### Spring 2004 Physics 102 Hour Exam 2(27 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 27 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 107. When the exam was given, the mean was 85.4; the median was 87. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

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

A chamber is filled with a uniform magnetic field B with direction as shown (into the paper). Three particles X, Y and Z are produced near the center of the region. Parts of their tracks through the chamber are shown in the figure. The tracks lie in the plane of the paper

The charge carried by particle X is

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

### QUESTION 2*

The charge carried by particle Z is

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

### QUESTION 3*

Particle X has a smaller mass than Particle Y and their charges are related by |qX| = |qY|. Which of the following is a true statement about their speeds?

(a)   |vX| > |vY|
(b)   |vX| = |vY|
(c)   |vX| < |vY|

### QUESTION 4*

Which of the following can be deduced about particle Z?

(a)   Z has a smaller mass than either X or Y.
(b)   Z is moving faster than either X or Y.
(c)   Neither of the above – there is insufficient information.

### QUESTION 5***

You can think of the circling charges X and Y as loops of current. These currents produce their own magnetic fields. Do these add to, or subtract from the external field B?

(a)   The fields due to X and Y are in opposite directions so there is no clear answer.
(b)   Both the fields due to X and Y subtract from the external magnetic field.
(c)   Both the fields due to X and Y add to the external magnetic field.

### QUESTION 6*

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

A single loop of conducting wire of radius 15 cm is immersed in a uniform magnetic field of 0.3 tesla. The direction of this field is parallel to the axis of the loop. The field is turned off in 1.5 s (that is, it goes from full strength to zero tesla in 1.5 s). .

What is the magnitude of the average induced emf during the time the field is being turned off?

(a)   1.4 × 10-2 V
(b)   1.9 × 10-2 V
(c)   0.20 V
(d)   0.35 V
(e)   5.0 V

### QUESTION 7**

As viewed from the position A, the current induced in the loop during this time flows

(a)   clockwise.
(b)   counterclockwise.

### QUESTION 8*

If the loop had been placed in the magnetic field such that the axis were perpendicular to the magnetic field, how would the induced emf in this case (X) compare to that induced in the situation described in the previous two questions, case (Y)?

(a)   X more than Y
(b)   X the same as Y
(c)   X less than Y

### QUESTION 9*

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

For a public performance of a tight-rope walker, two parallel cables are stretched between two high platforms. The figure shows the two cables in perspective as seen from one of the platforms. The performer is to traverse the distance on cable 1. However, a gust of wind makes her fall, in the direction of cable 2. The distance between the cables is r = 3 meters for their full length so, when she falls, the hands of the walker would narrowly miss cable 2. However, you happen to carry a very powerful 12 V battery with you, giving you a chance to rescue the performer.

An attractive force between the wires is required to move cable 2 in the direction of the falling walker. Which way do you connect the plus (+) and minus (–) terminals of your battery to the ends of the wires in the cables?

(a)   + to A, C; – to B, D
(b)   + to A, D; – to B, C
(c)   + to B, D; – to A, C

### QUESTION 10**

For each meter of wire 2 a force of 10N is needed to move the wires enough. What is the amount of current needed in each of the two wires to produce this force?

(a)   9 × 10-4 A
(b)   0.01 A
(c)   6 A
(d)   358 A
(e)   12247 A

### QUESTION 11*

Can you save the performer? The internal resistance of your battery is 0.01 Ohms. What is the maximum total amount of current you can draw from it? (Assume the wires in the cables carry current without resistance).

(a)   0.12 A
(b)   1200 A
(c)   14400 A

### QUESTION 12**

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

The phasor diagram to the right yields information on a particular series RLC circuit. It is only partially labeled, but you should know from examining it the proper quantity that is referred to by each number, given in ohms, in the drawing.

At the instant shown, the generator voltage is zero.

(T)   True
(F)   False

### QUESTION 13*

The element with the greatest maximum voltage is the

(a)   inductor.
(b)   resistor.
(c)   capacitor.

### QUESTION 14*

What is the total impedance, Z, of the circuit?

(a)   Z = 24 Ω
(b)   Z = 36 Ω
(c)   Z = 42 Ω
(d)   Z = 56 Ω
(e)   Z = 68 Ω

### QUESTION 15*

If the inductance L = 0.06 H, what is the frequency of the circuit?

(a)   f = 22 Hz
(b)   f = 49 Hz
(c)   f = 81 Hz
(d)   f = 106 Hz
(e)   f = 159 Hz

### QUESTION 16*

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

In an RLC circuit, the current is always in phase with

(a)   the resistor voltage.
(b)   the inductor voltage.
(c)   the capacitor voltage.

### QUESTION 17*

What is the phase angle Φ for the circuit above?

(a)   Φ = +78.2°
(b)   Φ = +59.5°
(c)   Φ = -26.2°
(d)   Φ = -39.8°
(e)   Φ = -62.4°

### QUESTION 18*

What is the maximum current in the circuit?

(a)   Imax = 0.317 A
(b)   Imax = 0.724 A
(c)   Imax = 1.65 A
(d)   Imax = 2.12 A
(e)   Imax = 2.97 A

### QUESTION 19*

To bring the circuit closer to resonance, the frequency of the oscillating voltage supply should be

(a)   increased.
(b)   decreased.

### QUESTION 20*

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

An unpolarized electromagnetic wave is incident at a series of three linear polarizers, each with the polarization angle rotated at 45° with respect to the previous one.

If the initial intensity of the unpolarized light is I0, what is the intensity I1 transmitted through the first polarizer?

(a)   I1 = I0
(b)   I1 = I0 / 2
(c)   I1 = I0 / 4

### QUESTION 21*

After the first polarizer, the light is linearly-polarized. When it passes through the second polarizer,

(a)   only the electric field is reduced.
(b)   only the magnetic field is reduced.
(c)   both the electric and magnetic field are reduced.

### QUESTION 22*

If the initial intensity of the unpolarized light is I0, what is the intensity I3 transmitted by the stack?

(a)   I3 = 0
(b)   I3 = I0 / 2
(c)   I3 = I0 / 4
(d)   I3 = I0 / 8
(e)   I3 = I0 / 16

### QUESTION 23*

An AC-transformer consists of two coils. The primary winding has 100 turns and the secondary has 1000 turns. The current in the primary is 2 A. What is the current in the secondary?

(a)   0.02 A
(b)   0.2 A
(c)   1 A
(d)   2 A
(e)   20 A

### QUESTION 24***

This and the next question pertain to the following situation.

A uniform magnetic field B permeates a region of space as indicated in the shaded region of the figure below. The direction of B is into the paper. Each of the wire loops is moving with an identical speed v, but with velocity oriented in different directions, as indicated in the figure.

Which of the wire loops experiences a force towards the top of the page due to the magnetic field?

(a)   X only
(b)   Y only
(c)   W only
(d)   Z only
(e)   X and W

### QUESTION 25*

Which of the wire loops has the greatest induced emf at the instant shown above?

(a)   X
(b)   Y
(c)   Z

### QUESTION 26**

This and the next question pertain to the following situation.

This loop has 200 turns of wire with resistance 0.3 Ω/m. It is turned at a steady rate and dissipates energy with a peak power of 100 W. The external magnetic field is constant and the current I flows around the loop in the direction indicated in the figure at the instant shown.

What is the peak emf generated in the loop?

(a)   23 V
(b)   55 V
(c)   100 V
(d)   173 V
(e)   284 V

### QUESTION 27**

As viewed from below, the direction of rotation of the loop is

(a)   clockwise (that is, AD comes out of the page at the instant shown).
(b)   counter-clockwise (that is, AD goes into the page at the instant shown).

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.