Lecture Quiz Questions With Solutions

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

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

-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. 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

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.

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

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

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

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

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

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

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:

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:

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

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

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

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

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

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

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

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

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

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

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