### Spring 2000 Physics 102 Hour Exam 1(31 questions)

The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***

This exam consists of 31 questions; true-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 131. When the exam was given, the minimum "A" score was 113; the minimum "B" was 99; the minimum "C" was 83; the minimum "D" was 65. The mean was 97.9; the median was 98. Click here to see the formula sheet that came with the exam.

### QUESTION 1***

A positive point charge q is placed near an uncharged conductor as shown to the right. What is the electric force on q?

(a)   toward the conductor
(b)   away from the conductor
(c)   zero

### QUESTION 2*

A negative charge is held along the midline equidistant from two equal positive charges. If the negative charge is released, in what direction does it move in the plane of the sheet? (Consider only electric forces)

(a)   vertically upward
(b)   vertically downward
(c)   horizontal to the right
(d)   horizontal to the left
(e)   it does not move

### QUESTION 3**

A uniform electric field is directed to the right as shown in the figure. Compare Wef the work required to move a positive charge from point e to point f, with Wgf, the work required to move the same charge from point g to point f.

(a)   Wef < Wgf
(b)   Wef = Wgf
(c)   Wef > Wgf

### QUESTION 4*

Four charges all of the same magnitude, are located at the corners of a square. Three are positive and one is negative as shown in the figure. What is the direction of the electric field at the center of the square, (marked with a dot in the figure)?

(a)   toward A
(b)   toward B
(c)   toward C
(d)   toward D
(e)   E = 0

### QUESTION 5**

After the circuit below has been connected for a very long time, what is the current IB?

(a)   IB = 0
(b)   IB = V/(2R)
(c)   IB = V/R

### QUESTION 6*

Two capacitors, one of capacitance C and the other of capacitance 2C are connected to an emf as shown below. Compare Q1 the charge on the positive plate of capacitor C with Q2 the charge on the positive plate of capacitor 2C.

(a)   Q1 < Q2
(b)   Q1 = Q2
(c)   Q1 > Q2

### QUESTION 7***

A parallel plate capacitor is charged by connecting it to a battery. The battery is then removed, leaving the charge on the capacitor plates. What happens to the energy stored in the capacitor when the plates are pulled a small distance further apart?

(a)   It decreases.
(b)   It stays the same.
(c)   It increases.

### QUESTION 8**

The light bulbs and batteries in the two circuits are identical. Compare B1 the total brightness produced by circuit 1, with B2 the total brightness produced by circuit 2.

(a)   B1 < B2
(b)   B1 = B2
(c)   B1 > B2

### QUESTION 9*

This and the next two questions are about the following situation:

The three charges indicated in the figure are fixed at the locations shown.

Calculate the electric potential at the origin assuming the potential is defined to be zero at infinity?

(a)   V = -18000 V
(b)   V = -9000 V
(c)   V = 0
(d)   V = +6000 V
(e)   V = +24000 V

### QUESTION 10**

Assume that the -6 mC and the +2 mC charges are already located at the positions shown. How much work is required to bring the +4 mC charge from infinitely far away to the location (0,-4) as shown in the figure?

(a)   W = -18.4 x 10-2 J
(b)   W = -4.2 x 10-2 J
(c)   W = 0
(d)   W = +3.6 x 10-2 J
(e)   W = +12.8 x 10-2 J

### QUESTION 11**

Suppose the -6 mC and the +2 mC charges are held fixed at the locations shown, but the +4 mC is released from the position (0,-4). Which way would it go?

(a)   to the left
(b)   to the right
(c)   it would remain at rest

### QUESTION 12*

This and the next question are about the following situation:

All charges have magnitudes as indicated and are fixed to the positions shown on the grid.

In which direction is the force on charge q3 due to charges q1 and q2 pointing?

(a)   to the left
(b)   to the right
(c)   down

### QUESTION 13**

What is the magnitude of this force?

(a)   F = 1.06 x 10-3 N
(b)   F = 2.31 x 10-3 N
(c)   F = 4.56 x 10-3 N
(d)   F = 11.3 x 10-3 N
(e)   F = 18.6 x 10-3 N

### QUESTION 14*

What is the effective resistance between points A and B?

(a)   R = 17.5 W
(b)   R = 20 W
(c)   R = 28.2 W
(d)   R = 30 W
(e)   R = 48.8 W

### QUESTION 15**

This and the next three questions are about the circuit to the right:

What is VTR, the electric potential difference between point T and point R?

(a)   VTR = 0 Volts
(b)   VTR = 40 Volts
(c)   VTR = 50 Volts
(d)   VTR = 60 Volts
(e)   VTR = 100 Volts

### QUESTION 16**

What is VPR, the electric potential difference between point P and point R?

(a)   VPR = 0 Volts
(b)   VPR = 40 Volts
(c)   VPR = 50 Volts
(d)   VPR = 60 Volts
(e)   VPR = 100 Volts

### QUESTION 17**

What is the direction of the current IPQ?

(a)   IPQ > 0 (Down)
(b)   IPQ = 0
(c)   IPQ < 0 (Up)

### QUESTION 18*

Calculate the current IB.

(a)   IB = 0 A
(b)   IB = 1.67 A
(c)   IB = 2.08 A
(d)   IB = 2.50 A
(e)   IB = 4.17 A

### QUESTION 19*

This and the next two questions are about the following situation:

Consider the circuit shown to the right.

Which of the following is a valid Kirchhoff voltage equation for the dotted outside loop?

(a)   E1 + I1R1 - E2 + I3R3 = 0
(b)   -E1 + I1R1 + E2 - I3R3 = 0
(c)   E1 - I1R1 - E2 - I3R3 = 0

### QUESTION 20*

Which of the following is a valid Kirchhoff current equation for node B?

(a)   I1+I2+I3 = 0
(b)   I1-I2-I3 = 0
(c)   I1-I2+I3 = 0

### QUESTION 21**

The circuit elements have the values shown in the table to the right.

Calculate VAB = VA- VB, the potential difference between point A and point B?

(a)   VAB = -20 Volts
(b)   VAB = -10 Volts
(c)   VAB = 0 Volts
(d)   VAB = +10 Volts
(e)   VAB = +20 Volts

### QUESTION 22*

This and the next two questions are about the following situation:

A battery of emf 16 volts is connected to a parallel plate capacitor. The points marked a and b are specific locations on the conducting wire of the circuit. The dotted surface marked c is located exactly halfway between the plates of the capacitor.

What is the direction of the electric field between the plates of the capacitor?

(a)   upward
(b)   downward

### QUESTION 23*

What is the potential difference between point b and point a on the circuit?

(a)   16 V
(b)   8 V
(c)   0 V

### QUESTION 24**

What is the potential difference between surface c and point a on the circuit?

(a)   16 V
(b)   8 V
(c)   0 V

### QUESTION 25*

This and the next three questions are about the following situation:

In the circuit shown below, the battery emf is 12 volts, the resistors R1 = 3 W, R2 = 3W, and the capacitor C = 6 mF. The capacitor is initially uncharged. The circuit is connected as shown below, then switch S1 is closed, while S2 is left open.

Immediately after switch S1 is closed, what is the current in resistor R1?

(a)   I1 = 0 A
(b)   I1 = 2 A
(c)   I1 = 4 A

### QUESTION 26*

Immediately after switch S1 is closed, what is the current in resistor R2 ?

(a)   I2 = 0 A
(b)   I2 = 2 A
(c)   I2 = 4 A

### QUESTION 27*

After a long time, switch S1 is opened, and switch S2 is closed.

After switch S2 is closed, what happens to the charge on capacitor C?

(a)   The capacitor discharges through resistor R1.
(b)   The capacitor discharges through resistor R2.
(c)   The capacitor discharges through resistors R1 and R2.

### QUESTION 28*

After switch S1 is opened and S2 is closed, which of the following two graphs correctly describes the behavior of the voltage across the capacitor as a function of time? (The time t = 0 is just after S2 is closed)?

(a)
(b)
(c)

### QUESTION 29*

This and the next two questions are about the following situation:

Three capacitors are connected to an emf as shown in the diagram. The value of the emf is 12 volts, while C1 = 7 mF, C2 = 9 mF, and C3 = 5 mF.

What is Q1, the charge on the capacitor C1?

(a)   Q1 = 6.0 x 10-5 C
(b)   Q1 = 8.4 x 10-5 C
(c)   Q1 = 10.8 x 10-5 C
(d)   Q1 = 14.4 x 10-5 C
(e)   Q1 = 16.8 x 10-5 C

### QUESTION 30**

What is V3, the potential difference across the plates of capacitor C3?

(a)   V3 = 4.3 V
(b)   V3 = 5.0 V
(c)   V3 = 6.2 V
(d)   V3 = 7.0 V
(e)   V3 = 7.7 V

### QUESTION 31*

What is Utotal, the total energy stored in all of the capacitors?

(a)   Utotal = 2.31 x 10-4 J
(b)   Utotal = 3.87 x 10-4 J
(c)   Utotal = 5.04 x 10-4 J
(d)   Utotal = 7.35 x 10-4 J
(e)   Utotal = 9.81 x 10-4 J

Scoring of True-False (T,F) Questions:
• If you mark the correct answer, you get 2 points.
• If you mark the wrong answer or if you mark neither answer, you get 0 points.
Scoring of Multiple Choice I (a,b,c) Questions:
• If you mark the correct answer, you get 3 points.
• If you mark a wrong answer or if you mark none of the answers, you get 0 points.
Scoring of Multiple Choice II (a,b,c,d,e) Questions:
• If you mark one answer and it is the correct answer, you get 6 points.
• If you mark two answers and one of them is the correct answer, you get 3 points.
• If you mark three answers and one of them is the correct answer, you get 2 points.
• If you do not mark the correct answer, or if you mark more than three answers, or if you mark none of the answers, you get 0 points.