### Spring 2000 Physics 102 Hour Exam 2(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 120. When the exam was given, the minimum "A" score was 107; the minimum "B" was 92; the minimum "C" was 78; the minimum "D" was 60. The mean was 93.3; the median was 94. Click here to see formula sheet 1, formula sheet 2 that came with the exam.

### QUESTION 1*

Two particles with equal but opposite charge are emitted back-to-back at the same speed from the center of the diagram below. Their trajectories lie in a plane normal to the magnetic field that points into the page. The signs of the particles (positive or negative) are indicated by the "+" or "-" at the ends of the arrows. Which picture at right could be correct?

(a)
(b)
(c)

### QUESTION 2*

The figure to the right illustrates a plane electromagnetic wave. Compare the z-component of the electric field at the points a, b and c.

(a)   Eza = Ezb = Ezc
(b)   Eza = - Ezc ; Ezb = 0
(c)   Eza > Ezb > Ezc

### QUESTION 3*

In the figure are shown two conducting rings, placed close together. In the loop marked left, there is an increasing current in the direction shown by the arrow. In the right ring, a current will

(a)   not flow.
(b)   flow in the same direction as in the left ring.
(c)   flow in the opposite direction as in the left ring.

### QUESTION 4*

There is a solenoid with length L, total number of turns N, and current I. Which procedure maximizes the magnitude of the magnetic field at the center of the solenoid.

(a)   L, N and I are doubled.
(b)   L and I are doubled and N is intact.
(c)   N and I are doubled and L is intact.

### QUESTION 5*

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

The Acme Particle Spectrometer shown here consists of a uniform magnetic field |B| = 0.93 T either into or out of the page, in the region of the shaded box. Particles #1 through #4 all have charge magnitude |q| = 1.6 × 10-19 C. They enter with the same initial velocity v = 2 × 106 m/s and follow the trajectories shown.

Which particle is most massive?

(a)   #1 or #2
(b)   #3
(c)   #4

### QUESTION 6*

The mass of particle #3 is determined to be 3.34 × 10-27 kg. Calculate the distance L labeled on the diagram.

(a)   L = 0.041 m
(b)   L = 0.055 m
(c)   L = 0.060 m
(d)   L = 0.079 m
(e)   L = 0.082 m

### QUESTION 7*

You learn that particle #2 is positively charged. Which way does the magnetic field point?

(a)   into the page
(b)   out of the page

### QUESTION 8*

What is the magnitude of the force on particle #4 when it is at the point marked a (the top of its trajectory)?

(a)   F = 1.06 × 10-13 N
(b)   F = 1.59 × 10-13 N
(c)   F = 2.22 × 10-13 N
(d)   F = 2.98 × 10-13 N
(e)   F = 3.78 × 10-13 N

### QUESTION 9*

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

Two fixed conductors are connected by a resistor of resistance 15 ohms. The two fixed conductors are separated by 3 m. A moving conductor slides on them at velocity 7 m/s. Out of the page is a uniform magnetic field (shown by the black dots in the figure) with a magnitude of 2x10-3T. Points a and b are two points on the circuit just above and below the resistor.

In which direction does the current flow through the resistor?

(a)   from a to b
(b)   from b to a

### QUESTION 10*

What force must be applied to the bar to keep it moving at constant velocity?

(a)   0.39 × 10-5 N
(b)   1.7 × 10-5 N
(c)   5.3 × 10-5 N
(d)   12. × 10-5 N
(e)   53. × 10-5 N

### QUESTION 11*

What is the power being dissipated by the resistor?

(a)   0.118 × 10-3 W
(b)   0.842 × 10-3 W
(c)   3.27 × 10-3 W
(d)   38.7 × 10-3 W
(e)   73.2 × 10-3 W

### QUESTION 12*

If the velocity of the moving bar is doubled, what happens to the power dissipated by the resistor?

(a)   The power increases by a factor of 2.
(b)   The power decreases by a factor of 2.
(c)   The power increases by a factor of 4.
(d)   The power decreases by a factor of 4.
(e)   The power is unchanged.

### QUESTION 13*

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

In this problem all voltages and currents given and asked for are rms values. The values of the frequency of the generator, the capacitance, inductance, and impedance of the circuit are given to the right of the circuit, along with the rms current flowing in the circuit.

What is the resistance R of this circuit?

(a)   R = 125 W
(b)   R = 197 W
(c)   R = 307 W
(d)   R = 428 W
(e)   R = 632 W

### QUESTION 14*

What is the rms voltage of the generator?

(a)   11.6 V
(b)   24.5 V
(c)   49.2 V

### QUESTION 15*

The frequency at which this circuit is operating is

(a)   below the resonant frequency.
(b)   above the resonant frequency.

### QUESTION 16*

Calculate VC, the rms voltage across the capacitor.

(a)   VC = 11.6 V
(b)   VC = 24.5 V
(c)   VC = 39.8 V
(d)   VC = 49.2 V
(e)   VC = 78.6 V

### QUESTION 17*

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

In the figure is shown a rectangular loop of wire shown in edge view. The loop consists of a single turn of wire that is being rotated at a constant frequency in a uniform, horizontal magnetic field as indicated in the figure, where the sense of rotation is shown. Wires a and b, which are perpendicular to the plane of the paper, are indicated by arrows. The loop has a finite resistance, and has an induced current flowing in it.

At the moment shown in the figure, the flux through the loop is

(a)   increasing.
(b)   decreasing.

### QUESTION 18**

At the moment shown in the figure, the sense of the current flowing in the loop is

(a)   out of the page in wire a, into the page in wire b.
(b)   into the page in wire a, out of the page in wire b.

### QUESTION 19**

When the angle between the loop normal and the B-field reaches 90°, the magnitude of the emf in the loop will be

(a)   larger than it is for the loop in the position shown.
(b)   smaller than it is for the loop in the position shown.
(c)   the same as it is for the loop in the position shown.

### QUESTION 20*

When the loop is in the position shown, the force exerted by the magnetic field on wire a is in the

(a)   horizontal direction.
(b)   vertical direction.

### QUESTION 21*

This and the next two questions are about the following situation:

In the figure is shown a square loop carrying a current of 2.5 A in a uniform B field of .02 T. The B-field makes an angle of 45° with the sides of the loop. The length of a loop side is .03 m.

What is |Fab| the magnitude of the magnetic force on side ab?

(a)   |Fab| = 0 N
(b)   |Fab| = 3.6 × 10-4 N
(c)   |Fab| = 10.6 × 10-4 N
(d)   |Fab| = 15.0 × 10-4 N
(e)   |Fab| = 18.4 × 10-4 N

### QUESTION 22*

The direction of the force on side ab is

(a)   out of the page.
(b)   into the page.

### QUESTION 23**

The magnitude of the torque on the loop is

(a)   0 Nm
(b)   3.18 × 10-5 Nm
(c)   4.50 × 10-5 Nm

### QUESTION 24**

This and the next two questions are about the following situation:

The wires are located at (-2,0) meters and (2,0) meters. The former carries 3 A coming out from the sheet of the paper, and the latter 3 A going into it.

What is By, the y component of the magnetic field at the origin?

(a)   By = -6 × 10-7 T
(b)   By = -3 × 10-7 T
(c)   By = 0 T
(d)   By = +3 × 10-7 T
(e)   By = +6 × 10-7 T

### QUESTION 25**

What is the x-component of the force on a 5 meter long segment of wire B due to the magnetic field from wire A?

(a)   F = -2.25 × 10-6 N
(b)   F = -1.25 × 10-6 N
(c)   F = 0 N
(d)   F = +1.25 × 10-6 N
(e)   F = +2.25 × 10-6 N

### QUESTION 26***

Now a third wire C, carrying 3 A coming out of the page is placed at location (-2,2) meters. Which arrow of those shown at the far right best represents the direction of the force on C due to the currents in wires A and B?

(a)
(b)
(c)
(d)
(e)

### QUESTION 27*

This and the next three questions are about the following situation:

A circular conducting loop with resistance of 5 ohms and diameter d=0.4 m surrounds a long solenoid with radius R=0.15 m and 2x104 turns/meter. The current in the solenoid is flowing in the counterclockwise direction producing a uniform magnetic field inside the solenoid of B=0.75 T.

From the end view, the magnetic field at the center of the solenoid is pointing

(a)   into the page.
(b)   out of the page.

### QUESTION 28*

Calculate the magnitude of the current Is flowing in the solenoid.

(a)   Is = 9.5 A
(b)   Is = 16.4 A
(c)   Is = 29.8 A
(d)   Is = 58.7 A
(e)   Is = 68.2 A

### QUESTION 29***

The current in the solenoid is steadily decreased to zero over a period of 5 seconds.

Calculate IL the magnitude of the average induced current in the outside loop while the current in the solenoid is being decreased.

(a)   IL = 2.12 × 10-3 A
(b)   IL = 2.46 × 10-3 A
(c)   IL = 3.18 × 10-3 A
(d)   IL = 3.76 × 10-3 A
(e)   IL = 4.30 × 10-3 A

### QUESTION 30***

From the end view, which direction will the induced current in the outer loop flow?

(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.