Fall 2004 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 ***.

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. The exam period was 90 minutes; the mean score was 100.5; the median was 102. Click here to see the formula sheet that came with the exam.


QUESTION 1*

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

Sphere A is a metal sphere of radius 7 mm with a charge of +5 μC. Sphere B is a metal sphere of radius 7 mm with a charge of -5 μC.

Sphere A and sphere B are placed 1.5 m apart. What is the approximate magnitude of the force between them?

(a)   0 N
(b)   0.10 N
(c)   0.27 N
(d)   0.39 N
(e)   0.44 N


QUESTION 2**

The two spheres are now brought into contact, and then separated again by 1.5 m. What is the magnitude of the force between them now?

(a)   0 N
(b)   0.10 N
(c)   0.27 N
(d)   0.39 N
(e)   0.44 N


QUESTION 3**

If you were to start with sphere A with the same charge of +5 μC, but with sphere B with a charge of -15 μC, then bring them into contact and separate them again by 1.5 m, the magnitude of the force on them would now be

(a)   equal to the magnitude of the force in the previous question.
(b)   different from magnitude of the force in the previous question.


QUESTION 4**

According to one model of the Hydrogen atom, it consists of a proton circled by an electron whose orbit has a radius of R = 5.3 × 10-11 m. The charge of the proton is +1.6 × 10-19 C, and its mass is 1.7 × 10-27 kg. The charge of the electron is -1.6 × 10-19 C, and its mass is 9.1 × 10-31 kg. How fast is the electron moving if the centripetal acceleration (ac = v2/R) is provided by the electric force exerted by the proton?

(a)   v = 300 km/s
(b)   v = 750 km/s
(c)   v = 1310 km/s
(d)   v = 1850 km/s
(e)   v = 2180 km/s


QUESTION 5**

This and the following question are related.

Two charges, one of +12 μC, the other of +3 μC, are 3 cm apart, as shown in the figure.

Where does the total electric field due to these two charges vanish?

(a)   2 cm left of the +12 μC charge
(b)   1 cm left of the +12 μC charge
(c)   1 cm right of the +12 μC charge
(d)   2 cm right of the +12 μC charge
(e)   4 cm right of the +12 μC charge


QUESTION 6*

If you were to replace the +12 μC charge by a -12 μC charge, and the +3 μC charge by a -3 μC charge, your answer to the previous question would be the same.

(T)   True
(F)   False


QUESTION 7*

Which one of the following figures best represents the electric field lines due to two spheres with +10 μC of charge?

(a)   
(b)   
(c)   


QUESTION 8*

The magnitude of the electric field in the region between the two oppositely-charged parallel plates of a capacitor is

(a)   greatest near the positively charged plate.
(b)   uniform throughout the region.
(c)   greatest near the negatively charged plate.


QUESTION 9*

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

(a)   
(b)   


QUESTION 10*

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

Four point charges are arranged in this configuration. Each grid line is 1m.

Calculate the x-component of the electric field at (0,3) due to the four charges shown.

(a)   Ex = 1.23 × 103 N/C
(b)   Ex = 2.62 × 103 N/C
(c)   Ex = 3.46 × 103 N/C
(d)   Ex = 5.43 × 103 N/C
(e)   Ex = 6.78 × 103 N/C


QUESTION 11*

Calculate the y-component of the electric field at (0,3) due to the four charges shown

(a)   Ey = -1.60 × 104 N/C
(b)   Ey = -3.94 × 104 N/C
(c)   Ey = -5.12 × 104 N/C
(d)   Ey = -6.89 × 104 N/C
(e)   Ey = -7.14 × 104 N/C


QUESTION 12*

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

(a)   1.08 × 10-5 N
(b)   2.27 × 10-5 N
(c)   4.73 × 10-5 N
(d)   9.26 × 10-5 N
(e)   1.40 × 10-4 N


QUESTION 13*

Calculate the electric potential at (0, 3) due to the four charges (where the electric potential very far away is zero).

(a)   3.19 × 103 V
(b)   4.04 × 103 V
(c)   7.39 × 103 V
(d)   2.40 × 104 V
(e)   8.18 × 104 V


QUESTION 14**

What is the total potential energy stored in this system of four charges (where the potential energy is zero when the charges are very widely separated)?

(a)   -1.40 × 10-2 J
(b)   -3.15 × 10-2 J
(c)   -5.43 × 10-2 J
(d)   -8.76 × 10-2 J
(e)   -9.80 × 10-2 J


QUESTION 15***

The magnitude of the force on the +6 μC charge is

(a)   greater than the magnitude of the force on the -6 μC charge.
(b)   equal to the magnitude of the force on the -6 μC charge.
(c)   less than the magnitude of the force on the -6 μC charge.


QUESTION 16**

A parallel plate capacitor is connected 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 17*

This and the next question pertain to the following situation:

An isolated parallel-plate capacitor has area A = 2.0 × 10-4 m2 and plate separation d = 3 × 10-5 m. The charge on each plate has magnitude Q = 15 μC. The capacitor is initially filled with air (κ = 1).

Compute the energy stored in the capacitor.

(a)   1.91 J
(b)   3.83 J
(c)   5.24 J
(d)   8.39 J
(e)   9.56 J


QUESTION 18***

Now a dielectric is inserted between the plates (the capacitor remains in isolation from any external circuit). The stored energy will

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


QUESTION 19*

This and the next question pertain to the diagram below:

What is the resistance between point A and B when the switch is open?

(a)   10 kΩ
(b)   20 kΩ
(c)   30 kΩ
(d)   40 kΩ
(e)   50 kΩ


QUESTION 20*

What is the resistance between point A and B when the switch is closed?

(a)   3.33 kΩ
(b)   10.56 kΩ
(c)   14.29 kΩ
(d)   29.12 kΩ
(e)   106.04 kΩ


QUESTION 21**

In lab you used "single throw" switches that switch between two states: open and closed, or connected and disconnected. The circuits below also use "double throw" switches that switch between two different states:

Which circuit shown below is wired so that either switch can turn on the lamp, regardless of the state of the other switch? The correct answer to this question is called "three-way wiring," and is probably used in your apartment or dormitory.

(a)   
(b)   
(c)   


QUESTION 22*

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

The switch in each circuit has been open for a very long time.

Which one of the graphs shown below most accurately describes the behavior of the current through the resistor after the switch in any of the circuits is closed?

(a)   
(b)   
(c)   


QUESTION 23**

In which circuit will the current through the resistor change most slowly after the switch in that circuit is closed?

(a)   
(b)   
(c)   


QUESTION 24*

What is the current through the resistor in circuit A immediately after the switch in circuit A is closed?

(a)   0.11 A
(b)   0.45 A
(c)   0.67 A
(d)   0.99 A
(e)   1.56 A


QUESTION 25**

What is the charge on the 1 μF capacitor in circuit B in the switch in circuit B is closed and left closed for a long time?

(a)   1 μC
(b)   2 μC
(c)   3 μC
(d)   5 μC
(e)   6 μC


QUESTION 26**

A lamp is connected in series with a resistor to a 12 V battery as in the circuit shown below. The lamp is designed to work when the voltage drop across it is 4 V and when it dissipates 12 W.

What should be the resistance of the resistor so that the lamp works as designed?

(a)   0.12 Ω
(b)   0.54 Ω
(c)   2.67 Ω
(d)   5.78 Ω
(e)   98 Ω


QUESTION 27**

A 1 mF capacitor is left on a table at the nuclear power plant after being charged by connecting it to a 1000 V power supply. Homer Simpson, thinking that the capacitor is a donut, quickly grabs the capacitor by holding one terminal in his right hand and the other terminal in his left hand. If the electrical resistance through Homerís body from one hand to the other is 1 MΩ, what is the current through Homer 1 minute after he grabs the capacitor?

(a)   0.13 mA
(b)   0.87 mA
(c)   0.94 mA
(d)   1.24 mA
(e)   5.99 mA


QUESTION 28*

In the circuit shown below, the 5 V battery will overheat and explode if it supplies more than 1 mA. What is the smallest value of the resistor labeled R that will keep the battery from exploding?

(a)   1.0 kΩ
(b)   2.5 kΩ
(c)   3.8 kΩ
(d)   6.5 kΩ
(e)   9.9 kΩ