### Fall 2001 Physics 102 Hour Exam 1(30 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 30 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 132. When the exam was given, the mean was 96.0; the median was 99. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

This and the following two questions pertain to the following situation.

Four point charges are arranged in the configuration below. Each grid is 1 m.

Calculate the x-component of the net electric field at (0,2) due to the four charges shown.

(a)   Ex = 3.9 × 103 N/C
(b)   Ex = 1.6 × 103 N/C
(c)   Ex = 0 N/C
(d)   Ex = -1.6 × 103 N/C
(e)   Ex = -3.9 × 103 N/C

### QUESTION 2*

Calculate the y-component of the net electric field at (0,2) due to the four charges shown.

(a)   Ey = -8.1 × 103 N/C
(b)   Ey = -3.9 × 103 N/C
(c)   Ey = 0 N/C
(d)   Ey = 3.9 × 103 N/C
(e)   Ey = 8.1 × 103 N/C

### QUESTION 3*

What is the approximate magnitude of the electric force on a point charge (-3 mC) located 100 m away from the origin?

(a)   1.0 × 10-5 N
(b)   2.2 × 10-5 N
(c)   4.7 × 10-5 N
(d)   9.2 × 10-5 N
(e)   1.4 × 10-4 N

### QUESTION 4**

This and the following question pertain to the following situation.

Four point charges are arranged in the configuration below. The separation between each pair of grid points is 1 meter.

Calculate the electric potential at the origin due to the four charges.

(a)   7.1 × 104 V
(b)   4.0 × 104 V
(c)   0 V
(d)   2.1 × 104 V
(e)   8.1 x104 V

### QUESTION 5*

How much work did it require to assemble the charges by bringing them from infinity?

(a)   1.20 J
(b)   0.70 J
(c)   0.25 J
(d)   0.12 J
(e)   0.42 J

### QUESTION 6*

At a distance of 0.5 m from a point charge, the electric potential is -100 V. What is the potential at a distance of 0.25 m ?

(a)   -50 V
(b)   -100 V
(c)   -200 V

### QUESTION 7*

Choose the charges Q1 and Q2 that are consistent with the configuration of the electric fields that is shown in the adjacent schematic diagram.

(a)   Q1 = 3 mC, Q2 = -3 mC
(b)   Q1 = -8 mC, Q2 = 4 mC
(c)   Q1 = 8 mC, Q2 = 4 mC
(d)   Q1 = 2 mC, Q2 = -1 mC
(e)   Q1 = -2 mC, Q2 = 3 mC

### QUESTION 8**

There is a conducting sphere in the middle of two charged, parallel conducting plates as shown. Which electric field line distribution describes the effect of the conducting sphere better?

(a)
(b)
(c)

### QUESTION 9*

Two small spheres with equal masses m are suspended by strings of length 1 meter as shown. Each string makes an angle of 30° with the vertical in equilibrium. (g = 9.8 m/s2)

In equilibrium, which one of the following statements is true?

(a)   Q1 and Q2 must have the same magnitudes.
(b)   Q1 and Q2 must have the opposite charges.
(c)   Q1 must be a positive charge.

### QUESTION 10**

The figure shows a group of equipotential lines of the electric potential, which result from a charge distribution in the plane of the paper. At which location will an electron (q = -1.6 × 10-19 C) experience a force directed toward the bottom of the screen?

(a)
(b)
(c)

### QUESTION 11**

This and the following question pertain to the following situation.

What is the difference in electric potential between a and b?

(a)   Electric potential is higher at a by 1.1 × 103 V.
(b)   Electric potential is higher at b by 1.1 × 103 V.
(c)   Electric potential is higher at a by 1.3 × 103 V.
(d)   Electric potential is higher at b by 1.3 × 103 V.
(e)   Zero.

### QUESTION 12**

A student moves a charge of -2 coulombs along the path indicated from b to c to a, and then back to b. How much work has the student performed?

(a)   2.2 × 10 J
(b)   4.4 × 10 J
(c)   2.6 × 10 J
(d)   5.2 × 10 J
(e)   zero

### QUESTION 13*

This and the following three questions pertain to the following situation.

Compare I3, the current through resistor 3, with I4, the current through resistor 4.

(a)   I3 > I4
(b)   I3 = I4
(c)   I3 < I4

### QUESTION 14*

Compare V1, the voltage across resistor 1, with V5, the voltage across resistor 5.

(a)   V1 > V5
(b)   V1 = V5
(c)   V1 < V5

### QUESTION 15*

How much power is being delivered by the battery?

(a)   P = 23.4 W
(b)   P = 37.1 W
(c)   P = 48.8 W
(d)   P = 62.7 W
(e)   P = 75.2 W

### QUESTION 16**

What is I2, the current through resistor 2 ?

(a)   I2 = 0.27 A
(b)   I2 = 0.45 A
(c)   I2 = 1.32 A
(d)   I2 = 2.95 A
(e)   I2 = 3.17 A

### QUESTION 17*

Identical 25 watt bulbs are placed in circuits (circuit I and circuit II) with identical batteries as shown below.

(a)   An individual bulb is brighter in circuit I than in circuit II.
(b)   An individual bulb is brighter in circuit II than in circuit I.
(c)   The brightnesses of all of the bulbs are the same.

### QUESTION 18***

In the circuit shown below (note that the resistances of these bulbs may not be the same),

(a)   the 25 watt bulb and the 100 watt bulb have the same brightness.
(b)   the 25 watt bulb is brighter than the 100 watt bulb.
(c)   the 100 watt bulb is brighter than the 25 watt bulb.

### QUESTION 19*

This and the following two questions pertain to the following situation.

Which of the following is a valid equation that describes the voltage changes around the closed loop that is indicated by the arrows?

(a)   -E1 + I1R1 - I4R4 + E4 = 0
(b)   +E1 + I1R1 - I4R4 - E4 = 0
(c)   -E1 + I1R1 - I4R4 - E4 = 0
(d)   -E1 + I1R1 + I4R4 + E4 = 0
(e)   +E1 - I1R1 - I4R4 + E4 = 0

### QUESTION 20*

Which of the following is a valid equation that describes the current in the above circuit?

(a)   I1 + I2 + I3 + I4 = 0
(b)   I1 - I2 - I3 + I4 = 0
(c)   I1 + I2 - I3 - I4 = 0

### QUESTION 21**

What is the magnitude of the potential difference between points A and B ?

(a)   |VAB| = 0 volts
(b)   |VAB| = 10 volts
(c)   |VAB| = 20 volts
(d)   |VAB| = 30 volts
(e)   |VAB| = 40 volts

### QUESTION 22*

This and the following three questions pertain to the following situation.

Capacitors C2 and C3 are

(a)   in parallel.
(b)   in series.
(c)   neither in series nor in parallel.

### QUESTION 23*

Compare V1 the potential across capacitor 1 with V5 the potential across capacitor 5.

(a)   |V1| > |V5|
(b)   |V1| = |V5|
(c)   |V1| < |V5|

### QUESTION 24*

Calculate U, the total energy stored by all of the capacitors in the circuit.

(a)   U = 27 J
(b)   U = 51 J
(c)   U = 94 J
(d)   U = 137 J
(e)   U = 149 J

### QUESTION 25**

Calculate the charge Q1, on the positive plate of capacitor C1.

(a)   Q1 = 29.2 mC
(b)   Q1 = 45.8 mC
(c)   Q1 = 52.4 mC
(d)   Q1 = 61.0 mC
(e)   Q1 = 73.8 mC

### QUESTION 26**

A parallel plate capacitor is connected it to a 5 Volt battery. If a dielectric is inserted between the plates of the capacitor (while it remains connected to the battery), the charge on the capacitor plates will

(a)   increase.
(b)   remain the same.
(c)   decrease.

### QUESTION 27***

This and the following three questions pertain to the following situation.

In the circuit shown, the switch has been open for a long time so that the capacitor is uncharged.

What is the current through the battery immediately after the switch is closed?

(a)   I(0+) = 2V/R
(b)   I(0+) = V/(2R)
(c)   I(0+) = V/R

### QUESTION 28***

Which plot shows the current through the horizontal resistor as a function of time starting just after the switch is closed?

(a)
(b)
(c)

### QUESTION 29**

What is the charge on the capacitor after the switch has been closed for a long time?

(a)   Q(¥) = CV/2
(b)   Q(¥) = CV
(c)   Q(¥) = 2CV

### QUESTION 30***

After being closed for a long time, the switch is opened. How long does it take for the charge on the capacitor to decrease to e-1 [i.e., (2.718)-1] of the charge that it had just before the switch is opened?

(a)   RC/2
(b)   RC
(c)   2RC

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.