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 111. The exam period was 90 minutes; the mean score was 75.6; the median was 77. Click here to see page1 page2 page3 of the formula sheet that came with the exam.

Some helpful information: • 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}.

(a) moves in a circle at the initial speed (b) moves in a helix along the initial direction with radius 3.7 m (c) moves in a helix along the initial direction with radius 2.2 m (d) moves in a helix along the z direction with radius 3.7 m (e) moves in a helix along the z direction with radius 2. m

(a) attract each other. (b) repel each other. (c) not exert force on each other.

A DC voltage of 12 V is applied to the primary coil. What is the expected amplitude of V_{out}?

(a) 24 V (b) 12 V (c) 6 V (d) 3 V (e) 0

A square loop consisting of 10 turns with sides equal to 1 cm carrying a current of 2 A is situated at the center of a solenoid with 100 turns per meter. The normal to the square loop is tilted at an angle 30° from the solenoid's longitudinal axis. What is the magnitude of the torque on the loop when a current of 3 A passes through the solenoid?

(a) 1.9 × 10^{-7} N-m (b) 3.8 × 10^{-7} N-m (c) 4.4 × 10^{-7} N-m (d) 3.8 × 10^{-5} N-m (e) 4.4 × 10^{-5} N-m

(a) 5.3 × 10^{-3} rad/s (b) 13 rad/s (c) 53 rad/s (d) 5300 rad/s (e) 1.3 × 10^{5} rad/s

An electron travels in a straight line in the presence of constant electric and magnetic fields.

How are the electric and magnetic fields aligned?

(a) perpendicular to each other (b) parallel to each other (c) with a 45° angle between two vectors

(a) 2 m/s (b) 50 m/s (c) 5 m/s (d) 15 m/s (e) 0.5 m/s

The electric load of a set of apartments can be represented by a resistor. The resistor is connected to a transformer, as shown in the diagram. The primary of the transformer is connected to the city's power distribution network, rated at V_{pri-max} = 13.2 kV, and the secondary is supplying V_{sec-max} = 230 V to the apartments. The frequency in this AC circuit is 60 Hz.

The primary coil of the transformer is made using N_{p} = 26,400 turns. What is the number of turns of the secondary coil?

(a) 13200 (b) 110 (c) 460

(a) 20 A (b) 115 A (c) 1150 A (d) 13200 A (e) 264500 A

(a) 32 A (b) 5600 A (c) 19 kA

A square loop of wire of length 10 cm on a side and with resistance R = 2 Ω lies in the x-y, plane in a region of space containing a uniform magnetic field B pointing out of the page (in the z-direction). The magnetic field has a time dependence as shown in the graph, going to zero at t = 10 sec, and reversing direction for t > 10 sec.

What is the current in the loop at time t = 10 sec?

(a) 0 A (b) 1 mA (c) 2 mA (d) 5 mA (e) 10.0 mA

(T) True (F) False

A bar magnet falls from point A to point B through a solenoid with its ends connected. The solenoid is made of steel wire with resistance per unit length of 1 Ω/cm.

How does the speed of the magnet at point B compare to what it would be if the solenoid were not there?

(a) It is greater. (b) It is less. (c) It stays the same.

(a) (b) (c)

In the first experiment a particle of mass m, charge q and velocity v enters a region with magnetic field B perpendicular to the plane of the paper. The particle performs a half circle trajectory and exits the region after time t at a distance d from the entrance point.

In the second experiment the particle has mass 2m. The charge, velocity and magnetic field stay unaltered. What distance from the entrance point will the particle exit the region?

(a) 2d (b) d (c) d / 2

(a) t (b) 2t (c) t / 2

(a) positive. (b) negative.

A conducting rod of finite resistance and length L moves down frictionless vertical wires at a constant velocity v. The wires are connected across a capacitor. A uniform magnetic field B is present everywhere, pointing into the page as indicated.

Which plate of the capacitor is positively charged?

(a) right one (b) left one

(a) 45 μC (b) 18 μC (c) 5.0 μC (d) 3.2 μC (e) 1.8 μC

An inductor is made from a wire-wound cylindrical solenoid of radius 2.5 mm, length 1 cm, and containing 1000 turns of wire. A current I = 50 mA flows through the wire.

Calculate the inductance L of the solenoid.

(a) 0.25 nH (b) 2.5 μH (c) 2.5 mH

(a) 0 μJ (b) 3.1 μJ (c) 62.5 μJ

(a) 0.25 nH (b) 2.5 nH (c) 2.5 μH (d) 25 μH (e) 2.5 mH

A rectangular loop of wire lies in the x-y plane as shown below and it carries a current of 2.5 A. The sides a-b and c-d are parallel to the x-axis and are of length 6 cm while the sides a-d and b-c are of length 5 cm and parallel to the y-axis. The loop sits in a constant uniform magnetic field B.

Along what direction should the magnetic field be applied for the force on segment a-d to be zero, but for the force on a-b and the torque on the loop to be non-zero (F_{ad} = 0, F_{ab} ≠ 0, τ ≠ 0)?

(a) along the x-axis (b) along the y-axis (c) along the z-axis (d) in the x-z plane at 45° to the z-axis (e) no such situation is possible

(a) 16 N-m (b) 3.7 N-m (c) 0.235 N-m (d) 0.011 N-m (e) 0.007 N-m

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