TEXT FORM - A - UCF Physics

FINAL EXAM – PHY2049, Spring 2013
Instructor: Enrique del Barco
IMPORTANT:
TEXT FORM - A
1) Write your name and mark your UCF-ID in the scantron
2) Select the proper text form, A or B, on the scantron (see upper right corner of this page)
3) Mark only one answer for each the 60 multiple choice questions below
4) You only need to give me the scantron back (nothing else)
5) e = -1.6×10 -19 C; Electron and proton masses m e = 9.11×10 -31 kg and m p = 1.7×10 -27 kg
MULTIPLE CHOICE QUESTIONS (equal weight):
Q1. Which one of the following statements best explains why tiny bits of paper are attracted to a charged
rubber rod?
A) Paper is naturally a positive material.
B) Paper is naturally a negative material.
C) The paper becomes electrically polarized by induction.
D) Rubber and paper always attract each other.
E) The paper acquires a net positive charge by induction.
Q2. A conducting sphere has a net charge of –6.4 × 10 –17 C. What is the approximate number of excess
electrons on the sphere?
A) 100
B) 200
C) 300
D) 400
E) 500
Q3. Four point charges, each of the same magnitude, with varying signs are arranged at the corners of a
square as shown. Which of the arrows labeled A, B, C, and D gives the correct
direction of the net force that acts on the charge at the upper right corner?
A) A
B) B
C) C
D) D
E) The net force on that charge is zero.
Q4. Which one of the following statements is true concerning the strength of the electric field between
two oppositely charged parallel plates?
A) It is zero midway between the plates.
B) It is a maximum midway between the plates.
C) It is a maximum near the positively charged plate.
D) It is a maximum near the negatively charged plate.
E) It is constant between the plates except near the edges.
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Q5. A small sphere of mass 2.5 × 10 –5 kg carries a total charge of 6.0 × 10 –8 C. The sphere hangs from a
silk thread between two large parallel conducting plates. The excess charge on each plate is equal in
magnitude, but opposite in sign. If the thread makes an angle of 30° with the
positive plate as shown, what is the magnitude of the charge density on each plate?
A) 2.5 × 10 –9 C/m 2
B) 5.2 × 10 –9 C/m 2
C) 1.0 × 10 –9 C/m 2
D) 2.1 × 10 –8 C/m 2
E) 4.2 × 10 –8 C/m 2
Q6. What is the magnitude and direction of the electric force on a –3.0 µC charge at a point where the
electric field is 2800 N/C and is directed along the +y axis.
A) 0.018 N, –y direction
B) 0.012 N, +y direction
C) 0.0084 N, –y direction
D) 0.0056 N, +y direction
E) 0.022 N, +x direction
Q7. A cubical Gaussian surface is placed in a uniform electric field as shown in the figure. The length of
each edge of the cube is 1.0 m. The uniform electric field has a magnitude of 5.0 × 10 8 N/C and passes
through the left and right sides of the cube perpendicular to the surface. What is the total electric flux that
passes through the cubical Gaussian surface?
A) 5.0 × 10 8 Nm 2 /C
B) 3.0 × 10 9 Nm 2 /C
C) 2.5 × 10 6 Nm 2 /C
D) 1.5 × 10 7 Nm 2 /C
E) zero Nm 2 /C
Q8. A total charge of –6.50 µC is uniformly distributed within a sphere that has a radius of 0.150 m.
What is the magnitude and direction of the electric field at 0.300 m from the surface of the sphere?
A) 2.89 × 10 5 N/C, radially inward
B) 6.49 × 10 5 N/C, radially outward
C) 4.69 × 10 5 N/C, radially inward
D) 9.38 × 10 5 N/C, radially outward
E) 1.30 × 10 6 N/C, radially inward
Q9. What is the electric flux passing through a Gaussian surface that surrounds a +0.075 C point charge?
A) 8.5 × 10 9 Nm 2 /C
B) 6.8 × 10 8 Nm 2 /C
C) 1.3 × 10 7 Nm 2 /C
D) 4.9 × 10 6 Nm 2 /C
E) 7.2 × 10 5 Nm 2 /C
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Q10. A circular loop of wire with a diameter of 0.626 m is rotated in a uniform electric field to a position
where the electric flux through the loop is a maximum. At this position, the electric flux is 7.50 × 10 5
Nm 2 /C. Determine the magnitude of the electric field.
A) 8.88 × 10 5 N/C
B) 1.07 × 10 6 N/C
C) 2.44 × 10 6 N/C
D) 4.24 × 10 6 N/C
E) 6.00 × 10 6 N/C
Q11. Complete the following statement: The electron volt is a unit of
A) energy.
B) electric field strength.
C) electric force.
D) electric potential difference.
E) electric power.
Q12. Two positive point charges are separated by a distance R. If the distance between the charges is
reduced to R/2, what happens to the total electric potential energy of the system?
A) The total electric potential energy is doubled.
B) The total electric potential energy remains the same.
C) The total electric potential energy increases by a factor of 4.
D) The total electric potential energy is reduced to one-half of its original value.
E) The total electric potential energy is reduced to one-fourth of its original value.
Q13. Which one of the following statements concerning electrostatic situations is false?
A) E is zero everywhere inside a conductor.
B) Equipotential surfaces are always perpendicular to E.
C) Zero work is needed to move a charge along an equipotential surface.
D) If V is constant throughout a region of space, then E must be zero in that region.
E) No force component acts along the path of a charge as it is moved along an equipotential surface.
Q14. The magnitude of the charge on the plates of an isolated parallel plate capacitor is doubled. Which
one of the following statements is true concerning the capacitance of this parallel-plate system?
A) The capacitance is decreased to one half of its original value.
B) The capacitance is increased to twice its original value.
C) The capacitance remains unchanged.
D) The capacitance depends on the electric field between the plates.
E) The capacitance depends on the potential difference across the plates.
Q15. Which one of the following changes will necessarily increase the capacitance of a capacitor?
A) decreasing the charge on the plates
B) increasing the charge on the plates
C) placing a dielectric between the plates
D) increasing the potential difference between the plates
E) decreasing the potential difference between the plates
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Q16. A capacitor is initially charged to 3 V. It is then connected to a 6 V battery. What is the ratio of
the final to the initial energy stored in the capacitor?
A) 3
B) 5
C) 6
D) 7
E) 9
Q17. The plates of a parallel plate capacitor each have an area of 0.40 m 2 and are separated by a distance
of 0.02 m. They are charged until the potential difference between the plates is 3000 V. The charged
capacitor is then isolated.
Determine the magnitude of the electric field between the capacitor plates.
A) 60 V/m
B) 120 V/m
C) 1.0 × 10 5 V/m
D) 1.5 × 10 5 V/m
E) 3.0 × 10 5 V/m
Q18. Suppose that the charges are rearranged as shown in this figure. Which one of the following
statements is true for this new arrangement?
A) The electric field will be zero, but the electric potential remains unchanged.
B) Both the electric field and the electric potential are zero at P.
C) The electric field will remain unchanged, but the electric potential will be zero.
D) The electric field will remain unchanged, but the electric potential will decrease.
E) Both the electric field and the electric potential will be changed and will be non-zero.
Q19. Which one of the following situations results in a conventional electric current that flows
northward?
A) a beam of protons moves eastward
B) an electric dipole moves southward
C) a beam of electrons moves southward
D) a beam of electrons moves northward
E) a beam of protons moves northward
Q20. Complete the following statement: The electromotive force is
A) the maximum potential difference between the terminals of a battery.
B) the force that accelerates electrons through a wire when a battery is connected to it.
C) the force that accelerates protons through a wire when a battery is connected to it.
D) the maximum capacitance between the terminals of a battery.
E) the maximum electric potential energy stored within a battery.
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Q21. A 3.5-A current is maintained in a simple circuit with a total resistance of 1500 . What net charge
passes through any point in the circuit during a thirty second interval?
A) 100 C
B) 180 C
C) 500 C
D) 600 C
E) 5200 C
Q22. Which one of the following combinations of units is equivalent to the ohm?
A) V/C
B) A/J
C) J/s
D) Js/C 2
E) W/A
Q23. Which one of the following
circuits has the largest resistance?
A) a
B) b
C) c
D) d
E) e
Q24. When a light bulb is connected to a 4.5 V battery, a current of 0.12 A passes through the bulb
filament. What is the resistance of the filament?
A) 440
B) 28
C) 9.3
D) 1.4
E) 38
Q25. Determine the length of a copper wire that has a resistance of 0.172 and cross-sectional area of
7.85 × 10 –5 m 2 . The resistivity of copper is 1.72 × 10 –8 m.
A) 873 m
B) 250 m
C) 78.5 m
D) 785 m
E) 6570 m
Q26. Which one of the following statements concerning resistors in series is true?
A) The voltage across each resistor is the same.
B) The current through each resistor is the same.
C) The power dissipated by each resistor is the same.
D) The rate at which charge flows through each resistor depends on its resistance.
E) The total current through the resistors is the sum of the current through each resistor.
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Q27. A 75-W and 50-W incandescent light bulbs are designed for use with the same voltage. What is the
ratio of the resistance of the 75-W bulb to the resistance of the 50-W bulb?
A) 1.5
B) 0.67
C) 2.3
D) 0.44
E) 3.0
Q28. Three resistors are connected as shown in the figure. The potential difference between points A and
B is 26 V. Through which resistor or resistors the current will be lowest?
A) 3.0 ohms
B) 2.0 ohms
C) 4.0 ohms
D) 2.0 ohms and 4.0 ohms
E) 3.0 ohms and 4.0 ohms
Q29. Which one of the following statements concerning permanent magnets is false?
A) The north pole of a permanent magnet is attracted to a south pole.
B) All permanent magnets are surrounded by a magnetic field.
C) The direction of a magnetic field is indicated by the north pole of a compass.
D) Magnetic field lines outside a permanent magnet originate from the north pole and end on the south pole.
E) When a permanent magnet is cut in half, one piece will be a north pole and one piece will be a south pole.
Q30. Which one of the following statements concerning the magnetic force on a charged particle in a
magnetic field is true?
A) The magnetic force is a maximum if the particle is stationary.
B) The magnetic force is zero if the particle moves perpendicular to the field.
C) The magnetic force is a maximum if the particle moves parallel to the field.
D) The magnetic force acts in the direction of motion for a positively charged particle.
E) The magnetic force depends on the component of the particle's velocity that is perpendicular to the field.
Q31. A proton traveling due west in a region that contains only a magnetic field experiences a vertically
upward force (away from the surface of the earth). What is the direction of the magnetic field?
A) north
B) east
C) south
D) west
E) down
Q32. An electron is moving with a speed of 3.5 × 10 5 m/s when it encounters a magnetic field of 0.60 T.
The direction of the magnetic field makes an angle of 60.0° with respect to the velocity of the electron.
What is the magnitude of the magnetic force on the electron?
A) 4.9 × 10 –13 N
B) 3.2 × 10 –13 N
C) 1.7 × 10 –13 N
D) 3.4 × 10 –14 N
E) 2.9 × 10 –14 N
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Q33. Two particles move through a uniform magnetic field that is directed out of the plane of the page.
The figure shows the paths taken by the two particles as
they move through the field. The particles are not subject
to any other forces or fields. Which one of the following
statements concerning these particles is true?
A) The particles may both be neutral.
B) Particle 1 is positively charged; 2 is negative.
C) Particle 1 is positively charged; 2 is positive.
D) Particle 1 is negatively charged; 2 is negative.
E) Particle 1 is negatively charged; 2 is positive.
Q34. A 0.0150-m wire oriented horizontally between the poles of an electromagnet carries a direct
current of 9.5 A. The angle between the direction of the current and that of the magnetic field is 25.0° as
shown. If the magnetic field strength is 0.845 T, what is the
magnitude and direction of the magnetic force on the wire
between the poles?
A) 1.17 N, upward
B) 0.330 N, downward
C) 0.0509 N, upward
D) 0.120 N, downward
E) 0.495 N, upward
Q35. Which one of the following statements concerning the magnetic field inside (far from the surface) a
long, current-carrying solenoid is true?
A) The magnetic field is zero.
B) The magnetic field is non-zero and nearly uniform.
C) The magnetic field is independent of the number of windings.
D) The magnetic field is independent of the current in the solenoid.
E) The magnetic field varies as 1/r as measured from the solenoid axis.
Q36. A solenoid of length 0.250 m and radius 0.0250 m is comprised of 440 turns of wire. Determine
the magnitude of the magnetic field at the center of the solenoid when it carries a current of 12.0 A.
A) 2.21 × 10 –3 T
B) 4.52 × 10 –3 T
C) 9.05 × 10 –3 T
D) 7.50 × 10 –3 T
E) zero tesla
Q37. A long, straight wire carries a current I. If the magnetic field at a distance d from the wire has
magnitude B, what is the magnitude of the magnetic field at a distance 2d from the wire?
A) B/2
B) B/4
C) 2B
D) 4B
E) 8B
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Q38. A coil of wire carries current I as shown in the figure on the right. If the observer could “see” the
magnetic field inside this arrangement of loops, how would it appear?
A) a
B) b
C) c
D) d
E) e
Q39. A long, straight wire is carrying a current of 5.0 A in the direction shown in the figure. The point P
is 0.040 m from the wire. What is the direction of the
magnetic field at point P due to the current in the wire?
A) to the right of page
B) to the left of the page
C) toward the bottom of the page
D) into the plane of the page
E) out of the plane of the page
Q40. A conducting loop of wire is placed in a magnetic field that is normal to the plane of the loop.
Which one of the following actions will not result in an induced current in the loop?
A) Rotate the loop about an axis that is parallel to the field and passes through the center of the loop.
B) Increase the strength of the magnetic field.
C) Decrease the area of the loop.
D) Decrease the strength of the magnetic field.
E) Rotate the loop about an axis that is perpendicular to the field and passes through the center of the loop.
Q41. A conducting bar moves to the left at a constant speed v on two conducting rails joined at the left as
shown. As a result of the bar moving through a constant magnetic field, a current I is induced in the
indicated direction. Which one of the following directions is that of
the magnetic field?
A) toward the right
B) toward the left
C) parallel to the long axis of the bar
D) into the page
E) out of the page
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Q42. A long, straight wire is in the same plane as a rectangular, conducting loop. The wire carries a
constant current I as shown in the figure. Which one of the following statements is
true if the wire is suddenly moved toward the loop?
A) There will be no induced emf and no induced current.
B) There will be an induced emf, but no induced current.
C) There will be an induced current that is clockwise around the loop.
D) There will be an induced current that is counterclockwise around the loop.
E) There will be an induced electric field that is clockwise around the loop.
Q43. Two conducting loops carry equal currents I in the same direction as shown in the figure. If the
current in the upper loop suddenly drops to zero, what will happen to the current in
the lower loop according to Lenz's law?
A) The current in the lower loop will decrease.
B) The current in the lower loop will increase.
C) The current in the lower loop will not change.
D) The current in the lower loop will also drop to zero.
E) The current in the lower loop will reverse its direction.
Q44. The figure shows a circular, conducting loop that is connected to a 5.0-V battery and a switch S.
Immediately after the switch S is closed, the current through the loop changes at a rate of 15 A/s and the
emf induced in the loop has a magnitude of 5.0 V. Determine the selfinductance
of the coil.
A) 0.33 H
B) 0.60 H
C) 1.5 H
D) 3.0 H
E) 5.0 H
Q45. Two coils share a common axis as shown in the figure. The mutual inductance of this pair of coils
is 6.0 mH. If the current in coil 1 is changing at the rate of 3.5
A/s, what is the magnitude of the emf generated in coil 2?
A) 5.8 × 10 –4 V
B) 1.7 × 10 –3 V
C) 3.5 × 10 –3 V
D) 1.5 × 10 –2 V
E) 2.1 × 10 –2 V
Q46. An ac voltage source that has a frequency f is connected across the terminals of a capacitor. Which
one of the following statements correctly indicates the effect on the capacitive reactance when the
frequency is increased to 4f?
A) The capacitive reactance increases by a factor of four.
B) The capacitive reactance increases by a factor of eight.
C) The capacitive reactance is unchanged.
D) The capacitive reactance decreases by a factor of eight.
E) The capacitive reactance decreases by a factor of four.
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Q47. Three 4.0-µF capacitors are connected in parallel across the terminals of a 60.0-Hz generator.
What is the capacitive reactance of the circuit?
A) 39
B) 110
C) 330
D) 660
E) 1.0 × 10 3
Q48. Which one of the following
phasor models correctly represents a
circuit comprised of only an inductor
and an ac generator?
A) a
B) b
C) c
D) d
E) e
Q49. Complete the following statement: When the current in an oscillating LC circuit is zero,
A) the charge on the capacitor is zero.
B) the energy in the electric field is maximum.
C) the energy in the magnetic field is a maximum.
D) the charge is moving through the inductor.
E) the energy is equally shared between the electric and magnetic fields.
Q50. Use the information given in the figure for the series RCL circuit to determine its total impedance.
A) 300
B) 500
C) 1500
D) 1700
E) 1900
Take care, my wonderful engineers. And by the way,
if any of you ends designing planes, please make
wider coaches… (I keep requesting this every
semester but it has not worked out yet)
Enrique
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