Fall 2003 Physics 102 Hour Exam 1
(28 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 28 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 116. When the exam was given, the mean was 96.8; the median was 101. 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 solid spherical conductor contains no net charge. A point positive charge Q is brought near the conductor. Which of (A) or (B) more correctly describes the resulting charge distribution on the conducting sphere?

(a)   
(b)   


QUESTION 2**

What electric force does the sphere exert on the point charge Q?

(a)   zero force
(b)   a force toward the sphere
(c)   a force away from the sphere


QUESTION 3*

Three charges Q1, Q2 , and Q3 are placed at the corners of an equilateral triangle. If all three charges have the same magnitude and sign, which diagram gives a better representation of the electric field lines near the charges?

(a)   
(b)   


QUESTION 4*

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

A charge of -3 μC is placed at (0, 2) and an equal, but opposite in sign, charge of +3 μC is placed at (0, -2) as shown. The grid spacing is in meters.

What is the direction of the electric field at point A?

(a)   +y direction
(b)   -y direction
(c)   The electric field at point A is zero.


QUESTION 5*

The electric potential vanishes everywhere along the

(a)   x axis
(b)   y axis


QUESTION 6*

What is the electric potential at point B = (4, 2)?

(a)   -4.22 × 102 V
(b)   -6.54 × 102 V
(c)   -1.98 × 103 V
(d)   -2.38 × 103 V
(e)   -9.81 × 103 V


QUESTION 7*

What is the x-component of the electric field at point B?

(a)   -3.98 × 102 V/m
(b)   -6.15 × 102 V/m
(c)   -8.66 × 102 V/m
(d)   -1.09 × 103 V/m
(e)   -2.68 × 103 V/m


QUESTION 8*

What is the y-component of the electric field at point B?

(a)   4.38 × 102 V/m
(b)   5.97 × 102 V/m
(c)   9.13 × 102 V/m
(d)   3.27 × 103 V/m
(e)   7.65 × 103 V/m


QUESTION 9**

The work that it takes to move a +1 μC charge from point B to point A is

(a)   positive.
(b)   negative.
(c)   zero.


QUESTION 10**

This and the next question pertain to the following situation.

A uniform electric field points in the negative x direction as shown in the figure. The magnitude of the electric field is 2.6 V/m. How much work will it take to move a particle of charge of +2 μC from the point x = 0, y = 0 to the point x = 3 m, y = 4 m?

(a)   1.56 × 10-5 J
(b)   2.08 × 10-5 J
(c)   2.60 × 10-5 J


QUESTION 11*

If after being moved to x = 3 m, y = 4 m, the charged particle is released, it will

(a)   move directly to the right.
(b)   move directly to the left.
(c)   move directly to the origin.


QUESTION 12***

At top right is shown a plot of electric potential V vs. x. Below it are three possible plots of the corresponding x-component of the electric field E vs. x. Which of A, B, or C represents the correct electric field?

(a)   
(b)   
(c)   


QUESTION 13*

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

Three capacitors are connected to a battery as shown below.

Compare V3 (the voltage across capacitor C3) with V2 (the voltage across capacitor C2).

(a)   V3 > V2
(b)   V3 = V2
(c)   V3 < V2


QUESTION 14*

Compare Q3 (the charge on capacitor C3) with Q2 (the charge on capacitor C2).

(a)   Q3 > Q2
(b)   Q3 = Q2
(c)   Q3 < Q2


QUESTION 15*

Compare Q1 (the charge on capacitor C1) with Q2 + Q3.

(a)   Q1 > Q2 + Q3
(b)   Q1 = Q2 + Q3
(c)   Q1 < Q2 + Q3


QUESTION 16*

Calculate Ceq, the equivalent capacitance of the three capacitors in the circuit.

(a)   Ceq = 12.1 mF
(b)   Ceq = 18.4 mF
(c)   Ceq = 21.2 mF
(d)   Ceq = 28.5 mF
(e)   Ceq = 33.3 mF


QUESTION 17*

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

In the circuit shown below, the battery voltage is 9 V, the resistor R1= 20 Ω, and the capacitor C = 1 μF. The capacitor is initially charged with the polarity shown in the picture and with a voltage of 18 V. Switches S1 and S2 are initially open.

What is the initial charge on the capacitor?

(a)   11 C
(b)   1.8 × 10-5 C
(c)   3.2 × 10-3 C
(d)   1.5 × 10-5 C
(e)   4.1 × 10-9 C


QUESTION 18*

Switch S2 is suddenly closed. What is the current through the 20 Ω resistor immediately afterward?

(a)   0.2 A
(b)   0.9 A
(c)   1.0 A
(d)   0.5 A
(e)   0.3 A


QUESTION 19*

When will the current through the 20 Ω resistor reach 1/e of its initial value?

(a)   2.0 × 10-5 s
(b)   1.0 s
(c)   3.2 × 10-6 s
(d)   5.4 × 10-9 s
(e)   10 s


QUESTION 20*

Once the current through the 20 Ω resistor reaches 1/e of its initial value, switch S1 is suddenly closed (switch S2 remains closed). What is the current through the 20 Ω resistor a long time later?

(a)   2.0 A
(b)   0.23 A
(c)   0.45 A
(d)   20 A
(e)   0.15 A


QUESTION 21*

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

In the circuit shown below, the battery voltage is ε, the resistors R1 = R3 = R and R2 = R4 = 2R.

What is the equivalent resistance for this configuration of resistors?

(a)   5R
(b)   R/10
(c)   3R/2
(d)   6R/5
(e)   R


QUESTION 22*

What is the total power dissipated by resistors R3 and R4?

(a)   ε2/10R
(b)   ε2/R
(c)   ε2/5R
(d)   ε2/20R
(e)   ε2/3R


QUESTION 23*

The battery voltage ε is 9 V and the current through the battery is 2 A. What is R?

(a)   3 Ω
(b)   1 Ω
(c)   10 Ω
(d)   2 Ω
(e)   0.1 Ω


QUESTION 24*

Which of the following choices is correct regarding the potential difference VAB = VA - VB between point A and point B?

(a)   VAB > 0
(b)   VAB < 0
(c)   VAB = 0


QUESTION 25*

This and the next question pertain to the following situation.

Two parallel plate capacitors are constructed as shown. The C1 has plates with dimension W and L separated by a distance d. C2 has plates with dimension 2W and 2L separated by a distance 4d.

Compare the capacitance of the two capacitors.

(a)   C1 > C2
(b)   C1 = C2
(c)   C1 < C2


QUESTION 26**

The two uncharged capacitors are now connected to a battery as shown schematically to the right. Compare |E1| (the magnitude of the electric field between the plates of capacitor C1) with |E2| (the magnitude of the electric field between the plates of capacitor C2).

(a)   |E1| > |E2|
(b)   |E1| = |E2|
(c)   |E1| < |E2|


QUESTION 27**

This and the next question pertain to the following situation.

In the circuit shown below, the resistors all have resistance R. The battery on the left has voltage V, and the battery on the right has voltage 2V.

What is the potential difference VBA = VB - VA between points B and A when the switch is open?

(a)   5V
(b)   V/5
(c)   V/3
(d)   V/6
(e)   3V


QUESTION 28*

Note currents I1 and I2 flowing out of the batteries in the diagram. Which equation is a correct Kirchoff’s voltage law for the loop pictured on the left of the diagram when the switch is closed?

(a)   (I1+I2) R + 2 I1 R = V
(b)   2(I1+I2) R + 3 I1 R = -V