TENNESSEE STATE UNIVERSITY
PHYSICS 2120
FINAL EXAMINATION, SU 2008
Name__________________ID#_______________Date___________Score__________
DIRECTIONS: Each of the problems below is followed by a list of possible answers. Select the best
possible answer, and shade in the corresponding alphabet on the sheet provided. Each problem is
worth ten (10) points for a total of 300 points. Other instructions will be given in the EXAM HALL, if
necessary.
1.
Determine the current in the 10-V emf.
a. 2.3 A b. 2.7 A c.
2.
1.3 A
d. 0.30 A
e.
2.5 A
In order for two objects to have the same temperature, they must
a.
be in thermal equilibrium. b.
be in thermal contact with each other.
c.
have the same relative “hotness” or “coldness” when touched.
d. have all of the properties listed above. e. have only properties (b) and (c) above.
3.
Two thermometers are calibrated, one in degrees Celsius and the other in degrees Fahrenheit. At
what temperature (in kelvins) do their readings measure the same temperature?
a.
4.
5.
218.15
b. 233.15
c. 273.15
d. 40.15 e. 0
A 5.0-nC point charge is embedded at the center of a nonconducting sphere (radius = 2.0
cm) which has a charge of –8.0 nC distributed uniformly throughout its volume. What is
the magnitude of the electric field at a point that is 1.0 cm from the center of the sphere?
5
4
5
5
5
a. 1.8  10 N/C b. 9.0  10 N/C c. 3.6  10 N/C d. 2.7  10 N/C e. 7.2  10 N/C
A gallon container is filled with gasoline. How many gallons are lost if the temperature increases
–1
by 25F? (The volume expansion of gasoline is 9.6 104 (C) .) (Neglect the change in
volume of the container.)
6.
–2
–2
–2
–2
–2
a.
2.4  10
b. 1.3  10
c. 3.6  10
d. 4.8  10
e. 9.6  10
Which of the following is not a possible thermometric property of a body?
7.
a. The change in length of a solid. b. the change in volume of a gas at constant pressure.
c.
The change in pressure of a gas at constant volume. d. The change in weight at constant
pressure and volume.
e. The change in electrical resistance of a conductor.
The electric field in the region defined by the y-z plane and the positive x axis is given by E  ax,
where a is a constant. (There is no field for negative values of x.) As x increases in magnitude, relative to
V  0 at the origin, the electric potential in the region defined above is: a. a decreasing function
proportional to  x2 . b. a decreasing function proportional to  x . c. constant. d. an
increasing function proportional to  x . e. an increasing function proportional to  x2 .
8.
The area of a rectangular loop of wire is 3.4 × 10 -3 m2. The loop is placed in a magnetic field that
changes from 0.20 T to 1.2 T in 1.6 s. The plane of the loop is perpendicular to the direction of the
magnetic field. What is the magnitude of the induced emf in that loop?
A) 2.8 × 10-3 V B) 2.1 × 10-3 V C) 0 V
D) 1.8 × 10-3 V
9.
Which statement below is NOT an assumption made in the molecular model of an ideal gas?
a. The average separation between molecules is large compared with the dimensions of the
molecules. b. The molecules undergo inelastic collisions with one another.
c. The forces between molecules are short range. d. The molecules obey Newton’s laws of
motion. e. Any molecule can move in any direction with equal probability.
10.
The theorem of equipartition of energy states that the energy each degree of freedom contributes
to each molecule in the system (an ideal gas) is
a.
1
1
3
1 2
3
mv . b. kB T . c. kB T . d. mv 2 . e. kB T .
3
2
2
2
2
11. Calculate the change in entropy of 250 g of water heated slowly from 20 oC to 80 oC.
a) 300 J/K
b) 253 J/K
c) 195 J/K
d) 98 J/K
12. Two small beads having positive charges 3q and q are fixed at the opposite ends of a horizontal
insulating rod extending from the origin to the point x=d. A third small charged bead is free to slide on the
rod. At what position is the third bead in equilibrium?
a) 0.634 d
b) 6.34 d
c) 0.532 d
d) 5.32 d
13. A heat engine absorbs 360 J of energy and performs 25 J of work in each cycle. Determine the
efficiency of the engine:
a) 6.94%
b) 0.0694%
c) 7.8%
d) 0.078%
14. How much energy is required to convert 1.0 g of ice at –30oC to steam at 120 oC?
Lf=3.33x105 J/kg and Lv = 2.26x106 J/kg
a) 62.7 J
b) 419 J
c) 2.26x103 J
d) 3.11x103 J
15. Three charges are placed as follows along the x and y axes of an xy-coordinate system: q1 = 2.00 µC at
x1 = 0 m, q2 = 4.00 µC at x2 = 3.00 m, and q3 = 6.00 µC at y = 4.00 m. What is the electric potential energy
of this system of charges?
A) -94.2 mJ
B) 94.2 mJ
C) 0 J D) 90.0 mJ
16. The work done in moving a positive charge against an electric field does not depend on the path chosen
in moving the charge in that field. Based on the statement, what kind of force field is the electrostatic field?
A) discrete
B) quantized
C) polarized
D) conservative
17. An electron is initially at rest. It is accelerated through a potential difference of 400 V. What is the
kinetic energy of this electron?
A) 6.4 × 10-17 J B) 4.0 × 102 J
C) 0 J D) 6400 J
18. An 800 V/m electric field is directed along the +x-axis. If the potential at x = 0 m is 2000 V, what is the
potential at x = 2 m?
A) 200 V
B) 400 V
C) 600 V
D) 800 V
19. When a negative charge is released and moves along an electric field line, it moves to a position of
a. lower potential and lower potential energy. b. lower potential and higher potential energy.
c. higher potential and lower potential energy. d. higher potential and higher potential energy.
e. decreasing magnitude of the electric field.
20. A parallel plate capacitor with plate separation of 4.0 cm has a plate area of 4.0 × 10 -2 m2. What is the
capacitance of this capacitor if a dielectric material with a dielectric constant of 2.4 is placed between the
plates?
A) 3.7 × 10-12 F B) 3.7 × 10-14 F C) 21 × 10-14 F
D) 21 × 10-12 F
21. A 4.0-Ω resistor is connected in parallel with a 12-Ω resistor and both of these are connected to a DC
power supply with voltage V as shown in Figure above. If the total current in this circuit is 2.0 A, what is
the current through the 4.0-Ω resistor?
A) 2.0 A
B) 0.5 A
C) 3.0 A
D) 1.5 A
22. Three capacitors are connected as shown in Figure above. What is the equivalent capacitance between
points A and B?
A) 1.7 µF
B) 7.1 µF
C) 12 µF
D) 8.0 µF
23. A 5.0 mF capacitor is connected in series with a 3.0 kΩ resistor across a 20-V DC source and an open
switch. If the switch is closed at t = 0 s, what is the charge on the capacitor at t = 9 ms?
A) 0 C B) 37% of the minimum charge C) 45% of the maximum charge* D) 96% of the maximum charge
24. Figure above shows four Gaussian surfaces surrounding a distribution of charges. The Gaussian
surface (surfaces) that has (have) electric flux of +q/εo through it (them) is (are)
A) a.
B) b.
C) b and d.
D) c.
25)
A conducting rod whose length is 25 cm is placed on a U-shaped metal wire that has a resistance R of 8 Ω
as shown in Figure above. The wire and the rod are in the plane of the paper. A constant magnetic field of
strength 0.4 T is applied perpendicular and into the paper. An applied force moves the rod to the right with
a constant speed of 6 m/s. What is the magnitude of the induced emf in the wire?
A) 0.2 V
B) 0.4 V
C) 0.5 V
D) 0.6 V
26) A straight wire 20 cm long, carrying a current of 4 A, is in a uniform magnetic field of 0.6 T. What is
the force on the wire when it is at an angle of 30° with respect to the field?
A) 0.2 N
B) 0.3 N
C) 0.4 N
D) 0.5 N
27) A particle (q = –4.0 µC, m = 5.0 mg) moves in a uniform magnetic field with a velocity having
a magnitude of 2.0 km/s and a direction that is 50 away from that of the magnetic field.
2
The particle is observed to have an acceleration with a magnitude of 5.8 m/s . What is
the magnitude of the magnetic field?
a.
5.3 mT
b. 4.9 mT
c. 5.1 mT
d. 4.7 mT
e.
3.6 mT
28) A current loop is oriented in three different positions relative to a uniform magnetic field. In position 1
the plane of the loop is perpendicular to the field lines. In position 2 and 3 the plane of the loop is parallel
to the field as shown. The torque on the loop is maximum in
a. position 1. b. position 2. c. position 3
d. positions 2 and 3. e.
all three positions.
29) Each of two parallel wires separated by 8.0 mm carries a 20-A current. These two currents are
oppositely directed. Determine the magnitude of the magnetic field at a point that is 5.0
mm from each of the wires.
a.
2.0 mT
b. 1.6 mT
c. 1.3 mT
d. 1.8 mT
e. 1.0 mT
30) Most telephone cables are made of copper wire of either 24 or 26 gauge. If the resistance of
24-gauge wire is 137 /mile and the resistance of 26-gauge wire is 220 /mile, what is
the ratio of the diameter of 24-gauge wire to that of 26-gauge wire?
a.
1.6 b. 1.3
c. 0.62 d. 0.79
e.
0.88