### Fall 2002 Physics 102 Hour Exam 1(29 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 29 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 102. When the exam was given, the mean was 66.1; the median was 67. Click here to see the formula sheet that came with the exam.

### QUESTION 1**

This and the next question pertain to the following situation.

A positive point charge Q is located at the origin. A thin, circular, conducting disk is placed at x = 3 m, with its circular faces perpendicular to and centered about the x-axis as shown below. The conducting disk is grounded.

What is the net electric force on the disk due to the point charge?

(a)   toward the point charge Q
(b)   zero
(c)   away from the point charge Q

### QUESTION 2***

Compare |EL|, the magnitude of the electric field 1 meter to the left of the point charge, with |ER|, the magnitude of the electric field 1 meter to the right of the point charge.

(a)   |EL| < |ER|
(b)   |EL| = |ER|
(c)   |EL| > |ER|

### QUESTION 3**

Which figure most closely represents the equipotential lines corresponding to two equal negative point charges?

(a)
(b)
(c)

### QUESTION 4*

This and the next four questions pertain to the following situation.

Two charges are placed at (-3, 0) and (0, 0) as shown. The grid spacing is in meters.

What is the magnitude of the electric force on the 3 mC charge due to the -2 mC charge?

(a)   1.80 × 10-2 N
(b)   5.99 × 10-3 N
(c)   9.99 × 10-4 N

### QUESTION 5**

There is a point on the x-axis where the electric field is exactly zero. In which region is this point located?

(a)   x > 0
(b)   x < -3 m
(c)   between x = -3 m and x = 0

### QUESTION 6**

Calculate the y-component of the electric field at (0, 2).

(a)   -5.65 × 103 V/m
(b)   -3.34 × 103 V/m
(c)   0
(d)   +3.34 × 103 V/m
(e)   +5.65× 103 V/m

### QUESTION 7*

Calculate the electric potential at (0, 2).

(a)   7.48 × 103 V
(b)   1.73 × 103 V
(c)   -1.51 × 103 V

### QUESTION 8***

Calculate the work required to move a +1 mC charge along the y axis from (0,2) to (0,3).

(a)   -2.65 × 10-3 J
(b)   -1.87 × 10-3 J
(c)   0
(d)   +1.87 × 10-3 J
(e)   +2.65 × 10-3 J

### QUESTION 9*

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

A region in space contains a uniform electric field of Ex = 0 and Ey = 2 V/m and no gravitational field. A particle of mass M = 0.0015 kg and charge Q = -0.005 C is at the origin (0, 0) at time t = 0, moving to the right (+x direction) with a speed of 2 m/s.

Find the x position of the particle at time t = 4 s.

(a)   x = 2 m
(b)   x = 8 m
(c)   x = 16 m

### QUESTION 10**

Find the y position of the particle at time t = 4 s.

(a)   y = -53.3 m
(b)   y = -26.6 m
(c)   y = -13.3 m

### QUESTION 11***

Calculate the kinetic energy of the particle when it reaches a point with y = -0.5 m.

(a)   8.00 × 10-3 J
(b)   13.3 × 10-3 J
(c)   26.0 × 10-3 J

### QUESTION 12**

As the particle travels through the field, its electric potential energy

(a)   increases.
(b)   remains the same.
(c)   decreases.

### QUESTION 13*

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

Two capacitors of C1 = 30 µF and C2 = 60 µF are connected by a switch to a battery as shown in the figure. The switch is closed, and capacitor C1 acquires a charge Q1= 1.5 × 10-3 C. The switch is then opened again (as shown).

Calculate the energy stored in capacitor C1.

(a)   1.5 × 10-3 J
(b)   3.75 × 10-2 J
(c)   7.5 × 10-2 J

### QUESTION 14*

Calculate the voltage across C2.

(a)   25 V
(b)   50 V
(c)   75 V

### QUESTION 15*

What is the equivalent capacitance of the pair of capacitors?

(a)   20 µF
(b)   45 µF
(c)   90 µF

### QUESTION 16***

A material of relative dielectric constant k = 1.5 is now inserted into the charged capacitor C1. As the dielectric is inserted into capacitor C1 the charge on capacitor C1

(a)   increases.
(b)   remains the same.
(c)   decreases.

### QUESTION 17*

This and the next question pertain to the following situation.

A battery with e = 20 V is used to charge a capacitor with capacitance C = 5 µF through a resistor R, as shown in the circuit diagram. The voltage across the resistor R is measured as a function of time after the switch is closed and the resulting empirical data is shown below:

How much charge is on the capacitor after a very long time?

(a)   10-4 C
(b)   10-3 C
(c)   10-2 C

### QUESTION 18***

Using the data on the graph above, estimate the value of the resistance R.

(a)   5 W
(b)   20 W
(c)   40 W

### QUESTION 19*

This and the next four questions pertain to the following situation.

For the first two problems, consider the circuit above with the switch S open, as shown.

Calculate the equivalent resistance of the circuit.

(a)   2.00 W
(b)   2.08 W
(c)   2.40 W

Calculate I4.

(a)   2.0 A
(b)   2.5 A
(c)   3.0 A

### QUESTION 21*

For this and the following two questions, consider the circuit above with the switch S closed.

Calculate the equivalent resistance of the circuit.

(a)   2.00 W
(b)   2.08 W
(c)   2.40 W

### QUESTION 22**

What is the electric potential difference between the switch and the negative side of the battery at point b?

(a)   6 V
(b)   9 V
(c)   15 V

### QUESTION 23***

Calculate IS. (A positive number indicates current is going in direction shown by arrow in figure.)

(a)   -3.0 A
(b)   -0.75 A
(c)   0 A
(d)   0.75 A
(e)   3.0 A

### QUESTION 24**

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

In the circuit to the right, the switch has been open for a long time as shown.

Calculate IB, the current through the battery, immediately after the switch is closed.

(a)   IB = 0.33 A
(b)   IB = 0.5 A
(c)   IB = 1 A

### QUESTION 25*

Calculate IB, the current through the battery, after the switch has been closed for a long time.

(a)   IB = 0.33 A
(b)   IB = 0.5 A
(c)   IB = 1 A

### QUESTION 26***

After the switch has been closed for a long time, the charge on the capacitor is observed to be 15 mC. What is the capacitance C?

(a)   C = 2.25 × 10-3 F
(b)   C = 1.50 × 10-3 F
(c)   C = 0.75 × 10-3 F

### QUESTION 27*

This and the next question pertain to the following situation.

Eleven positive point charges +Q and one negative charge –Q are situated on the perimeter of a circle with radius r, as shown in the figure.

Calculate the magnitude of the electric field at the center of the circle.

(a)   |E| = 0
(b)   |E| = 1 k Q / r2
(c)   |E| = 2 k Q / r2
(d)   |E| = 10 k Q / r2
(e)   |E| = 11 k Q / r2

### QUESTION 28*

Calculate the electric potential at the center of the circle.

(a)   V = 0
(b)   V = 1 k Q / r
(c)   V = 2 k Q / r
(d)   V = 10 k Q / r
(e)   V = 11 k Q / r

### QUESTION 29*

A set of batteries and resistors is connected as shown below.

Which one of the following equations is correct?

(a)   e1 + I1 R1 - e2 + I1 R2 = 0
(b)   I1 – I2 = I3
(c)   -e1 + I1 ( R1 + R2) + I3 R3 = 0

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.