1. Lecture Quiz Questions
With Solutions

2. Two charges, -Q and +2Q are placed a distance R apart
Two charges, -Q and +2Q are placed a distance R apart. The magnitude and direction of the force F on the -Q charge is shown by the arrow. Which of the following arrows represents the approximate magnitude and direction of the force on the +2Q charge? -Q
+2Q
None of the above 1 2 3 4 5 6

3. Two charges, -Q and +2Q are initially placed a distance R apart
Two charges, -Q and +2Q are initially placed a distance R apart. The magnitude and direction of the force F on the -Q charge is shown by the arrow in the “Before” picture. Next, the –Q charge is changed to +2Q. Which of the following arrows represents the approximate magnitude and direction of the new force on the bottom +2Q charge?
+2Q -Q
+2Q
+2Q
Before
After

4. -Q -Q +2Q After +2Q Before None of the above
Two charges, -Q and +2Q are initially placed a distance R apart. The magnitude and direction of the force F on the -Q charge is shown by the arrow in the “Before” picture. The charges are then moved to a separation distance of R/2. Which arrow’s direction and length represents the new force on the +2Q charge? -Q -Q
+2Q
+2Q
After
Before
None of the above

5. 5. The net electric force is zero at point 1
What is the direction of the electric force on a negative test charge at point 1? 1 1. 2. 3. 4.
5. The net electric force is zero at point 1

6. A and in the direction of the field lines.
At which point, A or B, will the magnitude of the acceleration of a negative test charge be greater if the charge is released from rest, and which way will it go?
E Field Lines
A and in the direction of the field lines.
A and opposite to the field line directions.
B and in the direction of the field lines.
B and opposite to the field line directions.
The accelerations are the same.

7. PRACTICE: Two identical metal balls L and M initially have charge 4 C and 0 C, respectively, as shown below. What is the charge on M after you let L touch M and set them apart? L M
+ 4 C
0 C
+2 C

8. Quiz: (1 pt. participation) Three identical metal balls L, M and N initially have charge 4 C, -2 C and 0 C, respectively, as shown below. What is the charge on N after you let L first touch M, and then remove L and let M touch N? L M
+ 4 C
-2 C N
0 C
4 C
2 C
1 C
0 C
None of the above

9. QUIZ: (1pt. participation, 1 pt
QUIZ: (1pt. participation, 1 pt. correct) Three identical metal balls L, M and N initially have charge 4 C, -2 C and 0 C, respectively, as shown below. What is the charge on N after you let L first touch N, and then remove L and let M touch N? L M
+ 4 C
-2 C N
0 C
4 C
2 C
1 C
0 C
None of the above

10. Example:
At which position (A, B, or C) does the electric field have the greatest magnitude?
Equipotential
Surfaces A B C

11. A charged, metal object has a cavity inside it into which is placed two charges, one of Q and the other of −3Q. There is a net charge of −Q on the object itself. What is the net charge on the outside surface of the metal object? −Q
−3Q
+3Q Q
-3Q -Q

12. A charged, metal object has a cavity inside it into which is placed two charges, one of Q and the other of −2Q. There is a net charge of −Q on the object itself. What is the net charge on the outside surface of the metal object? −Q
-3Q
+3Q Q
-2Q 4Q

13. A B C R L R L
Three sections of different copper wires are shown. Order them in increasing resistance.
A < B < C
A = C < B
C < A < B
C < A = B
A = B = C
2 L
2 R
Practice:

14. A B C R L R L
Three sections of different copper wires are shown. Order them in increasing resistivity.
A > B > C
A = C > B
C > A > B
C > A = B
A = B = C
2 L
2 R
Quiz:

15. Practice:
Each bulb has a resistance of 10 Ω. What is the equivalent resistance of the circuit? V
40 Ω
20 Ω
16 ⅔ Ω
2 ½ Ω

16. Practice:
Each capacitor has a capacitance of 10 F. What is the equivalent capcitance of the circuit? V
30 F
20 F
6 ⅔ F
3 ⅓ F

17. Quiz: R ε A B ε R R
Order the circuits by equivalent resistance from smallest to largest.
A < B < C
C < B < A
B < A < C
B < C < A C R ε

18. PRACTICE: A circuit is shown in the circuit diagram below contains three identical resistors (R1 = R2 = R3) of 100 Ω resistance. What is the equivalent resistance of the three resistors?
a) 33 Ω b) 50 Ω c) 150 Ω d) 300 Ω

19. PRACTICE: A circuit is shown is the same as before
PRACTICE: A circuit is shown is the same as before. The battery has an emf of 1.5 V. What is the current through R1?
a) 10 mA b) 15 mA c) 225 A d) 1500A

20. QUIZ: A circuit is shown is the same as before
QUIZ: A circuit is shown is the same as before. What is the potential difference across R1?
a) 0.5 V b) 1.0 V c) 1.5 V d) 3.0 V

21. Example: Two Parallel Wires
Is the force on wire 1 due to wire 2 attractive or repulsive?
Attractive
Repulsive
There is no force.
I don’t know. I 1 L r 2 I

22. Example: Falling Magnet
Suppose a bar magnet falls upward through a loop of wire, south pole first. What is the direction of the induced current?
Clockwise
Counter-clockwise
There is no current
I don’t know S v

23. Quiz: RL Circuit
An RL circuit has resistance R and inductance L. How long does it take for the voltage in the inductor to decrease to 1/3 of its maximum value?
τ ln(⅓)
3 τ
τ ln(3)
⅓ τ

24. Quiz: M Rank the maximum, average, and RMS values of M.
Mrms < Mave < Mmax
Mave < Mrms < Mmax
Mmax < Mrms < Mave
Mave < Mmax < Mrms
+Mmax
-Mmax M
Section 22.1

25. Quiz: M Rank the maximum, average, and RMS values of M.
Mrms < Mave < Mmax
Mave < Mrms < Mmax
Mmax < Mrms < Mave
Mave < Mmax < Mrms M
Mmax
Section 22.1