### Fall 2007 Physics 102 Hour Exam 2(25 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 107. The exam period was 90 minutes; the mean score was 85.4; the median was 88. Click here to see page1 page2 page3 of the formula sheet that came with the exam.

• A reminder about prefixes: p (pico) = 10-12; n (nano) = 10-9; μ (micro) = 10-6; m (milli) = 10-3; k (kilo) = 10+3; M or Meg (mega) = 10+6; G or Gig (giga) = 10+9.

### QUESTION 1**

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

A particle of mass 3 × 10-8 kg, negative charge -20 μC, and velocity v = 2000 m/s enters an area with magnetic field B1 perpendicular to the plane of the paper. The direction and magnitude of B1 are not given. The particle performs a quarter-circle trajectory and penetrates an area with a different magnetic field B2 perpendicular to the plane of the paper. In this area it performs a half-circle trajectory. The direction and magnitude of B2 are not given.

What is the direction of the magnetic field B1?

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

### QUESTION 2**

What is the direction of the magnetic field B2?

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

### QUESTION 3*

What is the magnitude of the magnetic field B1?

(a)   B1 = 1 T
(b)   B1 = 1.2 T
(c)   B1 = 3 T
(d)   B1 = 3.6 T
(e)   B1 = 5 T

### QUESTION 4*

Compare the relative magnitudes of B1 and B2.

(a)   B1 < B2
(b)   B1 = B2
(c)   B1 > B2

### QUESTION 5**

This and the next question pertain to the diagram below.

A rod of length 30 cm and resistance R2 = 3 Ω is placed on frictionless vertical slides, which are connected to an electromotive force ε = 12 V and resistance R1 = 7 Ω. A magnetic field B = 8 T is present, perpendicular to the plane of the page.

If the rod is at rest, what is the direction of B?

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

### QUESTION 6**

What is the mass of the rod m?

(a)   m = 0 kg
(b)   m = 0.058 kg
(c)   m = 0.29 kg
(d)   m = 1.5 kg
(e)   m = 2900 kg

### QUESTION 7**

This and the next question pertain to the diagram below.

A rod of length 30 cm and resistance R2 = 3 Ω is placed on frictionless vertical slides, which are connected to an electromotive force ε and resistance R1 = 7 Ω. A magnetic field B = 8 T is present, pointing out of the plane of the page. The rod is now moved downwards at a constant velocity v = 2 m/s.

Which way does the current flow through the rod?

(a)   to the left
(b)   to the right
(c)   There is no current through the rod.

### QUESTION 8**

What is the current through the rod I*?

(a)   I* = 0 A
(b)   I* = 0.24 A
(c)   I* = 0.48 A
(d)   I* = 2.4 A
(e)   I* = 10 A

### QUESTION 9*

This and the next two questions refer to the figure below.

A particle of charge +q moves at a velocity v in a magnetic field B, directed at the +x direction.

What is the direction of the acceleration a of the particle if v is also in the +x direction?

(a)   a = 0
(b)   a is in the +x direction.
(c)   a is in the +y direction.
(d)   a is in the -y direction.
(e)   a is directed out of the page.

### QUESTION 10*

What is the direction of the acceleration a of the particle if v is in the -y direction?

(a)   a = 0
(b)   a is in the +x direction.
(c)   a is in the -y direction.
(d)   a is directed into the page.
(e)   a is directed out of the page.

### QUESTION 11*

What is the direction of the acceleration a of the particle if v is directed out of the page?

(a)   a = 0
(b)   a is in the +x direction.
(c)   a is in the +y direction.
(d)   a is in the -y direction.
(e)   a is directed out of the page.

### QUESTION 12*

This and the next two questions refer to the figure below.

A triangular loop carries a current I = 12 A. A magnetic field is present, B = 0.2 T. The loop lies in the x-y plane and the magnetic field B points in the x direction.

What is the magnetic force F1 acting on the right side of the loop?

(a)   F1 = 0
(b)   F1 = 1.8 N into the page.
(c)   F1 = 1.8 N out of the page.
(d)   F1 = 2.5 N into the page.
(e)   F1 = 2.5 N out of the page.

### QUESTION 13*

What is the magnetic force F2 acting on bottom side of the loop?

(a)   F2 = 0
(b)   F2 = 1.8 N into the page.
(c)   F2 = 1.8 N out of the page.
(d)   F2 = 2.5 N into the page.
(e)   F2 = 2.5 N out of the page.

### QUESTION 14**

What is the magnetic force F3 acting on the left side of the loop, the hypotenuse of the triangular loop?

(a)   F3 = 0 N
(b)   F3 = 1.8 N into the page.
(c)   F3 = 1.8 N out of the page.
(d)   F3 = 2.5 N into the page.
(e)   F3 = 2.5 N out of the page.

### QUESTION 15*

This and the next two questions refer to the figure below.

A mechanical crank is used to turn a rectangular loop of area 0.30 m2 at angular frequency ω = 2πf in the presence of a magnetic field B = 0.4 T as shown. The 150 V peak EMF produced in the loop results in a peak primary voltage in the 125 turn primary coil of the transformer of Vp = 150 V. The secondary windings (375) are connected to an oscilloscope with the voltage display shown. The peak current in the secondary coil is 35 mA.

What is the peak voltage in the secondary, Vs?

(a)   Vs = 50 V
(b)   Vs = 150 V
(c)   Vs = 450 V

### QUESTION 16**

What is the period of the oscillating voltage in the secondary circuit?

(a)   T = 2.3 ms
(b)   T = 3.6 ms
(c)   T = 4.1 ms
(d)   T = 5.0 ms
(e)   T = 7.8 ms

### QUESTION 17*

What is the peak current through the primary coil?

(a)   Ip = 12 mA
(b)   Ip = 35 mA
(c)   Ip = 105 mA

### QUESTION 18*

This and the next three questions pertain to the 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 line in the drawing.

At the instant shown in the diagram, the voltage across the inductor is.

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

### QUESTION 19**

This circuit is being driven __________ the resonant frequency

(a)   faster than
(b)   slower than
(c)   at

### QUESTION 20*

A local radio station broadcasts at the frequency 107.1 MHz (107.1 × 106 Hz). If the tuner of your radio involves an RLC circuit with an inductance L = 3 × 10-6 H, to obtain what capacitance C should you adjust the knob on your radio to hear this radio station?

(a)   7.4 × 10-13 F
(b)   1.1 × 10-12 F
(c)   4.8 × 10-12 F

### QUESTION 21**

In an AC circuit, the peak voltage across the generator is always greater than the peak voltage across the capacitor.

(T)   True
(F)   False

### QUESTION 22*

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

The RLC circuit below is being driven by an AC source with frequency f = 39.8 Hz 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 = 28 volts

### QUESTION 23*

Calculate V0 the maximum voltage across the generator.

(a)   V0 = 12.5 volts
(b)   V0 = 13.5 volts
(c)   V0 = 15.3 volts
(d)   V0 = 28.4 volts
(e)   V0 = 33.2 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***

If the frequency of the generator was increased slightly while keeping the generator maximum voltage the same, would the maximum voltage across the resistor increase, remain the same or decrease?

(a)   increase
(b)   remain the same
(c)   decrease

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.