Download practice questions for exam 3 phys 202 1

Physics 202
Spring 2010
Practice Questions for Exam 3
Note: Answer key is at end
1. For the two solenoids above, if l = 50 cm, N1 = N2 = 200 turns and r1 = 5 cm and r2 =
10 cm, the mutual inductance of the two solenoids is
A) 1.58 mH
B) 0.790 mH
C) 3.20 mH
D) 6.31 mH
E) None of these is correct.
2. A region of space contains a magnetic field of 500 G and an electric field of 3 × 106
N/C. The magnetic energy density in a cubical box of side  = 20 cm in this region
is
A) 550 J/m3
B) 670 J/m3
C) 864 J/m3
D) 995 J/m3
E) None of these is correct.
3. An LR circuit has a resistance R = 25 Ω, an inductance L = 5.4 mH, and a battery of
EMF = 9.0 V. How much energy is stored in the inductance of this circuit when a
steady current is achieved?
A) zero
B) 0.35 J
C) 0.35 mJ
D) 0.70 mJ
E) 0.97 mJ
1 4. What is the time constant of an RL circuit with a resistance R = 25 Ω and an
inductance L = 5.4 mH?
A) 7.4 s
B) 4.6 s
C) 0.14 s
D) 0.22 ms
E) 1.5 ms
5. An open switch in an RL circuit is closed at time t = 0, as shown. The curve that best
illustrates the variation of current with time is
A) 1
B) 2
C) 3
D) 4
E) 5
6. The growth of current in the inductive circuit in the inset diagram is represented by the
curve in the graph. The broken line is tangent to the curve at the origin. The time
constant of the circuit is approximately
A) 3.0 ms
B) 2/R ms
C) 0.40 ms
D) 4.0 ms
E) 2.0 ms
2 7. The current in an RL circuit is zero at time t = 0 and increases to half its final value in
6.0 s. The time constant of this circuit is approximately
A) 6.0 s
B) 12 s
C) 8.7 s
D) 3.0 s
E) 9.8 s
8. In this circuit, the current I through the battery is approximately
A) 1.7 A
B) 4.4 A
C) 0.36 A
D) 0.60 A
E) 3.4 A
9. A 1.2-µF capacitor in a flash camera is charged by a 1.5-V battery. When the camera
flashes, this capacitor is discharged through a resistor. The time constant of the
circuit is 10 ms. What is the value of the resistance?
A) 8.0 × 10–2 Ω
B) 0.12 Ω
C) 12 kΩ
D) 8.3 kΩ
E) 3.1 kΩ
10. A 20-µF capacitor is charged to 200 V and is then connected across a 1000-Ω
resistor. What is the initial charge on the capacitor?
A) 10 mC
B) 5.6 mC
C) 4.0 mC
D) 8.0 mC
E) 2.0 mC
3 11. A 20-µF capacitor is charged to 200 V and is then connected across a 1000-Ω
resistor. The time constant for this circuit is approximately
A) 20 ms
B) 40 ms
C) 10 ms
D) 30 ms
E) 15 ms
12. A 20-µF capacitor is charged to 200 V and is then connected across a 1000-Ω
resistor. The amount of charge on the capacitor after 10 ms is approximately
A) 14 mC
B) 2.4 mC
C) 0.80 mC
D) 1.6 mC
E) 3.2 mC
13. A 0.120-µF capacitor, initially uncharged, is connected in series with a 10.0-kΩ
resistor and a 12.0-V battery of negligible internal resistance. The charge on the
capacitor after a very long time is approximately
A) 28.8 µC
B) 14.4 µC
C) 144 µC
D) 2.88 µC
E) 1.44 µC
14. An uncharged capacitor and a resistor are connected in series to a battery as shown.
If ε = 15 V, C = 20 µF, and R = 4.0 × 105 Ω, the time constant of the circuit is
approximately
A) 10 s
B) 8.0 s
C) 18 s
D) 4.0 s
E) 2.5 s
4 15. An uncharged capacitor and a resistor are connected in series to a battery as shown.
If ε = 15 V, C = 20 µF, and R = 4.0 × 105 Ω, the current as a function of time for this
circuit is
A) I(t) = 37.5 e0.250t µA
B) I(t) = 150 e–0.250t µA
C) I(t) = 37.5 e–0.250t µA
D) I(t) = 37.5 e–0.125t µA
E) I(t) = 300 e–0.125t µA
16. Lea charges a capacitor and then discharges it through a resistor. She notices that,
after three time constants, the voltage across the capacitor has decreased to _____ of
its value just prior to the initiation of the discharge.
A) 0.368
B) 0.135
C) 0.0498
D) 0.0183
E) 0.00674
17. How much does the maximum EMF produced by a generator (a rotating coil) change
if the period of rotation is doubled?
A) it is the same
B) it is doubled
C) it is quadrupled
D) it is halved
E) it is quartered
18. A motor sometimes burns out when its load is suddenly increased because the
resulting sudden decrease in its rotational frequency causes
A) an increased back EMF and an increased current flow.
B) a decreased back EMF and a decreased current flow.
C) a decreased back EMF and zero current flow.
D) an increased back EMF and a decreased current flow.
E) a decreased back EMF and an increased current flow.
5 19. The resistance of the armature windings of DC motor is 5 Ω. The motor is connected
to a 120 V line. When the motor is spinning at full speed, it draws a current of 4 A.
The back EMF at full speed is
A) 20 V
B) 100 V
C) 120 V
D) 40 V
E) 80 V
20. A 200-turn coil rotates in a magnetic field of magnitude 0.25 T at a frequency of 60
Hz. The area of the coil is 5.0 cm2. What is the maximum EMF in the coil?
A) 1.5 V
B) 4.5 V
C) 9.0 V
D) 9.4 V
E) 24 V
21. A simple generator consists of a single rectangular loop of wire rotating between two
magnetic pole faces as shown. Which curve in the graph correctly represents the
EMF ε as a function of the angle between the normal to the plane of the coil and the
direction of the magnetic field?
A) 1
B) 2
C) 3
D) 4
E) None of these is correct.
6 22. A square coil with 12 turns and side 5 cm is rotated in a uniform magnetic field of
1.2 T at an angular frequency of 90 radians per second. What is the maximum
voltage induced in the coil?
A) 10 V
B) 3.2 V
C) 0.51 V
D) 0.27 V
E) none of the above
23. A circular coil with 20 turns and radius 5 cm is rotated in a uniform magnetic field of
3.2 T. If the maximum voltage induced in the coil is 5 V, calculate the number of
rotations of the coil per minute.
A) 600 revs per minute
B) 15 revs per minute
C) 5 revs per minute
D) 95 revs per minute
E) 200 revs per minute
24. If you were to plug a 1200-W heater and a 600-W toaster into a 110-V electrical
outlet, what total rms current would these two appliances draw if the wiring is
parallel?
A) 5.45 A
B) 10.9 A
C) 11.6 A
D) 16.4 A
E) 23.1 A
25. Two heaters are plugged into the same 120-V AC outlet. If one heater is rated at
1100 W, then what can be the maximum rating of the second heater in order not to
exceed the 20 A trip rating on the circuit?
A) 1100 W
B) 1300 W
C) 1200 W
D) 2400 W
E) 920 W
7 26. If you connect a 12-V rms AC power supply that operates at 5.0 kHz to a 20-µF
capacitor, what is the rms current in the circuit? (neglect any resistance)
A) 1.2 A
B) 7.5 A
C) 19 A
D) 8.4 A
E) 11 A
27. An inductor with inductance L = 10 mH is connected to a power supply which
provides a current I = 5 mA sin ωt. The maximum back EMF is
A) 5 mV
B) 10 mV
C) 25 µV
D) 50 µV
E) 0 V
28. At what frequency would the reactance of a 100-pF capacitor be 1000 Ω?
A) 3.18 MHz
B) 15.9 MHz
C) 1.59 MHz
D) 3.98 MHz
E) 2.54 Mhz
29. At what frequency would the reactance of a 1.0-mH inductor be twice that of a 10-µF
capacitor?
A) 10 kHz
B) 3.2 kHz
C) 2.2 kHz
D) 1.6 kHz
E) 1.1 kHz
30. An inductor is placed across an AC generator that has a maximum EMF of 170 V.
For a frequency of 3000 Hz, the rms current through the inductor is 5.0 A. Find the
value of the inductor.
A) 8.0 × 10–3 H
B) 9.2 × 10–4 H
C) 1.8 × 10–3 H
D) 1.3 × 10–3 H
E) 5.6 × 10–3 H
8 31. A 5-µF capacitor is charged to 30 V and is then connected across a 10-µH inductor.
The maximum value of the current in this circuit is
A) 1.41 A
B) 2.25 A
C) 8.73 A
D) 15.4 A
E) 21.2 A
32. The battery has a voltage V = 6 V, the inductance of the inductor L = 12 mH and the
capacitance of the capacitor C = 8 µF. Assume that the inductor and the wires have
zero resistance.
The switch S was at position a for a long time when it is switched to b. What is the
charge on the capacitor at t = 0 s?
A) 0.75 µC
B) 1.33 µC
C) 48 µC
D) 72 µC
E) zero
33. The battery has a voltage V = 6 V, the inductance of the inductor L = 12 mH and the
capacitance of the capacitor C = 8 µF. Assume that the inductor and the wires have
zero resistance.
The switch S was at position a for a long time when it is switched to b. What is the
charge on the capacitor at t = 0.487 ms?
A) 0.75 µC
B) 1.33 µC
C) 48 µC
D) 72 µC
E) zero
9 34. A 10-mH inductor has a resistance of 10 Ω. Its impedance in an AC circuit is
A) 10 Ω
B) 14 Ω
C) 0.10 kΩ
D) 5.0 Ω
E) impossible to tell from the given information.
35. You have a 30-µH inductor and a 50-µF capacitor with which you form a parallel,
resonant circuit. The frequency of this circuit will be
A) 4.11 kHz
B) 13.7 kHz
C) 25.8 kHz
D) 31.7 kHz
E) 39.1 kHz
36. The approximate resonant frequency of the circuit shown is
A) 1.5 kHz
B) 0.25 kHz
C) 2.4 MHz
D) 25 kHz
E) None of these is correct.
37. A series RLC circuit is driven by a 1.0-kHz oscillator. The circuit parameters are L =
5.0 mH, C = 4.0 µF, R = 10 Ω. If you adjust the frequency of the oscillator so that it
is at the resonance frequency of the RLC circuit, and if it supplies 3.0 V rms, what is
the rms current in the circuit?
A) 0.23 A
B) 0.36 A
C) 0.21 A
D) 0.30 A
E) 0.42 A
10 38. A series RLC circuit is driven by a 1.0-kHz oscillator. The circuit parameters are
Vrms = 12 V, L = 5.0 mH, C = 4.0 µF, and R = 10 Ω. Under steady-state conditions,
the rms potential difference across the resistor will be
A) 5.13 V
B) 9.19 V
C) 12.3 V
D) 14.7 V
E) 18.8 V
39. You connect a 100-Ω resistor, a 800-mH inductor, and a 10.0-µF capacitor in series
across a 60.0-Hz, 120-V (peak) source. The impedance of your circuit is
approximately
A) 377 Ω
B) 302 Ω
C) 265 Ω
D) 100 Ω
E) 107 Ω
40. You connect a 250-Ω resistor, a 1.20-mH inductor, and a 1.80-µF capacitor in series
across a 60.0-Hz, 120-V (peak) source. The approximate impedance of your circuit
is
A) 1.49 kΩ
B) 1.47 kΩ
C) 0.452 Ω
D) 250 Ω
E) None of these is correct.
41. You connect a 250-Ω resistor, a 1.20-mH inductor, and a 1.80-µF capacitor in series
across a 60.0-Hz, 120-V (peak) source. When you connect a voltmeter across the
resistor in this circuit, the meter reads approximately
A) 25.7 mV
B) 83.6 V
C) 120 V
D) 14.2 V
E) 84.9 V
11 42. An AC power supply, V = 20 V sin ωt where ω = 200 rad/s is connect to an inductor L
= 180 mH and a capacitor C = 25 µF. XL = 36 ohms, XC = 200 ohms, Z = 43.9
ohms
What is the peak current flow out of the AC power supply?
A) 85 mA
B) 0.56 A
C) 0.46 A
D) 0.10 A
E) None of these is correct.
43. The graph shows the average power delivered to an oscillating system as a function
of the driving frequency.
According to these data
A) the resonant frequency is greater than ωo.
B) the system corresponding to curve 1 has the largest quality factor.
C) the system corresponding to curve 4 has the largest quality factor.
D) the resonant frequency is less than ωo.
E) None of these is correct.
12 44. The graph shows the average power delivered to an oscillating system as a function
of the driving frequency.
According to these data, the damping is greatest for system(s)
A) 1
B) 2
C) 3
D) 4
E) 1 and 2
45. When a body capable of oscillating is acted on by a periodic series of impulses
having a frequency equal to one of the natural frequencies of oscillation of the body,
the body is set in vibration with relatively large amplitude. This phenomenon is
known as
A) beats.
B) harmonics.
C) overtones.
D) resonance.
E) pressure amplitude.
13 46. Near resonance, if the damping is small (large Q), the oscillator
A) absorbs less energy from the driving force than it does at other frequencies.
B) absorbs more energy from the driving force than it does at other frequencies.
C) absorbs the same amount of energy from the driving force than it does at other
frequencies.
D) moves with a small amplitude.
E) is described by none of these
47. A parallel-plate capacitor has closely spaced circular plates of radius R = 2.00 cm.
Charge is flowing onto the positive plate at the rate I = dQ/dt = 1.36 A. The
magnetic field at a distance r = 2.00 cm from the axis of the plates is approximately
A) 136 mT
B) 256 mT
C) 16.5 mT
D) 457 mT
E) 88.3 mT
48. An AC voltage is applied across a capacitor. Which figure best represents the
magnetic field between the capacitor?
A) 1
B) 2
C) 3
D) 4
E) 5
14 49. An AC voltage, V = 20 V sin (1000 rad/s t) is applied across a capacitor of
capacitance C = 40 µF. The capacitor is made of two circular plate each of radius
r = 5 cm. What is the peak magnetic field at the circumference of the capacitor?
A) 1.2 µT
B) 1.6.2 µT
C) 3.2 µT
D) 72 µT
E) None of these is correct.
50. Which of the following statements contradicts one of Maxwell's equations?
A) A changing magnetic field produces an electric field.
B) The net magnetic flux through a closed surface depends on the current inside.
C) A changing electric field produces a magnetic field.
D) The net electric flux through a closed surface depends on the charge inside.
E) None of these statements contradict any of Maxwell's equations.
51. Which of the following statements is true?
A) A changing electric field induces a magnetic field.
B) A changing magnetic field induces an electric field.
C) Maxwell's equations predict the speed of light.
D) Maxwell's equations predict that light is made up of oscillating electric and magnetic
waves.
E) All the above statements are true.
52. If the existence of magnetic monopoles should ever be confirmed, which of the
following equations would have to be altered?
A)
B)
C)
D)
E) all would still apply
15 53. Which of the following statements is false?
A) isolated electric charges exist
B) Electric field lines diverge from positive charges and converge on negative charges.
C) The flux of the magnetic field vector is zero through any closed surface.
D) isolated magnetic poles exist
E) changing electric fields induce changing magnetic fields
54. Which of the following functions satisfy the one-dimensional wave equation?
A) y(x, t) = y0 cos(kx – ωt)
B) y(x, t) = y0 sin(kx – ωt)
C) y(x, t) = y0 sin(kx – ωt) + B cos(kx – ωt)
D) y(x, t) = y0 (sin kx) · B(cos ωt)
E) All of these functions satisfy the one-dimensional wave equation.
55. Which of the following statements is true?
A) Maxwell's equations apply only to fields that are constant in time.
B) Electromagnetic waves are longitudinal waves.
C) The electric and magnetic fields are out of phase in an electromagnetic wave.
D) The electric- and magnetic-field vectors and are equal in magnitude in an
electromagnetic wave.
E) None of these statements is true.
56. The electric field of an electro-magnetic wave is given by Ey = 25 sin(2.4 × 106 π (x –
3.0 × 108t)). What is the frequency of the wave?
A) 4.8 × 107 s–1
B) 3.6 × 1014 s–1
C) 1.2 × 106 s–1
D) 2.3 × 1015 s–1
E) none of the above
57. A beam of light is propagating in the x direction. The electric-field vector
A) can oscillate in any arbitrary direction in space.
B) must oscillate in the z direction.
C) must oscillate in the yz plane.
D) must oscillate in the x direction.
E) must have a steady component in the x direction.
16 58. The wavelength of a 150-MHz television signal is approximately
A) 1.0 m
B) 1.5 m
C) 2.0 m
D) 2.0 cm
E) 50 cm
59. The frequency range for FM broadcasts is from 87.9 – 107.9 MHz in the U.S. In
terms of wavelengths, the range corresponds to
A) 87.9 – 107.9 m
B) 2.78 – 3.41 m
C) 83.3 – 102.3 m
D) 12.4 – 19.5 m
E) None of these is correct.
60. Which of the following does not result in the production of electromagnetic waves?
A) charges moving at a constant velocity
B) charges that are accelerating or decelerating
C) charges moving around in a circle
D) electrons that make a transition from one atomic level to another
E) an oscillating electric current
61. You are using an antenna consisting of a single loop of wire of radius 15.0 cm to
detect electromagnetic waves for which Erms = 0.200 V/m. If the wave frequency is
600 Hz, the rms value of the emf induced in the loop is approximately
A) 32.1 nV
B) 84.3 nV
C) 66.7 nV
D) 178 nV
E) 643 nV
17 62. The left part of the figure shows an dipole oscillating in a sinusoidal function. Which
of the curves best represents the electric field along the axis of the dipole?
A) 1 – sinusoidal wave in the plane of the dipole
B) 2 – sinusoidal wave perpendicular to the plane of the dipole
C) 3 – circular wave perpendicular to the plane of the dipole
D) 4 – circular wave in the plane of the dipole
E) None of these is correct.
63. A 60-W light bulb emits spherical electromagnetic waves uniformly in all directions.
If 50% of the power input to such a light bulb is emitted as electromagnetic
radiation, what is the radiation intensity at a distance of 2.00 m from the light bulb?
A) 15 W/m2
B) 4.8 W/m2
C) 2.4 W/m2
D) 0.60 W/m2
E) 1.2 W/m2
64. A 60-W light bulb emits spherical electromagnetic waves uniformly in all directions.
If 50% of the power input to such a light bulb is emitted as electromagnetic
radiation, what is the radiation pressure at a distance of 2.0 m from the light bulb?
A) 50 nPa
B) 2.0 nPa
C) 8.0 nPa
D) 16 nPa
E) 4.0 nPa
65. The Sun radiates about 3.83 × 1026 W of power. How large should a perfectly
reflecting solar sail be on a space ship of mass 50 kg to provide an acceleration of
10-4 m/s2 at the Earth's orbit? The radius of Earth's orbit is 1.50 × 1011 m.
A) 550 m2
B) 625 m2
C) 1100 m2
D) 2500 m2
E) None of these is correct.
18 66. The rms value of the electric field in an electromagnetic wave is Erms = 200 V/m. The
intensity of this wave is approximately
A) 53.1 W/m2
B) 106 W/m2
C) 1.59 × 1010 W/m2
D) 3.18 × 1010 W/m2
E) 1.70 kW/m2
67. The rms value of the electric field in an electromagnetic wave is Erms = 600 V/m.
The average energy density of this wave is approximately
A) 0.796 µJ/m3
B) 1.59 µJ/m3
C) 3.18 µJ/m3
D) 6.78 µJ/m3
E) 5.21 µJ/m3
68. Charge is flowing onto one plate of a parallel-plate capacitor and off the other plate
at a rate of 5.00 A. The rate at which the electric field between the plates is
changing is approximately
A) 5.65 × 1011 N · m2/(C · s)
B) 11.3 × 1011 N · m2/(C · s)
C) 2.45 × 1011 N · m2/(C · s)
D) 12.4 × 1011 N · m2/(C · s)
E) 1.76 × 1011 N · m2/(C · s)
69. The electric field of an electro-magnetic wave is given by Ey = 25 sin(2.4 × 106 π (x –
3.0 × 108t)). What is the wavelength of the wave?
A) 4.8 × 107 m
B) 2.1 × 10–8 m
C) 2.1 × 10–7 m
D) 8.3 × 10–7 m
E) 7.5 × 10–6 m
19 70. The intensity of a laser beam is 450 W/m2. What is the rms value of the electric field
of this laser beam? (The permittivity of free space ε0 = 8.85 × 10–12 C2/N · m2 and
the permeability of free space µ0 = 4π × 10–7 N/A2.)
A) 1.7 × 105 V/m
B) 5.8 × 102 V/m
C) 3.4 × 105 V/m
D) 4.1 × 102 V/m
E) 1.3 × 103 V/m
71. A 60-W light bulb emits spherical electromagnetic waves uniformly in all directions.
If 50% of the power input to such a light bulb is emitted as electromagnetic
radiation, what is the maximum value of the electric field at a distance of 2.0 m
from the light bulb?
A) 43 V/m
B) 0.11 mV/m
C) 21 V/m
D) 60 V/m
E) 30 V/m
72. There are many different regions to the electromagnetic spectrum. These include, (a)
visible light, (b) gamma-rays, (c) infra-red, (d) micro-waves, (e) radio-waves, (f)
ultra-violet, and (g) X-rays. Put them in order of increasing wavelength, starting
with the shortest wavelength first.
A) bgdafge
B) bgfadce
C) bgafcde
D) bgfacde
E) bgafdce
73. A string under tension carries transverse waves traveling at speed v. If the same
string is under four times the tension, what is the wave speed?
A) v
B) 2v
C) v/2
D) 4v
E) v/4
20 74. A string under tension carries a transverse wave traveling at speed v. If the linear
density of the string is halved, what is the wave speed?
A) The wave speed is unchanged.
B) The wave speed is halved.
C) The wave speed is quadrupled.
D) The wave speed decreases to about 71% of v.
E) The wave speed increases by about 41%.
75. A string under tension carries a transverse wave traveling at speed v. If the tension in
the string is quadrupled and the linear density of the string is doubled, what is the
wave speed?
A) The wave speed is unchanged.
B) The wave speed is halved.
C) The wave speed is quadrupled.
D) The wave speed decreases to about 71% of v.
E) The wave speed increases by about 41%.
76. Sound travels at 340 m/s in air and 1500 m/s in water. A sound of 256 Hz is made
under water. In the air,
A) the frequency remains the same but the wavelength is shorter.
B) the frequency is higher but the wavelength stays the same.
C) the frequency is lower but the wavelength is longer.
D) the frequency is lower and the wavelength is shorter.
E) both the frequency and the wavelength remain the same.
77. A string of mass 2.4 × 10–3 kg and length 0.60 m vibrates transversely in such a way
that its fundamental frequency is 100 Hz. The tension on this string must be
approximately
A) 0.16 N
B) 0.32 N
C) 13 N
D) 26 N
E) 58 N
21 78. A stationary ship generates a sound signal at the bow and has a receiver system at the
stern of the ship 100 m away. The difference in time between the signal arriving at
the stern traveling directly through the air and the signal reflected from the sea
bottom is 0.5 second. If the velocity of sound in air is 331 m/s and in water is 1435
m/s, calculate the depth of water below the ship.
A) 1150 m
B) 574 m
C) 359 m
D) 396 m
E) 450 m
79. A traveling wave passes a point of observation. At this point, the time between
successive crests is 0.2 s. Which of the following statements can be justified?
A) The wavelength is 5 m.
B) The frequency is 5 Hz.
C) The velocity of propagation is 5 m/s.
D) The wavelength is 0.2 m.
E) There is not enough information to justify any of these statements.
80. The equation of a traveling wave is
y(x, t) = 0.02 cos(0.25x – 500t)
where the units are SI. The velocity of the wave is
A) 4.0 m/s
B) 10 m/s
C) 0.13 km/s
D) 0.50 km/s
E) 2.0 km/s
81. A sinusoidal wave train is moving along a string. The equation giving the
displacement y of a point at coordinate x has the form
y(x, t) = 0.15 sin[10π(t – x/60)]
where the units are SI. The wavelength is
A) 8.0 cm
B) 15 cm
C) 6.0 m
D) 12 m
E) 60 m
22 82. If you were to reduce the amplitude of a wave on a string by half while keeping the
speed and frequency of the wave constant, the energy delivered by the wave would
A) double.
B) quadruple.
C) be reduced 50%.
D) be reduced to 25% of its previous value.
E) be unchanged.
83. If you were to double the speed of a wave on a string while keeping the frequency
and amplitude of the wave constant, the rate at which energy is delivered by the
wave would
A) double.
B) quadruple.
C) be reduced 50%.
D) be reduced to 25% of its previous value.
E) be unchanged.
84. Waves of amplitude 1.1 cm and wavelength 40 cm move along a 12-m long string
that has a mass of 70 g and is under a tension of 15 N. Calculate the velocity of the
wave.
A) 51 m/s
B) 2570 m/s
C) 16 m/s
D) 15 m/s
E) 331 m/s
85. A wave of frequency f is transmitted on a string with tension T. If the tension is
increased by a factor of 4 and the frequency and amplitude are unchanged, the
power transmitted changed by
A) 1/2
B) 1/4
C) 2
D) 4
E) 1
23 86. You have a rope that is 10 m long and has a mass of 0.2 kg. In addition, you have an
oscillator that can generate a 5 Hz wave with an amplitude of 10 cm. What should
the tension in the rope be if you need to transmit 10 W of power along the rope?
A) 102 N
B) 205 N
C) 320 N
D) 51 N
E) 250 N
87. The intensity of a certain spherical wave is 8.0 W/m2 at a distance of 1.0 m from the
source. If the medium is isotropic and nonabsorbing, the intensity 100 m from the
source is
A) 8.0 W/m2
B) 6.4 × 10–4 W/m2
C) 1.9 × 10–4 W/m2
D) 8.0 × 10–4 W/m2
E) 1.9 × 10–6 W/m2
88. The intensity of a wave at a certain point is I. A second wave has twice the energy
density and three times the speed of the first. What is the intensity of the second
wave?
A) I
B) 2I
C) 3I
D) 6I
E) 2I/3
89. We can hear sounds that are produced around a corner but cannot see light that is
produced around a corner because
A) light travels only in straight lines whereas sound can travel in a curved path.
B) sound has more energy than light.
C) sound has shorter wavelengths than light.
D) sound has longer wavelengths than light.
E) None of these is correct.
24 90. A cord stretched to a tension FT, consists of two sections whose linear densities are ì1
and ì2 (< µ1). A wave of frequency f and speed v is sent along the cord from one end.
Which of the following statements is true about the transmitted and reflected waves?
A) Both the transmitted and reflected waves have the same speed, v.
B) Both the transmitted and reflected waves have the same frequency, f.
C) Both the transmitted and reflected waves have the same wavelength, λ = v/f.
D) The reflected wave is inverted compared to the transmitted wave.
E) none of the above
91. A pulse moves in a string toward a free end (a ring on a post) as indicated in the
sketch.
On reflection, the pulse would most nearly be represented by
A) 1
B) 2
C) 3
D) 4
E) 5
25 92.
The pulse shown is moving in the string toward a fixed end at the wall. After
reflection at the wall, which figure correctly represents the pulse?
A) 1
B) 2
C) 3
D) 4
E) 5
93.
From the figure above, you can conclude that
A) the medium to the left of the boundary is denser than the medium to the right.
B) the medium to the right of the boundary is denser than the medium to the left.
C) the pulse is initially traveling from right to left.
D) the wave has lost energy as a result.
E) None of these is correct.
26 94.
From the figure, you can conclude that
A) the wave travels slower in the medium to the left of the interface than in the medium
to the right of the interface.
B) the wave travels faster in the medium to the left of the interface than in the medium to
the right of the interface.
C) the wave is traveling with the same speed on both sides of the interface.
D) the angle of incidence is equal to the angle of refraction.
E) total internal reflection is not possible for a wave traveling from left to right.
Answer Key
1. B
2. D
3. C
4. D
5. B
6. D
7. C
8. A
9. D
10. C
11. A
12. B
13. E
14. B
15. D
16. C
17. D
18. E
19. B
27 20. D
21. C
22. B
23. D
24. D
25. B
26. B
27. D
28. C
29. C
30. D
31. E
32. C
33. E
34. E
35. A
36. B
37. D
38. B
39. E
40. A
41. D
42. C
43. B
44. D
45. D
46. B
47. A
48. A
49. C
50. B
51. E
52. B
53. D
54. E
55. E
56. B
57. C
58. C
59. B
60. A
61. D
62. A
63. D
64. B
65. A
28 66. A
67. B
68. A
69. D
70. D
71. C
72. D
73. B
74. E
75. E
76. A
77. E
78. B
79. B
80. E
81. D
82. D
83. A
84. A
85. C
86. B
87. D
88. D
89. D
90. B
91. B
92. D
93. A
94. A
29