Spring 2003 Physics 102 Hour Exam 2
(26 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 26 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 94. When the exam was given, the mean was 74.7; the median was 78. Click here to see page1 page2 of the formula sheet that came with the exam.


QUESTION 1*

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

A conducting bar can slide along two fixed conductors which are separated by 1.3 m and connected by a resistor R = 12 Ω. A uniform magnetic field of 2.1 tesla points out of the page. The bar is allowed to fall due to gravity. The current passing through the circuit is measured to be 23 amperes.

What is the mass of the bar?

(a)   1.4 kg
(b)   3.3 kg
(c)   4.7 kg
(d)   5.1 kg
(e)   6.4 kg


QUESTION 2*

How fast is the bar falling?

(a)   98 m/s
(b)   101 m/s
(c)   115 m/s
(d)   127 m/s
(e)   133 m/s


QUESTION 3**

If the resistance is increased to 50 Ω what happens to the speed at which the bar falls?

(a)   Does not change.
(b)   Increases.
(c)   Decreases.


QUESTION 4**

A conducting ring is entering into a region of uniform magnetic field that points into the page, as shown in the figure. In which direction will the induced current flow within the ring?

(a)   
(b)   
(c)   


QUESTION 5**

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

Three parallel wires carry currents, equal in magnitude (I1 = I2 = I3 = 3 A) in the directions as shown.

What is the magnitude of the magnetic field at point x (0.5 meter below wire #1)?

(a)   9.2 × 10-6 T
(b)   8.5 × 10-6 T
(c)   5.3 × 10-6 T
(d)   2.1 × 10-6 T
(e)   1.5 × 10-6 T


QUESTION 6*

What is the direction of the magnetic field at this point?

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


QUESTION 7*

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

(a)   up
(b)   there is none
(c)   down


QUESTION 8*

A beam of Helium nuclei (charge +3.2 × 10-19 C, mass 6.64 × 10-27 kg) are traveling at 2 × 105 m/s. What strength must the magnetic field be for them to travel in a circular path of 2 meters in radius?

(a)   1.24 × 10-3 T
(b)   2.08 × 10-3 T
(c)   3.89 × 10-3 T


QUESTION 9*

This and the next question pertain to the following situation.

A long solenoid with 300 turns, a length of 0.25 meters, and a diameter of 2 cm has 100 mA of current passing through it in the direction shown below.

What is the magnetic field inside the solenoid?

(a)   9.83 × 10-5 T
(b)   1.51 × 10-4 T
(c)   6.00 × 10-4 T


QUESTION 10*

Which direction is the field pointing?

(a)   to the left
(b)   to the right


QUESTION 11**

The phasor diagram shown below gives information on a particular series RLC circuit. It is completely unlabeled, but you should know from examining it the proper quantity that is referred to by each line. The frequency of this generator is

(a)   smaller than the resonant frequency.
(b)   equal to the resonant frequency.
(c)   larger than the resonant frequency.


QUESTION 12*

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

A square loop of wire, measuring 4 cm on each side is oriented in a 1.2 T magnetic field as shown. The loop has 0.35 amps flowing through it in a counter-clockwise direction. It is free to move in any direction.

How will the loop move in the field?

(a)   to the left
(b)   to the right
(c)   rotate so that the left side comes out of the page and the right goes in
(d)   rotate so that the right side comes out of the page and the left goes in
(e)   it doesn’t move


QUESTION 13*

If the loop is now fixed so that it can only pivot about the center of the loop on the vertical axis, what will the torque, τ0, be on the loop?

(a)   τ0 = 3.36 × 10-4 N-m
(b)   τ0 = 5.28 × 10-4 N-m
(c)   τ0 = 6.72 × 10-4 N-m


QUESTION 14**

Let τ0 be the answer to the previous question. If the loop is rotated 30° as shown below, what is the new torque?

(a)   τ0 sin(60°)
(b)   τ0 sin(30°)
(c)   τ0


QUESTION 15*

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

Consider the AC circuit shown below. The current through the generator is I(t) = 2.5 sin(377 t) amps.

Calculate Vc, the peak voltage across the capacitor.

(a)   Vc = 375 volts
(b)   Vc = 442 volts
(c)   Vc = 5655 volts


QUESTION 16*

Calculate UL the peak energy stored in the inductor.

(a)   UL = 0.594 J
(b)   UL = 1.24 J
(c)   UL = 2.49 J


QUESTION 17*

Calculate Vgen the peak voltage across the generator.

(a)   Vgen = 375 volts
(b)   Vgen = 423 volts
(c)   Vgen = 458 volts
(d)   Vgen = 823 volts
(e)   Vgen = 911 volts


QUESTION 18***

Calculate the voltage across the inductor at the time t = 0.

(a)   VL(0) = 0 volts
(b)   VL(0) = 78 volts
(c)   VL(0) = 179 volts


QUESTION 19*

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

Unpolarized light with intensity I0 is incident on a stack of three linear polarizers with transmission axis oriented as shown below.

Calculate I2, the intensity of the light transmitted by the first two polarizers.

(a)   I2 = 0
(b)   I2 = ½ I0 cos2(30°)
(c)   I2 = ½ I0 cos2(60°)


QUESTION 20*

Calculate I3, the intensity of the light transmitted by the entire stack of polarizers.

(a)   I3 = 0
(b)   I3 = I2 cos2 (30°)
(c)   I3 = I2 cos2 (60°)


QUESTION 21**

If the middle polarizer is rotated from an angle of 30° down to an angle of 60°, the intensity of light transmitted by the entire stack will

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


QUESTION 22*

This and the next question pertain to the following situation.

A mechanical crank is used to turn a rectangular loop with area 0.33 m2 at angular frequency ω in the presence of a magnetic field B = 0.8 T as shown. The 200 V peak EMF produced in the loop results in a peak voltage across the primary of the transformer of Vp = 200 V. The secondary windings are connected to an oscilloscope, and the peak voltage is 100 volts.

If the primary coil has 100 windings, how many windings are there in the secondary coil? (Note number of windings on picture is not accurate!)

(a)   Ns = 50
(b)   Ns = 100
(c)   Ns = 200


QUESTION 23**

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 = 8.3 ms
(e)   T = 9.8 ms


QUESTION 24**

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

The electric field of an electromagnetic wave is given by the expression E(x,y,z,t) = 125 sin(15y - ωt) z volts/meter (in the z-direction).

Determine the wavelength λ of this electromagnetic wave.

(a)   λ = 0.419 m
(b)   λ = 15 m
(c)   λ = 125 m


QUESTION 25**

What is the direction of the magnetic field associated with this wave?

(a)   x
(b)   y
(c)   z


QUESTION 26**

Calculate the average energy density in the magnetic field of this wave.

(a)   0.75 × 10-8 J/m3
(b)   1.90 × 10-8 J/m3
(c)   3.45 × 10-8 J/m3