Transcript Document

Lecture Quiz Questions
With Solutions
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
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
Before
+2Q
After
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
Before
None of the above
+2Q
After
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
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
1.
2.
3.
4.
5.
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?
M
L
+4C
0C
+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?
M
L
+4C
1.
2.
3.
4.
5.
4C
2C
1C
0C
None of the above
N
-2 C
0C
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?
M
L
+4C
1.
2.
3.
4.
5.
4C
2C
1C
0C
None of the above
N
-2 C
0C
Example:
Equipotential
Surfaces
C
•
B•
•
A
• At which position (A, B, or
C) does the electric field
have the greatest
magnitude?
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?
(a)0
(b)−Q
Q
(c)−3Q
-3Q
(d)+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?
(a)0
(b)−Q
(c)-3Q
Q
(d)+3Q
-2Q
4Q
A
B
C
R
L
R
L
Three sections of different copper
wires are shown. Order them in
increasing resistance.
1. A < B < C
2. A = C < B
3. C < A < B
4. C < A = B
5. A = B = C
2R
2L
Practice:
A
B
C
R
L
R
L
Three sections of different copper
wires are shown. Order them in
increasing resistivity.
1. A > B > C
2. A = C > B
3. C > A > B
4. C > A = B
5. A = B = C
2R
Quiz:
2L
Practice:
Each bulb has a resistance of 10 Ω. What is
the equivalent resistance of the circuit?
1. 40 Ω
2. 20 Ω
3. 16 ⅔ Ω
4. 2 ½ Ω
V
Practice:
Each capacitor has a capacitance of 10 F.
What is the equivalent capcitance of the
circuit?
1. 30 F
2. 20 F
3. 6 ⅔ F
4. 3 ⅓ F
V
Quiz:
R
ε
A
R
B
ε
R
Order the circuits by equivalent
resistance from smallest to
largest.
A.
B.
C.
D.
A<B<C
C<B<A
B<A<C
B<C<A
R
C
ε
R
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. 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. 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?
A.Attractive
I
1
r
L
B.Repulsive
2
C.There is no force.
D.I don’t know.
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?
A.Clockwise
B.Counter-clockwise
C.There is no current
D.I don’t know
v
S
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?
A.τ ln(⅓)
B. 3 τ
C. τ ln(3)
D.⅓ τ
Quiz:
Rank the maximum, average,
and RMS values of M.
A.
B.
C.
D.
Mrms < Mave < Mmax
Mave < Mrms < Mmax
Mmax < Mrms < Mave
Mave < Mmax < Mrms
M
+Mmax
-Mmax
Section 22.1
Quiz:
Rank the maximum, average,
and RMS values of M.
A.
B.
C.
D.
Mrms < Mave < Mmax
Mave < Mrms < Mmax
Mmax < Mrms < Mave
Mave < Mmax < Mrms
M
Mmax
Section 22.1