Energy and Potential in Uniform Fields - Modeling Physics

Electric Potential Model Worksheet 2:
Energy and Potential in Uniform Fields
1. Rank the change in gravitational potential energy for the following lettered objects in the Earth’s
gravitational field.
5 m –
4 m –
3 m –
2 m –
1 m –
ground level –
A B C D E F G
5 kg
3 kg
2 kg
Earth
6 kg
a. most _______ _________ ________ ________ _______ _______ ________
b. Explain your ranking, stating why each is greater than, less than, or equal to its neighbors.
5 kg
2 kg
5 kg
c. Where is the energy stored What gains or loses energy as the masses move from one
place to another
2. Rank the change in electrical potential energy for the following lettered objects in a uniform
electric field between two charged walls. (Ignore gravitational effects.)
a. most _____ ______ _____ ______ _____ _____
b. Explain your ranking, stating why each is greater than,
less than, or equal to its neighbors.
c. Where is the energy stored What gains or loses
energy as the charges move from one place to another
+ 1 2 3 4 5 6 7 -
(meters)
+2 µC
A +
B
C
D
E
F
+
+
+
+
+
-5 µC
-3 µC
-4 µC
+2 µC
+1 µC
-
-
-
-
-
-
©Modeling Workshop Project 2007 1 E2 Potential - ws 2 v3.3 JBS

3. Two books, initially on the floor, are picked up and placed on a shelf 2.0 m off the floor. One,
Twenty Other Things I Like To Do With That Stuff Between My Toes, has a mass of 1.0 kg. The
other, Why Physics Rules The Universe, has a mass of 2.0 kg. The gravitational field strength
near the surface of the Earth is approximately 10 N/kg.
a. Calculate the gravitational force acting on each book as it rests on the shelf. What factors
determine the size of this force
b. Calculate the change in the system’s gravitational potential energy as a result of picking each
book up off the floor and placing it on the shelf. What factors determine the size of this
change
c. What is the difference in gravitational potential (potential energy per unit mass) between the
floor and the shelf (Use data from each book to calculate this.) What factors determine the
size of this difference
d. How does gravitational potential differ from gravitational potential energy
©Modeling Workshop Project 2007 2 E2 Potential - ws 2 v3.3 JBS

4. Below are two parallel conducting plates, each carrying an equal quantity of excess charge of
opposite type. The plates are separated by 2.0 m.
(+)
(-)
1 µC 2 µC
2.0 m
Between the pair of plates are two positively charged
objects; the object on the left carries 1.0 µC of excess
charge, the object on the right carries 2.0 µC. The
electric field strength between the plates is uniform, and
approximately 10 N/C. You move each charge from
the negative plate to the positive plate. [For this
example, neglect the effects of the gravitational field.]
a. Calculate the electrical force acting on each object when it is between the plates. What
factors determine the size of this force
b. Calculate the change in the system’s electrical potential energy as a result of moving each
charge from the negative plate to the positive plate. What factors determine the size of this
change
c. What is the difference in electric potential (potential energy per unit charge) between each of
pairs of plates What factors determine the size of this difference
d. What is the difference in electric potential between the negative plate and a point midway
between the plates
e. How does electrical potential differ from electric potential energy
©Modeling Workshop Project 2007 3 E2 Potential - ws 2 v3.3 JBS

5. Rank the electrical potential difference for the following lettered objects in a uniform electric
field of 6 N/C between two charged walls. (Ignore gravitational effects.)
a. most ________ _________ ________ _________ _________ _________
b. Explain your ranking, stating why each is greater
+ 1 2 3 4 5 6 7 -
than, less than, or equal to its neighbors.
(meters)
+2 µC
A +
-
be given in V m . Show that these units are equivalent. B +
+2 µC -
C +
D +
-5 µC
-3 µC
-
-
E
-4 µC
+
-
+1 µC
F +
-
6. Rank the electrical potential at the positions of the lettered charges in a uniform electric field of
10 N/C between two charged walls. The negative wall potential has arbitrarily been designated
as 0 Volts.
a. most ________ _________ ________ _________ _________ _________
+ 1 2 3 4 5 6 7 -
b. Explain your ranking, stating why each is greater than,
(meters) 0 V
less than, or equal to its neighbors.
+2 µC
A +
-
B +
+2 µC -
C +
-5 µC
-
D -3 µC
+
E +
F +
-4 µC
+1 µC
-
-
-
7. The units for electric field were given as N . It turns out that the electric field strength can also
C
©Modeling Workshop Project 2007 4 E2 Potential - ws 2 v3.3 JBS