SP212 Exam 4
Name:
1) Do not open this exam until instructed to do so.
2) This exam consists of 13 multiple choice questions. Clearly circle your answers.
3) For some questions, relevant information might be given in the included figure.
4) You have 50 minutes to complete this exam.
5) Do not interact with anyone except Dr. Rittenhouse during the exam.
6) Do not discuss this exam with any other students who have not taken the exam.
7) When you have completed the entire exam, write your final answers on the answer sheet provided. Be
sure to write your name at the top of the answer sheet and hand it in. These will be the answers you are
graded on. Take the rest of the exam packet with you for use in exam corrections.
1. Two point particles are arranged as shown in the figure below. Particle 1 has charge q1 = +13 µC and
sits at the the origin. Particle 2 has charge q2 = −13 µC and sits at the point (0,2 meters). The net electric
field at the point P at (1.5 m, 1 m) is closest to:
A) 72000ĵ N/C
B) 60000î N/C
C) 40000ĵ N/C
D) −40000ĵ N/C
E) 0 N/C
2. A point particle with charge q is placed exactly at the center of a gaussian surface in the form of a cube.
What is the electric flux through one face of the cube?
A) cannot be determined here
B) q0
C) 2q0
D) 4q0
E) 6q0
3. The potential difference between two ends of a 0.5 m long stick that is held parallel to a uniform electric
field is measured to be 137.5 V. The magnitude of the electric field is closest to:
A) 68.8 N/C
B) 137.5 N/C
C) 275.0 N/C
D) 550.0 N/C
E) 0 N/C
4. An air filled parallel plate capacitor has a capacitance of 1 µF. The plate separation is then halved and a
wax dielectric is inserted filling the space between the plates. As a result the capacitor has a capacitance of
4 µF. What is the dielectric constant of the wax?
A) 1.00
B) 2.00
C) 3.00
D) 4.00
E) 0.50
5. In the figure the ideal batteries have emfs E1 = 150 V and E2 = 50 V and the resistances are R1 = 3.0 Ω
and R2 = 2.0 Ω. If the potential at P is defined to be 140 V, what is the potential at Q?
A) 30 V
B) 250 V
C) 190 V
D) 290 V
E) 20 V
6. A uniform magnetic field of magnitude 0.5 T is directed out of the page. An air filled parallel plate
capacitor is placed in the magnetic field to generate a constant electric field perpendicular to the magnetic
as shown below. The spacing between the plates of the capacitor is 0.1 cm. a positive charge q = +2 µC is
sent through the plates with a speed of 2.0 × 105 m/s. If we desire that this charge should go through the
plates without being deflected at all, what should potential across the capacitor, VA − VB be set to?
A) 200 V
B) 100 V
C) 0 V
D) -100 V
E) -200 V
7. At what orientation angle relative to the magnetic field direction does the potential energy of a magnetic
dipole have its largest value?
A) 0◦
B) 45◦
C) 90◦
D) 135◦
E) 180◦
8. In the figure below, two circular arcs have radii a = 15.0 cm and b = 12.0 cm, subtend angle θ = π/6
radians, carry current i = 0.25 A, and share the same center of curvature P. What is the magnitude and
direction of the net magnetic field at P?
A) 1.96 × 10−7 T into the page
B) 2.18 × 10−8 T into the page
C) 0 T
D) 2.18 × 10−8 T out of the page
E) 1.96 × 10−7 T out of the page
9. The figure below shows the cross section of a long cylindrical wire of radius a = 0.1 meters. A 2.0 Amp
current is running in the cylinder uniformly distributed through its cross section out of the page. What is
the current enclosed by the Amperian loop of radius r = 0.075 m?
A) 3.5 A
B) 2.67 A
C) 2. A
D) 1.50 A
E) 1.13 A
10. A long solenoid is 1.5 m long and is made of 1500 turns of wire is shown from above in the figure below. A
current of 22 amps is sent through the solenoid running clockwise as seen from above. What is the magnitude
and direction of the magnetic field inside of the solenoid?
A) 2.933 × 10−6 T into the page
B) 4.15 × 10−2 T out of the page
C) 2.76 × 10−2 T into the page
D) 2.76 × 10−2 T out of the page
E) 4.15 × 10−2 T into the page
11. A square wire loop with a side length of 25 cm is perpendicular to a magnetic field. The magnitude of the
field is changing in time as B = 0.25 + 0.45t where B is in Tesla and t is in seconds. What is the magnitude
of the emf induced in the loop at time t = 2.0 s?
A) 0.072 V
B) 0.028 V
C) 0.036 V
D) 0.016 V
E) 0. V
12. A 0.25 H inductor is placed in a circuit where the current varies with time as i(t) = −2.5t2 + 3.0t, where
i has units of amperes and t has units of seconds. What is the magnitude and direction of the induced emf
in this inductor at time t = 0.90 s?
A) 0.169 V, opposite the direction of the current
B) 0.189 V, opposite the direction of the current
C) 0.189 V, in the same direction as the current
D) 0.375 V, opposite the direction of the current
E) 0.375 V, in the same direction as the current
13. The figure shows three circuits with identical ideal batteries, identical resistors, and identical inductors.
Rank the circuits according to the current running through the battery, greatest first, a very, very long time
after the switch is closed.
A) 3, 2, 1
B) 2, 3, 1
C) 1, 3, 2
D) 2 and 3 tie, then 1
E) all 3 tie
Name:
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