### Fall 2001 Physics 102 Hour Exam 2(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 130. When the exam was given, the mean was 96.7; the median was 100. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

This and the next question are about the following situation:

Three particles of the same charge and the same speed of v, but with three different masses, enter a region of constant magnetic field into the page (B = 0.5 T)

Which particle has the largest mass?

(a)   particle #1
(b)   particle #2
(c)   particle #3

### QUESTION 2***

A uniform electric field is now applied in the region of the magnetic field so that particles continue to move up vertically without bending. What should be the direction of this electric field?

(a)   right
(b)   left
(c)   up
(d)   down
(e)   into the page

### QUESTION 3**

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

In region A, there exists a constant magnetic field (B = 2 T) pointing into the page. In region B, a constant magnetic field of unknown direction and magnitude exists. A charged particle of mass 3*10-20 Kg moves in an orbit in the plane of the paper as indicated by the arrowed curve. Since the magnetic field does not do any work, the particle’s speed remains constant and its speed is given by 103 m/sec.

What is the direction of the magnetic field in region B?

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

### QUESTION 4*

Which one of the following statements is true?

(a)   The magnetic field is stronger in region A than in region B.
(b)   The magnetic field is stronger in region B than in region A.
(c)   The magnetic field has the same magnitude in region A and B.

### QUESTION 5*

If the magnitude of the charge is 2.4 × 10-15 C, how much time would the particle spend in region A each time it enters the region A until it exits into region B?

(a)   1.2 × 10-4 seconds
(b)   9.1 × 10-5 seconds
(c)   5.5 × 10-5 seconds
(d)   2.0 × 10-5 seconds
(e)   1.1 × 10-5 seconds

### QUESTION 6*

There is a wire carrying current out of the paper as shown by a thick circle with a dot in the middle. Concentric circles with arrows outside the wire represent the magnetic field lines. Which one of these diagrams describes the magnetic field lines the best?

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

### QUESTION 7**

The magnetic fields B1 = 1.2 × 10-4 Tesla and B2 = 0.7 × 10-4 Tesla are measured in the laboratory at two distances d1= 1 cm and d2 = 2 cm from a long, straight wire that carries current . The current is perpendicular to the paper in the figure below and the magnetic fields are in the plane of the paper. A constant background magnetic field may also be present due to the earth, magnets on the laboratory table, etc. What is the magnitude of the current carried by the wire?

(a)   0.80 amp
(b)   1.6 amp
(c)   4.7 amp
(d)   5.0 amp
(e)   8.2 amp

### QUESTION 8**

This and the next question are about the following situation:

Three parallel wires carry identical currents (I1 = I2 = I3 = 3 A) in the same direction as shown.

What is the magnitude of the magnetic field at point x (1 meter away from wire #1 toward the other two wires)?

(a)   9.2 × 10-7 T
(b)   7.5 × 10-7 T
(c)   6.3 × 10-7 T
(d)   4.5 × 10-7 T
(e)   3.0 × 10-7 T

### QUESTION 9**

What is the direction of the total force on wire #3 due to wire #1 and wire #2 ?

(a)   up
(b)   down
(c)   into the paper
(d)   out of the paper
(e)   right

### QUESTION 10*

This and the next question are about the following situation:

A square loop (0.5 meter sides) is placed in a constant magnetic field (B=5 T) as shown. An unknown current is flowing into and out of the paper as indicated by the x and the dot.

Due to the magnetic forces acting on the wire segments, a net torque will be generated. In which direction would the torque rotate the loop?

(a)   clockwise
(b)   counter-clockwise

### QUESTION 11*

The magnitude of the torque is 0.1 N*m. What is the magnitude of the current?

(a)   0.06 A
(b)   0.16 A
(c)   0.25 A
(d)   0.37 A
(e)   0.52 A

### QUESTION 12**

A circular conducting loop is being moved upward (toward the current-carrying wire) at a constant speed v. What will be the direction of the induced current?

(a)   No current will be induced (no flux change).
(b)   Current will be induced clockwise.
(c)   Current will be induced counter-clockwise.

### QUESTION 13***

A bar magnetic with constant velocity passes through the inside of a solenoid as indicated in the figure. The ammeter A measures any current that is induced in the wire of the solenoid. This current is positive if it is in the same direction as the arrow below the ammeter. As the magnet passes through the solenoid, the induced current is

(a)   zero.
(b)   always positive.
(c)   always negative.
(d)   first positive and then negative.
(e)   first negative and then positive.

### QUESTION 14*

A square, conducting loop of side length 1 cm is enclosed by a long solenoid with a larger diameter as shown. The solenoid is composed of a wire with 100 turns per cm and the current in the wire flows in the clockwise direction as shown. If the flux through the loop is 4*10-5 Weber, what is the current strength?

(a)   20.7 A
(b)   31.8 A
(c)   40.1 A

### QUESTION 15*

A square loop is enclosed by a long solenoid with a current flowing as shown by the arrow. Which configuration will give the largest magnetic flux?

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

### QUESTION 16*

This and the next question are about the following situation:

A generator consists of a single square loop being rotated in a uniform magnetic field B = 0.25 tesla. The generator produces the following output V = 15 sin (38 t) volts. The picture shows the orientation of the loop at time t = 0.

Calculate the length L of a side of the rotating loop.

(a)   L = 1.26 m
(b)   L = 1.75 m
(c)   L = 2.03 m

### QUESTION 17***

Which is a possible direction for the external magnetic field?

(a)   to the left
(b)   up
(c)   in to the page

### QUESTION 18**

A 10 volt AC voltage source is connected to a transformer with 2 primary coils and 4 secondary coils. The output of the first transformer is connected to the input of another transformer with 8 primary coils and 16 secondary coils as shown below. What is the voltage across the secondary of the second transformer?

(a)   2.5 volts
(b)   5.0 volts
(c)   20 volts
(d)   40 volts
(e)   80 volts

### QUESTION 19*

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

Unpolarized light is incident on a series of two linear polarizers with transmission axis aligned 40° and 70° with respect to the vertical.

If the incident intensity is I0, what is the intensity I2 transmitted by the stack?

(a)   I2 = 0
(b)   I2 = cos2(40°) cos2(70°)
(c)   I2 = cos2(40°) cos2(30°)
(d)   I2 = ˝ cos2(40°)
(e)   I2 = ˝ cos2(30°)

### QUESTION 20**

If a third polarizer is placed in front of the first one, the transmitted intensity can

(a)   never increase.
(b)   never decrease.
(c)   increase or decrease depending on the orientation of its transmission axis.

### QUESTION 21*

If a third polarizer is placed between the two polarizers shown above, the transmitted intensity can

(a)   never increase.
(b)   never decrease.
(c)   increase or decrease depending on the orientation of its transmission axis.

### QUESTION 22*

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

The RLC circuit below is being driven by an AC source resulting in a maximum current Imax = 0.25 amps.

Calculate VL the maximum voltage across the inductor.

(a)   VL = 7 volts
(b)   VL = 18 volts
(c)   VL = 22 volts
(d)   VL = 25 volts
(e)   VL = 34 volts

### QUESTION 23*

Calculate V0 the maximum voltage across the generator.

(a)   V0 = 12.5 volts
(b)   V0 = 13.9 volts
(c)   V0 = 15.3 volts
(d)   V0 = 18.4 volts
(e)   V0 = 21.8 volts

### QUESTION 24*

What is the average power provided by the AC source in the circuit?

(a)   0
(b)   0.3 J/s
(c)   1.6 J/s
(d)   4.8 J/s
(e)   8.3 J/s

### QUESTION 25***

What is the relationship between the time at which the maximum occurs for the current I in the circuit and the time at which the maximum occurs for the voltage E(t) across the AC source?

(a)   I reaches its maximum before E(t) reaches its maximum.
(b)   I reaches its maximum after E(t) reaches its maximum.
(c)   I reaches its maximum at the same time that E(t) reaches its maximum.

### QUESTION 26*

The figure to the right illustrates a plane electromagnetic wave. Compare the magnitudes of the x-component of the magnetic field at the points a and b.

(a)   Ba > Bb
(b)   Ba = Bb
(c)   Ba < Bb

### QUESTION 27*

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

A local radio station broadcasts at the frequency 107.1 MHz (107.1 × 106 Hz). At Loomis lab, the average energy density of this signal is 4 × 10-12 J/m3.

What i s the wavelength l of this signal?

(a)   l = 1.5 m
(b)   l = 2.3 m
(c)   l = 2.8 m

### QUESTION 28**

How much energy does a 3m2 flat surface receive from this signal in 5 seconds?

(a)   3.6 mJ
(b)   6.0 mJ
(c)   18 mJ

### QUESTION 29*

If the tuner of your radio involves an RLC circuit with an inductance L = 2 × 10-6 H, to obtain what capacitance C should you adjust the knob on your radio to hear this radio station?

(a)   6.3 × 10-13 F
(b)   1.1 × 10-12 F
(c)   7.5 × 10-12 F
(d)   4.4 × 10-11 F
(e)   8.5 × 10-11 F

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.