1. If the distance between two charges is reduced to one-half its initial value, the force between them will be changed to

a. one-half its initial value.

b. one-fourth its initial value.

c. twice its initial value.

d. four times its initial value.

2. The lines of force produced by a dipole are directed

a. radially outward.

b radially inward.

c. from the positive to the negative charge.

d. toward the equilateral surface.

3. Two charges, when separated by a distance R, produce a force F on each other. If the separation is increased to 1.7R, what is the new force?

a. 0.12F

b. 0.35F

c. 0.60F

d. 2.9F

4. The electric field at a distance of 22.0 m from a point charge is found to be 150 N/C. What is the magnitude of the charge?

a. 1.7 C

b. 8.0 C

c. 21 C

d. 33 C

5. Electric charges of the same sign

a. also have the same magnitude.

b. exert no forces on each other.

c. attract each other.

d. repel each other.

6. Which of the following is not true about electric field lines?

a. The number of electric field lines is proportional to the size of the charge.

c. The electric field lines start on positive charges and end on negative charges.

7. Charge q₁ = 2.8 microC is placed at the origin and charge q₂ = -8.4 microC is placed on the x-axis at x = -20 cm as shown in the sketch. Where along the x-axis can a third charge q₃ = -7.4 microC be placed such that the resultant force on this third charge is zero?

8. Four charges are fixed to the corners of a square of side length 5 mm as shown in the diagram below. What is the net force (magnitude and direction) on the -2 microC charge?

1. The electron volt (eV) is a unit of

a. mass

b. capacitance

c. potential difference

d. energy

2. Lines of force and equipotential surfaces are always

a. curved.

b. straight.

c. perpendicular to each other at every point.

d. parallel to each other at every point.

3. Two parallel metal plates are separated by 2.5 cm and have a potential difference of 3000 V between them. What is the electric field between the plates?

a. 830 N/C

b. 4500 N/C

c. 7500 N/C

d. 1.2 x 10‡ N/C

4. A capacitor is to be constructed with parallel plates separated by 2.5 mm and is to have a capacitance of 1.0 æF. Calculate the area of each plate.

a. 280 m‚

b. 85 m‚

c. 19 m‚

d. 2.4 m‚

5. The capacitor in a photographer's strobe light has a capacitance of 150 microF and is charged to 330 V. How much energy does it contain?

a. 5.0 J

b. 8.2 J

c. 37 J

d. 48 J

6. If a thin sheet of plastic is inserted between the plates of a parallel plate capacitor without changing the plate separation, the capacitance will

a. not change.

b. decrease.

c. increase.

d. increase or decrease depending on the thickness.

7. If several capacitors of different capacitances are connected in series and connected to a battery, then

a. the charge on each will be proportional to its capacitance.

b. the potential across each will be proportional to its capacitance.

c. all will have the same charge.

d. all will have the same potential.

8. If the area of the plates of a parallel-plate capacitor is doubled, the capacitance will

a. quadruple.

b. double.

c. be cut in half.

d. remain unchanged.

9. If the potential difference of a capacitor is doubled, the energy stored in that capacitor is

a. doubled.

b. halved.

c. quartered.

d. quadrupled.

10. A parallel plate capacitor has square plates that are 1.5 m x 1.5 m and are separated by 1 mm. The space between the plates is filled with glass having a dielectric constant of 6.2.

a. Calculate the capacitance of this capacitor.

b. What is the maximum voltage that can be put on the capacitor?

c. What is the maximum energy that can be stored on the capacitor?

11. A parallel-plate air capacitor is made from two square plates measuring 14 cm on a side, spaced 5.3 mm apart. What must the potential difference between the plates be to produce an energy density of 0.044 J/m„?

12. The potential at a certain distance from a point charge is 600 V, and the electric field is 200 N/C.

a. What is the distance to the point charge?

b. What is the magnitude of the charge?

13. Three charges -2 nC, 3 nC, and 4 nC are arranged at the points of an equilateral triangle whose side is 10 cm. What is the potential energy of the system?

14. Is work done when a charge moves along an equipotential surface? Explain.

15. Draw both the equipotential surfaces and the electric field lines for a parallel-plate capacitor with a potential difference of 5 volts between the plates.