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Static Electricity

Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.

1.

What happens when a rubber rod is rubbed with a piece of fur, giving it a negative charge?
 a. Protons are removed from the rod. c. Electrons are added to the fur. b. Electrons are added to the rod. d. The fur is left neutral.

2.

A repelling force occurs between two charged objects when the charges are of
 a. unlike signs. c. equal magnitude. b. like signs. d. unequal magnitude.

3.

An attracting force occurs between two charged objects when the charges are of
 a. unlike signs. c. equal magnitude. b. like signs. d. unequal magnitude.

4.

When a glass rod is rubbed with silk and becomes positively charged,
 a. electrons are removed from the rod. c. protons are added to the silk. b. protons are removed from the silk. d. the silk remains neutral.

5.

Electric charge is
 a. found only in a conductor. c. found only in insulators. b. conserved. d. not conserved.

6.

If a positively charged glass rod is used to charge a metal bar by induction, the charge on the bar
 a. will be equal in magnitude to the charge on the glass rod. b. must be negative. c. must be positive. d. will be greater in magnitude than the charge on the glass rod.

7.

Charge is most easily transferred in
 a. nonconductors. c. semiconductors. b. conductors. d. insulators.

8.

In the diagram shown above, the circles represent small balls that have electric charges. Ball 1 has a negative charge, and ball 2 is repelled by ball 1. Next, you see that ball 2 repels ball 3 and that ball 3 attracts ball 4. What is the electric charge on ball 4?
 a. Ball 4 may have either a positive or negative charge. b. Ball 4 has a negative charge. c. Ball 4 has a positive charge. d. It is not possible to determine the charge on ball 4.

9.

The process of charging a conductor by bringing it near another charged object and then grounding the conductor is called
 a. contact charging. c. polarization b. induction. d. neutralization.

10.

Which of the following is not true for both gravitational and electric forces?
 a. The inverse square distance law applies. b. Forces are proportional to physical properties. c. Potential energy is a function of distance of separation. d. Forces are either attractive or repulsive.

11.

Two point charges, initially 2 cm apart, are moved to a distance of 10 cm apart. By what factor does the resulting electric force between them change?
 a. 25 c. b. 5 d.

12.

If the charge is tripled for two identical charges maintained at a constant separation, the electric force between them will be changed by what factor?
 a. c. 9 b. d. 18

13.

Electric field strength depends on
 a. charge and distance. c. Coulomb constant and mass. b. charge and mass. d. elementary charge and radius.

14.

Which of the following is not a characteristic of electrical potential energy?
 a. It is a form of mechanical energy. b. It results from a single charge. c. It results from the interaction between charges. d. It is associated with a charge in an electric field.

15.

When a positive charge moves in the direction of the electric field, what happens to the electrical potential energy associated with the charge?
 a. It increases. b. It decreases. c. It remains the same. d. It sharply increases, and then decreases.

16.

Two positive point charges are initially separated by a distance of 2 cm. If their separation is increased to 6 cm, the resultant electrical potential energy is equal to what factor multiplied by the initial electrical potential energy?
 a. 3 c. b. 9 d.

17.

Charge buildup between the plates of a capacitor stops when
 a. there is no net charge on the plates. b. unequal amounts of charge accumulate on the plates. c. the potential difference between the plates is equal to the applied potential difference. d. the charge on both plates is the same.

18.

When a capacitor discharges,
 a. it must be attached to a battery. b. charges move through the circuit from one plate to the other until both plates are uncharged. c. charges move from one plate to the other until equal and opposite charges accumulate on the two plates. d. it cannot be connected to a material that conducts.

19.

A 0.25 mF capacitor is connected to a 9.0 V battery. What is the charge on the capacitor?
 a. 1.2 ´ 10 C c. 2.5 ´ 10 C b. 2.2 ´ 10 C d. 2.8 ´ 10 C

20.

A 0.50 mF capacitor is connected to a 12 V battery. Use the expression PE = C(DV) to determine how much electrical potential energy is stored in the capacitor.
 a. 3.0 ´ 10 J c. 1.0 ´ 10 J b. 6.0 ´ 10 J d. 3.6 ´ 10 J

Problem

21.

What is the electric force between an electron and a proton that are separated by a distance of 1.0 ´ 10 m? Is the force attractive or repulsive? (e = 1.60 ´ 10 C, k = 8.99 ´ 10 N·m/C)

22.

What is the electric force between a proton and an alpha particle (charge 2e) that are separated by a distance of 3.0 ´ 10 m? (e = 1.60 ´ 10 C, k = 8.99 ´ 10 N·m/C)

23.

Two equal charges are separated by 3.7 ´ 10 m. The force between the charges has a magnitude of 2.37 ´ 10 N. What is the magnitude of q on the charges? (k = 8.99 ´ 10 N•m/C )

24.

A thundercloud has an electric charge of 43.2 C near the top of the cloud and –38.7 C near the bottom of the cloud. The magnitude of the electric force between these two charges is 3.95 ´ 10 N. What is the average separation between these charges? (k = 8.99 ´ 10 N·m/C)

25.

Two point charges having charge values of 2.0 mC and –4.0 mC, respectively, are separated by 1.5 cm. What is the value of the mutual force between them? (k = 8.99 ´ 10 N·m/C)

26.

Charge A and charge B are 2.2 m apart. Charge A is 1.0 C, and charge B is 2.0 C. Charge C, which is 2.0 C, is located between them and is in electrostatic equilibrium. How far from charge A is charge C?

27.

Two equal positive charges, both q = 2.0 ´ 10 C, interact with a third charge, Q = 4.0 ´ 10 C, as shown in the figure above. What is the magnitude of the electric force on Q? (k = 8.99 ´ 10 N·m/C)

28.

The diagram above shows four charges—A, B, C, and D— at the corners of a square. Charges A and D, on opposite corners, have equal charge, whereas both B and C have a charge of 1.0 C. If the force on B is zero, what is the charge on A?

29.

Two point charges are 10.0 cm apart and have charges of 2.0 mC and –2.0 mC, respectively. What is the magnitude of the electric field at the midpoint between the two charges?

30.

Charges of 4.0 mC and –6.0 mC are placed at two corners of an equilateral triangle with sides of 0.10 m. What is the magnitude of the electric field created by these two charges at the third corner of the triangle?