13 Problems on electrostatics and current

1, True/False questions: State, in complete sentences, why your answer is wrong.

2, Multiple choice concept questions: Determine the correct answer and state, in complete sentences, why your answer was wrong and why the correct answer is correct.

3, Multiple choice problem questions: Determine the correct answer by working the problem correctly. Show your work. No credit will be given for answers not supported by your work.

Test Questions

2, Which of the following is not true about the electric potential, V?
a, V at a point is the electric potential energy per unit charge at that point.
b, We are normally only interested in difference in potential.
c, V is a vector so it s direction must be considered.
d, The units of V may be expressed as Joule/Coulomb.
My answer was D and the other students got C.

4, If you bring a negatively charged insulator near two metallic spheres that are in contact as shown and then separate the spheres (with an insulator), the sphere on the right will have:
A. no net charge.
B. a positive charge.
C. a negative charge
D. either a positive or negative charge.
E. none of the above
My answer was C the other students got B.

5. Three charges +q, +Q, and -Q are placed at the corners of an equilateral triangle. The net force on charge +q due to the other charges (the magnitudes of +Q and -Q are the same is.
A. vertically up
B. vertically down
C. zero
D.horizontal to the right
E. horizontal to the left.
My answer was A the other students got D.

7. If non-electric forces are negligible, the electric potential energy of a charged particle released from rest in an electric field.
A. increases
B. decreases
C. is conserved
D. increases or decreases depending on the sign of the charge
My answer was C and the other students got B.

9. A point charge q sets up an electric field E at the position of another charge q; the force exerted by E on q' is independent of the magnitude of q'
My answer was True the other students marked False.

15. If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit will
A. double
B. increase by a factor of four
C. decrease by one-half
D. decrease by a factor of four
My answer was B the other students got C.

16. When two or more resistors ( of different resistances) are connected in series with a battery.
A. the voltage drop across each resistor is the same
B. the current through each resistor is the same
C. the power dissipated by each resistor is the same
D. all of the above
E. none of the above
My answer was D the other students got B.
Reading this question again out of a stressful environment, I know the answer was B.

21. A battery is connected to a series combination of a switch, a resistor, and an initially uncharged capacitor. The switch is closed at t=0. As the charge on the capacitor increases.
A. the current increases
B. the electric field inside the capacitor decreases
C. the current remains constant
D. the voltage drop across the capacitor decreases
E. the voltage drop across the resistor decreases
My answer was C the other students got E.

22. The capacitance of a charged capacitor is directly proportional to the charge.
My answer was True the other students got False.

23. A 200-Micro-Farad capacitor is charged to 200V and is then discharged across a 100ohm resistor. The time constant for this circuit is approximately
a. 20ms
b. 40ms
c. 10ms
d. 30ms
e. 15m
My answer was B the other students got A.

24. A charged parallel-plate capacitor is disconnected from a battery, and the plates are pulled a small distance further apart. For the following quantities, indicate where they increase, decrease, or stay the same.
A. Q stay the same
B. E Between the plates stays the same ( This one was wrong)
C. Energy stored in the capacitor increase

25. A current reading is obtained by properly placing an ammeter ( a real one, not an ideal one) in a circuit consisting of one resistor and a battery. As a result,
A. the voltage drop across the resistor increases
B. the current flowing in the circuit increases.
C. The current flowing in the circuit decreases
D. The current flowing in the circuit does not change
My answer was D the other students got C.

28. An ideal voltmeter has a very large internal resistance.
My answer was False the other students put True.