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 101. The exam period was 90 minutes; the mean score was 69.6; the median was 75. Click here to see page1 page2 of the formula sheet that came with the exam.

A 30-cm-long conducting rod (rod A) with mass 10 g is suspended by conducting wires of negligible mass as shown in the figure. The rod is 10 cm above the surface of a table. On the table, there is another long rod (rod B) parallel to rod A. Rod B is carrying a current of 200 A.

What is the minimum current in rod A necessary to support the weight of the rod so that there is no tension in the wires?

(a) 51 A (b) 102 A (c) 204 A (d) 408 A (e) 817 A

(T) True (F) False

Two particles, A (m_{A}=1.7 × 10^{-27} kg , Q_{A}= 1.6 × 10^{-19 }C ) and B (m_{B}= 3.4 × 10^{-27} kg , Q_{B}= -3.2 × 10^{-19 }C ) enter a box with uniform magnetic field B=7.5 T. Particle A enters with velocity v_{A}=10^{6} 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

(a) L = 2.84 × 10^{-3} m (b) L = 3.75 × 10^{-3} m (c) L = 4.25 × 10^{-3} m

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

A U-shaped conducting rod is connected to two conducting wires at points A and B as shown in the figure below. The rod is allowed to rotate about an axis connecting the pivot points A and B. A current of 3.5 A passes through the wires and the rod (as indicated by short arrows). A uniform B field of 0.04 T is applied along a direction at 45° angle with the sides of the rod. The length of each segment of the rod is 50 cm.

What is the magnitude of the magnetic force on left side (segment AD) of the rod?

(a) 0 N (b) 0.0700N (c) 0.0495N (d) 0.0350N (e) 0.0990N

(a) left: out of the page, right: into the page (b) left: into the page, right: out of the page (c) left: out of the page, right: out of the page

(a) 0 Nm (b) 0.0495 Nm (c) 0.0247 Nm

A rectangular wire loop is carried in the y-direction at a constant speed of 10 m/s. The loop has a total loop resistance of 10 Ω and is lying in the x-y plane. It is 30 cm long and 10 cm wide. A region of constant and uniform magnetic field of magnitude 10 T pointing in the positive z-direction extends from y = 0 to y = 60 cm as indicated in the figure. At time t = 0 the leading edge of the loop enters the magnetic field region.

From t = 0 to t = 0.03 sec a counter clockwise current flows in the circuit.

(a) 5.0 W (b) 10.0 W (c) 20.0 W (d) 40.0 W (e) 100.0 W

(a) A negative amount of work is done pulling the loop out of the field region during this time interval. (b) The same amount of work is done pulling the loop out of the field region as pulling it into the field region. (c) Less work would be done if the loop were pulled through at a faster speed.

A coil consisting of two square loops, connected in series, rotates at f = 60 revolutions per second, that is ω = 2π radians/sec. It does so around the y-axis and through a magnetic field of 1 Tesla pointing in the positive z-direction. A snapshot of the rotating coil at time t=0 is shown in the figure. At time t=0 the plane of the coil is in the x-y plane. The loops are 10 cm by 10 cm in dimension and have no resistance of their own. A 1 Ω resistor is connected across the coils as shown.

At time t = 0 (shown in the figure)

(a) the current in the loops is flowing clockwise. (b) the current in the loop is flowing counter clockwise. (c) the current is zero.

(a) 1.20 amp (b) 3.77 amp (c) 7.54 amp (d) 56.85 amp (e) 113.70 amp

An ideal transformer with 5 turns on the primary and 10 turns on the secondary is shown in the figure. A sinusoidal voltage source having V(t) = 10 sin(100t) volts is connected across the primary and a 1 Ω resistor is connected across the secondary.

The current in the secondary oscillates at 200 rad/sec.

(a) 2.0 amp (b) 5.0 amp (c) 10.0 amp (d) 20.0 amp (e) 40.0 amp

A uniform magnetic field is pointed in the z-direction and has a time dependence as shown in the figure. It is zero at t = 0 as well as at t = 24 sec. Between 10 and 18 sec it is 1 T, and for t > 30 sec it is -1 T. A square conducting coil of length 10 cm on a side lies in the x-y plane. The resistance of the coil is 10 Ω.

At t = 24 sec which statement is true?

(a) No current flows in the loop. (b) A counter-clockwise current flows in the loop. (c) A clockwise current flows in the loop.

(a) 10.0 μA (b) 3.14 μA (c) 33.3 μA (d) 50.0 μA (e) 100.0 μA

(a) 14.14 V (b) 20.00 V (c) 40.00 V

Which of the graphs below best illustrates the energy U_{L} in the inductor as a function of time?

(a) (b) (c)

In which one of the phasor diagrams is the voltage across the resistor greatest?

Which one of the following graphs best illustrates the voltage across the inductor as a function of time?

The ratio of the inductances for the 20 cm and 10 cm inductors L_{20} / L_{10} is 4 / 1 .

When the generator frequency f is tuned so that the capacitive and inductive reactances are equal, what is the maximum current I flowing in the circuit?

(a) I = 1.00 × 10^{-7} A (b) I = 6.28 × 10^{-3} A (c) I = 1.01 × 10^{-2} A (d) I = 1.00 × 10^{-1} A (e) I = 3.14 × 10^{-2} A

The generator frequency f is set to 7000 Hz. What is the magnitude of the phase difference (in degrees) between the current in the circuit and the generator's voltage?

(a) Φ = 0.238° (b) Φ = 11.99° (c) Φ = 102.23° (d) Φ = 121.25° (e) Φ = 166.72°