### Spring 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 98. When the exam was given, the mean was 63.0; the median was 65. Click here to see the formula sheet that came with the exam.

### QUESTION 1*

A positive point charge q is placed midway between an uncharged conductor and an uncharged insulator as shown below.

What is the net electric force on q ?

(a)   toward the conductor
(b)   toward the insulator
(c)   zero

### QUESTION 2*

This and the following question pertain to the following situation.

The drawing shows two charges q1 and q2 fixed to a circle. At the center of the circle they produce a net electric field that is directed along the vertical axis.

The charges q1 and q2 must have the same sign.

(T)   True
(F)   False

### QUESTION 3**

Compare the magnitudes of q1 and q2.

(a)   |q1| > |q2|
(b)   |q1| = |q2|
(c)   |q1| < |q2|

### QUESTION 4**

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

A uniform electric field E = 35 N/C is directed upward as shown in the figure. Consider Wac the work YOU would do to move a positive charge from point a to point c.

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

### QUESTION 5**

Compare the magnitude of the above work, |Wac| with |Wbc|, the magnitude of the work YOU must do to move the same charge from point b to point c.

(a)   |Wac| < |Wbc|
(b)   |Wac| = |Wbc|
(c)   |Wac| > |Wbc|

### QUESTION 6**

Calculate Vac the magnitude of the potential difference between points a and c if all three points lie on an equilateral triangle with hypotenuse dac = 1.41 m, and sides of length 1 meter.

(a)   Vac = 0
(b)   Vac = 35 volts
(c)   Vac = 50 volts

### QUESTION 7*

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

A point charge, Q = +9 nC, is placed at the center of a hollow conductor that is electrically neutral.

Determine the magnitude of the electric field at point A given that the distance between the point charge Q and point A is dA = 5 cm.

(a)   EA = 0
(b)   EA = 8.1 ´103 N/C
(c)   EA = 32 ´103 N/C

### QUESTION 8**

Determine the magnitude of the electric field at point B (inside the conductor) given that its distance from the point charge Q is dB = 10 cm.

(a)   EB = 0
(b)   EB = 8.1 ´103 N/C
(c)   EB = 32 ´103 N/C

### QUESTION 9**

Which of the following pictures best describes the electric field lines for this system?

(a)
(b)
(c)

### QUESTION 10**

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

Two small spheres, A and B, are on a wedge, where L = 2 m. Sphere A is held fixed at the top of the wedge, while sphere B is fixed at a distance d1 = 50 cm from A. The two spheres have charges, QA = -3 µC and QB = +3 µC.

There is a point along the ramp between points A and B where the electric field due to these two charges is zero.

(T)   True
(F)   False

### QUESTION 11**

There is a point along the ramp between points A and B where the electric potential due to these two charges is zero.

(T)   True
(F)   False

### QUESTION 12**

If sphere B has a mass m = 3.3 × 10-2 kg, and is now set free to move on the ramp, which direction will it roll? (Remember g = 9.8 m/s2.)

(a)   Sphere B will not move.
(b)   Sphere B will roll down, away from A.
(c)   Sphere B will roll up, towards A.

### QUESTION 13**

This and the following question pertain to the following situation.

Consider a regular cube with sides of length d = 1 m and positive point charge +Q in all corners except for one which has a negative point charge -Q. The distance from any corner to the center of the cube is r = 0.866 m.

What is the magnitude of electric field at the center of the cube?

(a)   |E| = 0
(b)   |E| = 1 k Q / r2
(c)   |E| = 2 k Q / r2
(d)   |E| = 6 k Q / r2
(e)   |E| = 7 k Q / r2

### QUESTION 14**

What is the electric potential V at the center of the cube?

(a)   V = 0
(b)   V = 1 k Q / r
(c)   V = 2 k Q / r
(d)   V = 6 k Q / r
(e)   V = 7 k Q / r

### QUESTION 15**

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

How much work would YOU have to do to assemble these point charges from far away, to the distribution shown here?

(a)   W = -15 ´ 10-8 J
(b)   W = -9 ´ 10-8 J
(c)   W = 0
(d)   W = 9 ´ 10-8 J
(e)   W = 15 ´ 10-8 J

### QUESTION 16*

What is the electric potential at the origin? (Let the potential at infinity to be 0.)

(a)   49 V
(b)   3.8 V
(c)   0 V
(d)   -3.8 V
(e)   -49 V

### QUESTION 17*

Which arrow best represents the direction of the net electric field at the origin?

(a)
(b)
(c)

### QUESTION 18*

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

Three capacitors (C1 = C2 = 6 µF, C3 = 3µF), two resistors (R1 = 10 W , R2 = 20 W), and a battery (V = 9 volts) are connected as shown. Initially, the switch is open.

At t = 0, the switch is closed. What is the magnitude of I1 the current flowing through the resistor R1 just after the switch is closed?

(a)   I1 = 1.15 A
(b)   I1 = 0.90 A
(c)   I1 = 0.30 A

### QUESTION 19**

Which of the following graphs best represent the current through resistor R1 starting just after the switch is closed?

(a)
(b)
(c)

### QUESTION 20**

How much charge, Q2, is on the capacitor C2 after the switch has been closed for a long time?

(a)   Q2 = 27 µC
(b)   Q2 = 54 µC
(c)   Q2 = 81 µC

### QUESTION 21***

How long after the switch is closed will Q3, the charge on capacitor 3, reach (1-1/e) of its maximum value?

(a)   t = 30 µs
(b)   t = 60 µs
(c)   t = 120 µs

### QUESTION 22***

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

For this circuit, which one of the following equations is not valid?

(a)   +E1 + R1I1 + I2R2 - E2 = 0
(b)   +E1 + (R1/2)I1 - R3I3 + E3 = 0
(c)   +E2 - R2I2 - R3I3 + E3 = 0

### QUESTION 23*

Which one of the following is a valid Kirchhoff current equation for the above circuit?

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

### QUESTION 24***

Let E1 = 9 volts, E2 = 3 volts and E3 = 5 volts. Which of the three points (a, b or c) has the lowest electric potential?

(a)   point a
(b)   point b
(c)   point c

### QUESTION 25**

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

Six resistors shown all have the same resistance of 10 W.

Compare I2, the current through R2, with I5, the current through R5.

(a)   I2 > I5
(b)   I2 = I5
(c)   I2 < I5

### QUESTION 26**

Compare V5, the voltage across R5, with V6, the voltage across R6.

(a)   V5 > V6
(b)   V5 = V6
(c)   V5 < V6

### QUESTION 27**

If the current through R1 is 0.25 A, what is the total power delivered by the battery?

(a)   0.32 W
(b)   1.81 W
(c)   2.9 W
(d)   4.6 W
(e)   7.3 W

### QUESTION 28**

Two identical capacitors C1 and C2 are connect to a battery as shown in the figure. A metal slab is inserted between the plates of C2. With the plate in place, compare Q1 the charge on C1 with Q2 the charge on C2.

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

### QUESTION 29**

Two types of resistors are made of the same material. Type 1 resistor has twice the diameter of Type 2 resistor, but is half as long as the Type 2 resistor. Which of the configurations shown has the higher net resistance?

(a)
(b)

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.