# worksheet-Electrostatics-Unit-Review

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```					Name _______________________________________               Period ________      Date _________________

Pre-IB Accelerated Science Electrostatics Unit Review
Electric Forces and Fields

1. There are two kinds of electric charge: they were first named _______________ and ______________
by Benjamin Franklin.
2. Unlike gravity, the other field force that we have studied, the electric force can either be attractive or
repulsive. The general rule is that ______________ charges attract, while _____________ charges
repel.
3. An electrical ____________ is a material in which electrons are loosely held, and an ______________
is a material that has few mobile electrons.
4. Complete the following table regarding methods by which charge can be transferred:

Method of                   Definition                  Example          Applicable to     Applicable to
charging                                                                Conductors?        Insulators?
Contact

Friction

Induction

Charge
polarization

5. Most matter has a neutral/positive/negative charge by nature. Explain what this means based on the
relative numbers of charged particles contained in a quantity of matter. ________________________.
6. With respect to subatomic particles, negative charge is due to __________________, while positive
charge is due to ________________.
7. When a rubber rod is rubbed with fur or wool, the rubber rod acquires a residual _____________
charge. The fur or wool is left with a residual ____________________ charge. Compare the
magnitude of the net negative and positive charges of the two bodies: _________________________.
8. When a glass or plastic rod is rubbed with silk, it becomes __________________ charged. The silk is
left with a net _______________ charge.
9. Describe the steps involved in producing a positive charge on a conductor by the process of induction:
__________________________________________________________________________________
_________________________________________________________________________________.
10. The electric and gravitational forces have several similarities and differences. Name two similarities
and two differences between them. _____________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
Name _______________________________________                  Period ________       Date _________________

11. Coulomb’s Law describes mathematically the magnitude of the electric force between two point
charges (or larger charged bodies that are separated by a large distance. Write the expression for
Coulomb’s Law: Felectric = _______________________. The electric force is _________________
proportional to the product of the ______________ and inversely proportional to the square of the
_____________________ between them. The constant of proportionality, Coulomb’s constant, has a
value of ________________________ Nm2/C2. Be able to predict what will happen to the electric
force between two charges if the magnitude of either one or both change, or if the distance between
them changes.
12. The electric force is a vector quantity, which means that it has both magnitude and direction. The
magnitude of the force is found using the _______________________ of the charges. The direction is
found based on the principle that __________ repel and unlike charges ____________________. The
direction of the force between two charges is along the straight line between them.
13. When more than two electric charges are present, the net force on any of them can be found using the
principle of _________________________, which means, in the case of vectors, that you can add the
individual forces together using vector addition. In general, this means that we must resolve the force
vectors into_____________________, then find the ______________________ using the
Pythagorean Theorem.
14. The forces on a given charge are in equilibrium when their vector sum equals _____________. It is
important to keep track of the sign of the force.
15. The electric field is defined as the electric ___________ per unit of _____________. It has units of
____________________.
16. By convention, the direction of the electric field is defined as _______________________________
________________________________________________________________________________.
17. The strength of the electric field from a point charge is E = _____________________. The charge q in
this expression is the charge that produces the field. Note that the field strength at a point in space
depends on the charge that sets up the field and the distance from that charge.
18. Since the electric field is a vector quantity, the electric field strength at a point due to two or more
charges can be found by _____________________________________________________________.
19. Electric field lines help us visualize electric field patterns, and the strength and direction of the electric
field at different points in space. The number of lines is proportional to ________________________.
20. By convention, electric field lines always begin on and are directed away from __________________
charges, and are directed toward and terminate on ____________________ charges.
21. A conductor in electrostatic equilibrium has the following properties:
a.
b.
c.
d.

Electrical Potential Energy
22. Electrical potential energy is a form of __________________ energy. We learned how to find the
magnitude of the electrical potential energy for two configurations. First, for a charge in a uniform
electric field of strength E, the electrical potential energy can be found using the following expression:
PEelectric = _________________. Remember that by convention if the charge’s displacement is in the
same direction as the field, it is _______________. The negative sign shows that the electrical
potential energy will _______________ if the charge is negative and __________________ if the
charge is positive (assuming that the displacement is positive).
23. A change in potential energy for this case is simply PEelectric = ___________.
Name _______________________________________ Period ________ Date _________________
24. The other case we considered for electrical potential energy was that for a pair of charges. In this case
PEelectric = ____________________. For this case, the reference point for the electrical potential
energy is assumed to be at ____________________. The electrical potential energy is ____________
for like charges and _________________ for unlike charges. Because of the assumption about
reference point, the expression for the electrical potential energy for two charges and the change in
potential energy have the same form.
25. The electric potential at some point is defined as __________________________________________
_________________________________: V = __________________________.
26. Potential difference, or voltage, is a measure of the change in the electrical potential energy divided by
the charge. The unit for electric potential and potential difference is the ___________, which is
equivalent to a _______________ per _________________ of charge.
27. We can use the previous expressions for electrical potential energy to find the potential difference in a
uniform field: ______________________________ and the potential difference between a point at
infinity and a point near a point charge: ___________________________________.
28. Since the electric potential and potential difference are scalar quantities, we find the potential
difference at a point near a number of charges simply by ___________________________________.

Review Problems
(kC = 8.99 × 109 N.m2/C2; 0 = 8.85 × 10–12 C2/N.m2)

1. The force between two equal charges has a magnitude of 1.56 × 10–3 N. If the separation between the charges is
7.6 × 10–9 m, what is the value of q on the charges?

2. Two objects are separated by a distance of 8.50 cm. One of the objects has a charge of 7.7 µC, and the other
object has an equal but opposite charge. What is the magnitude of the electric force on the objects?

3. Three point charges of magnitude 3.5 × 10–11 C are arranged in a straight line along the x-axis. The charges are
spaced 1.75 m apart. What is the resultant magnitude and direction of the force on the rightmost charge?

4. A charge of 8.20 nC is located 83.0 cm from a charge of 7.10 nC. At what position, P, will a charge of –4.50 nC
be in electrostatic equilibrium? Specify the position relative to the 8.20 nC charge.

5. An electric field of 2535 N/C is produced by a charge of 7.25 × 10–12 C. For this field strength, what is the
distance to the charge?

6. A charge of 7.50 mC is located at the origin, and a second charge of 2.50 mC is located 1.50 m from the origin
on the x-axis. What is the magnitude and direction of the electric field at 3.00 m away from the origin on the x-axis?

7. Four charges are located at the corners of a square. Charges B and C are equal and charges A and D are both +1
C. If there is no net force on charge C, what is the charge on C?
Name _______________________________________                      Period ________        Date _________________
8. A 27 µC charge moves 39.0 cm in the same direction as a uniform electric field with a magnitude of 177 N/C.
What is the change in the electrical potential energy of the charge?

9. A charge of 0.50 C is placed at the North Pole of Earth, and a charge of –1.5 C is placed at the South Pole of
Earth. What is the electrical potential energy for this pair of charges? Earth has a radius of 6.37 × 106 m.

10. A glass rod gains a +3.70 µC charge when rubbed with silk. The electric potential energy found when the glass
rod and the silk are held at a distance from each other is –9.3 × 10–3 J. What is the distance between the rod and the
silk?

11. A uniform electric field of magnitude 3.3 × 104 N/C is between two plates separated by a distance of 0.77 cm.
What is the magnitude of the potential difference between the plates?

12. The electric potential at an unknown distance from a charge of 7.5 nC is 48.0 V. What is the distance from the
charge?

13. What is the potential difference between a point 0.55 mm from a charge of 3.8 nC and a point at infinity?

14. A charge of 3.04 × 10–18 C is located 1.42 × 10–10 m from the origin along the y-axis. A second charge of 2.72 ×
10–18 C is located –1.65 × 10–10 m from the origin along the y-axis. What is the electrical potential at the origin?

15. Four charges are located on the circumference of a circle of 75.0 cm radius. The charges are 7.5 µC, 2.5 µC, –
5.0 µC, and –7.5 µC. What is the total potential difference between the center of the circle and infinity? (Hint: Use
the superposition principle.)

16. A uniform electric field E of 1000 V/m is directed parallel to positive x axis. If the electric potential 10 meters
from the origin is 2000 V, what is the potential at a distance of 5 m from the origin?

Review Problems Key:
1. 3.2 × 10-15 C
2. 74 N
3. 4.5 × 10-12 N in the positive direction along the x-axis
4. 0.432 m to the right of the 8.20 nC charge and directly between the charges
5. 5.07 × 10-3 m
6. 1.75 × 107 N/C along the x-axis
7. – 2.8 C
8. -1.9 × 10-3 J
9. -5.3 × 102 J
10. 1.3 × 101 m
11. 250 V
12. 1.4 m
13. 6.2 × 104 V
14. 340 V
15. -3.0 × 104 V
16. 7000 V

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