If the particle starts at rest and ends at rest, what is the change in kinetic
energy?
d. If the particle starts at rest and ends at rest, what is the change in electric potential energy?
e. Knowing that the electric potential that a test charge experiences is equal to its electric potential
energy divided by its charge, what is the electric potential at point . (You can set the electric
potential at
to zero.) ?
f. Make a plot of the electric potential as a function of for this source charge.