### Fall 2004 Physics 102 Hour Exam 2(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 119. The exam period was 90 minutes. The mean score was 98.5; the median was 103. Click here to see page1 page2 of the formula sheet that came with the exam.

### QUESTION 1*

In the circuit shown here, the maximum voltage across the 10-5 H inductor is 0.1 V. What is the maximum current in the circuit?

(a)   26.5 A
(b)   33.3 A
(c)   45.1 A
(d)   56.7 A
(e)   67.7 A

### QUESTION 2*

What is the equivalent impedance of the capacitor, inductor, and resistor in series in the circuit shown here?

(a)   101 Ω
(b)   155 Ω
(c)   198 Ω
(d)   218 Ω
(e)   333 Ω

### QUESTION 3*

Lisa Simpson wants to contact aliens on a distant planet using a radio. Inside the radio is a resonant circuit, which is shown below.

The aliens set their receiver to listen for signals at a frequency of 10 MHz. To what value should Lisa tune the inductor so that the circuit inside her radio is resonant at the same frequency?

(a)   2.53 × 10-9 H
(b)   3.85 × 10-9 H
(c)   4.51 × 10-9 H
(d)   5.89 × 10-9 H
(e)   7.70 × 10-9 H

### QUESTION 4*

When Lisa’s radio is broadcasting at 10 MHz, the maximum current through the resistor is 0.1 A. What is the average power dissipated in the circuit?

(a)   0.111 W
(b)   0.250 W
(c)   0.458 W
(d)   0.611 W
(e)   0.999 W

### QUESTION 5*

What is the maximum voltage across the capacitor if the maximum current through the resistor is 0.1 A?

(a)   0.0102 V
(b)   0.0111 V
(c)   0.0159 V
(d)   0.153 V
(e)   0.557 V

### QUESTION 6**

When the voltage across the resistor is at a maximum in the 10 MHz cycle, the magnitude of the voltage across the capacitor is

(a)   at a minimum.
(b)   neither at a maximum or a minimum.
(c)   at a maximum.

### QUESTION 7***

If Lisa keeps the same inductor, capacitor, and resistor (so that the circuit is resonant at 10 MHz), but switches out the voltage generator for one at 20 MHz with the same Vmax, the maximum current in the circuit

(a)   decreases.
(b)   stays the same.
(c)   increases.

### QUESTION 8*

A solenoid is wound with 100 turns of wire on a plastic cylinder that is 10 cm long and has a 2 cm diameter. If the diameter of the cylinder is doubled, but the length of the cylinder and the number of turns of wire are kept fixed, then the self-inductance of the solenoid

(a)   decreases by half.
(b)   stays the same.

### QUESTION 9*

Your microwave oven uses a resonant circuit, which is shown here. The frequency used by the microwave oven is the same frequency used by the wireless network in your dorm room. To prevent interference, you decide to alter the circuit in the oven and change its resonant frequency. You can do this by adding another capacitor. To decrease the resonant frequency, should you add the capacitor in series or in parallel to the capacitor already in the circuit?

(a)   parallel
(b)   series

### QUESTION 10*

Vertically polarized light is incident on a combination of polarizers, as in this figure. For which combination will the most light be transmitted?

(a)
(b)
(c)

### QUESTION 11*

The light emitted by the sun takes 8 minutes and 20 seconds to reach us. How far is the sun from us?

(a)   50 million kilometers
(b)   100 million kilometers
(c)   150 million kilometers

### QUESTION 12*

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

Two particles, A (mA=1.7 ×10-27 kg , QA= 1.6 × 10-19 C ) and B (mB= 3.4 × 10-27 kg , QB= -3.2 × 10-19 C ) enter a box with uniform magnetic field B= 6 T. Particle A enters with velocity v =108 m/s and follows trajectory A.

What is the direction of the magnetic field inside the box?

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

### QUESTION 13**

Particle B also enters with velocity v = 108 m/s. Which trajectory will it follow?

(a)   trajectory 1
(b)   trajectory 2
(c)   trajectory 3

### QUESTION 14*

The distance L, from entry to the point where trajectory A exit the spectrometer is

(a)   L = 0.115 m
(b)   L = 0.354 m
(c)   L = 0.637 m
(d)   L = 1.43 m
(e)   L = 1.75 m

### QUESTION 15*

This and the next question pertain to the following situation.

A rectangular loop of wire is located near a long, straight wire that carries a current of 6 A flowing to the right (see the figure). The current in the loop Iloop = 8 A is flowing clockwise.

The loop of wire is attracted to the long straight wire.

(T)   True
(F)   False

### QUESTION 16**

The magnitude of the net force on the entire loop is

(a)   |F| = 0 N
(b)   |F| = 1.44 × 10-5 N
(c)   |F| = 6.89 × 10-5 N
(d)   |F| = 3.65 × 10-4 N
(e)   |F| = 8.72 × 10-4 N

### QUESTION 17**

This and the next question pertain to the following situation.

Two fixed conductors are connected by a resistor R = 20 Ω . The two fixed conductors are separated by L = 2.5 m and lie vertically, parallel to the gravitational field (g = 9.8 m/s2). A moving conductor of mass m slides on them (without friction) falling at a constant speed v = 6 m/s. Out of the page is a magnetic field (shown by the black dots in the figure) with a magnitude of 5 T.

In which direction does the current flow through the moving conductor?

(a)   to the right
(b)   to the left

### QUESTION 18*

What is the magnitude of the current?

(a)   1.37 A
(b)   2.44 A
(c)   3.75 A
(d)   4.98 A
(e)   5.39 A

### QUESTION 19**

This and the next question pertain to the following situation.

In the figure is shown a square loop (L=2 m) of wire in edge view, which is free to rotate around an axis O (perpendicular to the page). The loop consists of 12 loops of wire and the normal to the loops forms an angle of 30° to the vertical. An external battery (not shown) causes a current I=6 amps to flow around the loop. The external magnetic field directed down (B=6 T) creates a clockwise torque on the current loop.

What is the direction of the current in side A (which runs normal to the page)?

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

### QUESTION 20*

What is the magnitude of the torque?

(a)   348 N m
(b)   487 N m
(c)   620 N m
(d)   735 N m
(e)   864 N m

### QUESTION 21*

This and the next question pertain to the following situation.

This figure illustrates a plane electromagnetic wave.

Compare the z-component of the electric field at the points a, b and c.

(a)
(b)
(c)

### QUESTION 22*

What is the direction of propagation of this plane electromagnetic wave?

(a)   +x-direction
(b)   +y-direction
(c)   +z-direction

### QUESTION 23*

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

The figure below shows wires wrapped around an iron core. Coil A has 10 turns, and coil B has 5 turns. This serves as an ideal transformer between an AC generator and a resistor. The resistance R = 9 Ω. The average power dissipated in the resistor is P = 90 W.

What is the maximum current through the resistor?

(a)   2.52 A
(b)   4.47 A
(c)   6.95 A
(d)   8.41 A
(e)   10 A

### QUESTION 24*

What is the rms voltage of the generator?

(a)   49.2 V
(b)   56.9 V
(c)   63.3 V
(d)   78.5 V
(e)   90 V

### QUESTION 25**

If the average power dissipated by the resistor were 180 W instead of 90 W, with the same generator, the same resistor, and the same number of turns in coil B, the number of turns in coil A should be

(a)   less than 10 turns
(b)   equal to 10 turns
(c)   more than 10 turns

### QUESTION 26*

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

A loop with 200 turns of wire is placed into a constant horizontal magnetic field B, as shown in the figure below. It is turned at a steady rate of 500 rad/sec and generates a maximum voltage of 160 V. The loop has a total resistance of 90 ohms. The loop rotates in the direction indicated by the curved arrow.

What is the magnitude of the magnetic field B?

(a)   0.0231 T
(b)   0.0424 T
(c)   0.0625 T
(d)   0.0891 T
(e)   0.102 T

### QUESTION 27*

If there were 100 turns instead of 200 turns in the loop, the maximum voltage would be is

(a)   smaller than 160 V
(b)   equal to 160 V
(c)   larger than 160 V

### QUESTION 28*

If the loop with 200 turns was turned at the same steady rate of 500 rad/sec, but in the direction opposite to that indicated by the curved arrow, the maximum voltage would be

(a)   smaller than 160 V.
(b)   equal to 160 V.
(c)   larger than 160 V.

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.