Download Name: Electrostatic Potential and Electric Energy – Practice 1

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Electrostatic Potential and Electric Energy – Practice
1. Spherical Conductor of Radius R and Charge +Q
A. Draw the electric field lines.
B. Draw the equipotential lines.
C. R = 1.00 cm and Q = +5.00 C,
i. What is E at r = 0.50 cm where r is the distance from the center of the sphere?
ii. What is E at r = 7.50 cm?
iii. What is V at r = 0.50 cm?
iv. What is V at r = 7.50 cm?
v. Find the work to move a charge q = +0.100 C from r = 7.50 cm to 4.50 cm.
vi. Find the work to move a charge q = +0.100 C from r = 7.50 cm at 0o with
respective to the +x axis to r = 7.50 cm at 120o.
2. Parallel Plate Conductors of Area A, Separation d and Charge Q
A. Draw the electric field lines in the
area between the plates.
B. Draw the equipotential lines in the
area a between the plates.
+Q
d
-Q
C. A = 400.0 cm2, Q = 25.0 C, and d = 0.1000 cm
i. Find  on the plates.
ii. What is E at a distance of 0.0300 cm above the bottom plate? [Hint: From a
Gauss’s Law standpoint, these can be considered to be thick plates.]
iii. What is E at a distance of 0.0900 cm above the bottom plate?
iv. What is the potential difference between the plates?
v. What is the potential at a distance of 0.0300 cm above the bottom plate
(assuming a potential of zero at the bottom plate)?
vi. What is the potential at a distance of 0.0900 cm above the bottom plate
(assuming a potential of zero at the bottom plate)?
vii. Find the work needed to move a charge q = +0.500 C from 0.0300 cm above
the bottom plate to 0.0900 cm above the bottom plate.
viii. Find the work needed to move a charge q = +0.500 C from 0.0300 cm above
the bottom plate on the left hand side to 0.0300 cm above the bottom plate
on the right hand side.
+Q
d
+q
-Q
3. A particular 12 V car battery can send a total charge of 84 A · h (ampere-hours) through a
circuit, from one terminal to the other.
A. How many coulombs of charge does this represent? [Hint: Consider the definition of
an ampere.]
B. If this entire charge undergoes a change in electric potential of 12 V, how much
energy is involved?
4. The electric potential difference between the ground and a cloud in a particular
thunderstorm is 1.2 × 109 V. In the unit electron-volts, what is the magnitude of the change
in the electric potential energy of an electron that moves between the ground and the cloud?
5. Two large, parallel, conducting plates are 12 cm apart and have charges of equal magnitude
and opposite sign on their facing surfaces. An electrostatic force of 3.9 × 10-15 N acts on an
electron placed anywhere between the two plates. (Neglect fringing.)
A. Find the electric field at the position of the electron.
B. What is the potential difference between the plates?
6. When an electron moves from A to B along an electric field line as shown, the electric field
does 3.94 × 10-19 J of work on it.
A. What are the electric potential differences VB - VA?
B. What are the electric potential differences VC - VA?
C. What are the electric potential differences VC – VB?
Solutions:
1.C. i. 0
ii. 7.99 x 106 N/C
iii. 4.50 x 106 V
iv. 5.99 x 105 V
v. 4.00 x 10-2 J
2.C. i. 6.25 x 10-4 C/m2
vi. 0
ii. 7.06 x 107 N/C
iii. 7.06 x 107 N/C
iv. 7.06 x 104 V
v. 2.12 x 104 V
3. A. 3.0 x 105 C
4. 1.2 x 109 eV
vi. 6.36 x 104 V
B. 3.6 x 106 J
vii. 2.12 x 10-2 J
viii. 0
5. A. 2.4 x 104 N/C
6. A. 2.46 V
B. 2.9 x 103 V
B. 2.46 V
C. 0