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 126.
The exam period was 90 minutes; the mean score was 94.7; the median was
95. Click here to see page1
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.
Two long straight parallel wires are separated by a distance of 3 m. One
wire carries a current of 3 A. The other carries a current of 2 A. Both
currents run in the same direction.
What is the magnitude of the force on 1 meter of the wire carrying 3
A, due to current in the other wire?
(a) 7 × 10-8 N
(b) 1 × 10-7 N
(c) 4 × 10-7 N
(d) 7 × 10-7 N
(e) 2 × 10-6 N
(b) 1.3 × 10-7 T
(c) 4.0 × 10-7 T
(d) 5.7 × 10-7 T
(e) 6.2 × 10-7 T
A long section of straight wire carrying a current runs parallel to
the surface of the earth on the east-west axis. It has a linear mass
density of 10 g/m. The earth's magnetic field is approximately 50 μT
and points south to north.
What current must the wire carry to balance the force of gravity
(i.e. the wire will remain suspended above the ground) ?
(a) 2 kA
(b) 32 kA
(c) 90 kA
(d) 120 kA
(e) 2 MA
(a) east to west
(b) west to east
(c) It doesn't matter.
A hemoglobin protein, of mass 10-19 g and charge
+3e (three times the charge of the electron), is shot at a
velocity v = 60 m/s into a region with a uniform magnetic field
0.5 T (here pointing out of the page).
What is the displacement L?
(a) 1.3 cm
(b) 2.5 cm
(c) 5.0 cm
(d) 10 cm
(e) 12 cm
(a) 0.66 ms
(b) 1.3 ms
(c) 2.6 ms
(d) 5.2 ms
(e) 7.2 ms
A circular loop of radius R = 0.25 m is rotated at a frequency
f = 10 Hz in a uniform magnetic field B = 0.2 T, pointing
to the right.
What is the magnitude of the induced EMF when the loop is at the
state shown here?
(a) 0 V
(b) 1.38 V
(c) 2.14 V
(d) 3.74 V
(e) 4.89 V
(a) when the angle between the surface normal (to the loop) and the field is 0°
(b) when the angle between the surface normal (to the loop) and the field is 90°
(c) The EMF is constant.
(a) 0.21 m
(b) 0.42 m
(c) 1.77 m
(d) 2.95 m
(e) 4.8 5 m
(a) attract each other.
(b) repel each other.
(c) not exert force on each other.
A rectangular loop with side lengths a = 4 m and b = 5
m is in a constant magnetic field, pointing into the page. The loop has
a resistivity per unit length of 15 Ω/m.
The magnetic field strength begins to decrease at a rate of 0.2
T/sec. What is the magnitude of the induced current in the loop?
(a) 0 A
(b) 1.3 × 10-4 A
(c) 1.5 × 10-2 A
(d) 0.1 A
(e) 3.4 A
(a) decreasing at 0.2 T/sec
(b) decreasing at 0.1 T/sec
(d) increasing by 0.1 T/sec
(e) increasing by 0.2 T/sec
Neglect the force due to gravity in these four
A charged particle is undergoing circular motion in a magnetic field.
Its velocity, its acceleration and the magnetic field are best described
by which one of the following statements?
(a) v and a are parallel to each other, B perpendicular to both.
(b) v and B are parallel to each other, a is perpendicular to both.
(c) a and B are parallel to each other, v is perpendicular to both.
(d) All three are parallel to each other.
(e) All three are perpendicular to each other.
(a) a cube
(b) a cone
(c) a helix
(d) a straight line
(e) a circle
(a) stay the same.
(e) become one quarter.
A mad scientist causes a giant magnetic field to be erected all over the
quad, directly upward. You are playing Frisbee using a resistive
circular loop of wire. You stand just outside the quad while your
friend is inside.
After playing for a while, you notice the Frisbee is getting warm.
(a) The magnetic field makes the air around the Frisbee hotter, heating the Frisbee.
(b) The radiation caused by the magnetic field cooks the Frisbee.
(c) Current is induced by the magnetic field, heating the Frisbee.
(a) 12.1 Tm2
(b) 30 Tm2
(c) 45 Tm2
(d) 78 Tm2
(e) 90 Tm2
A particle of mass 3 × 10-8 kg, negative charge -20
μC, and velocity v = 2000 m/s enters a region 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 enters another
region with a different magnetic field B2
perpendicular to the plane of the paper. In this region, it performs a
semi-circular trajectory. The direction and magnitude of
B2 are not given.
What is the direction of the magnetic field
(a) into the page
(b) out of the page
(a) B1 = 1 T
(b) B1 = 1.2 T
(c) B1 = 3 T
(d) B1 = 3.6 T
(e) B1 = 5 T
(a) B1 < B2
(b) B1 = B2
(c) B1 > B2
A conducting rod of length L and mass m slides down
frictionless vertical wires at a constant velocity v. The wires
are connected across a light bulb. A uniform magnetic field B is
present everywhere, pointing into the page as indicated. Assume the rod
and wires are perfect conductors, and that gravity is present.
Which way does the current flow?
(a) 4.9 mΩ
(b) 9.8 mΩ
(c) There is not enough information to answer this question.