# Physics chapter 33 Electromagnetic Waves, Other for Physics. University of Pittsburgh (PA)

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Fundamentals of Physics 7th Edition: Test Blanks

Chapter 33: ELECTROMAGNETIC WAVES

1. Select the correct statement:

A. ultraviolet light has a longer wavelength than infrared B. blue light has a higher frequency than x rays C. radio waves have higher frequency than gamma rays D. gamma rays have higher frequency than infrared waves E. electrons are a type of electromagnetic wave

ans: D

2. Consider: radio waves (r), visible light (v), infrared light (i), x-rays (x), and ultraviolet light (u). In order of increasing frequency, they are:

A. r, v, i, x, u B. r, i, v, u, x C. i, r, v, u, x D. i, v, r, u, x E. r, i, v, x, u

ans: B

3. The order of increasing wavelength for blue (b), green (g), red (r), and yellow (y) light is:

A. r, y, g, b B. r, g, y, b C. g, y, b, r D. b, g, y, r E. b, y, g, r

ans: D

4. Of the following human eyes are most sensitive to:

A. red light B. violet light C. blue light D. green light E. none of these (they are equally sensitive to all colors)

ans: D

5. Which of the following is NOT true for electromagnetic waves?

A. they consist of changing electric and magnetic fields B. they travel at di erent speeds in vacuum, depending on their frequency C. they transport energy D. they transport momentum E. they can be reflected

ans: B

494 Chapter 33: ELECTROMAGNETIC WAVES

6. The product μ0 0 has the same units as:

A. (velocity)2

B. (velocity)1/2

C. 1/velocity D. 1/velocity2

E. 1/velocity1/2

ans: D

7. Maxwell’s equations predict that the speed of electromagnetic waves in free space is given by:

A. μ0 0 B. (μ0 0)

1/2

C. 1/μ0 0 D. 1/(μ0 0)

1/2

E. 1/(μ0 0) 2

ans: D

8. Maxwell’s equations predict that the speed of light in free space is

A. an increasing function of frequency B. a decreasing function of frequency C. independent of frequency D. a function of the distance from the source E. a function of the size of the source

ans: C

9. The speed of light in vacuum is about:

A. 1100 ft/s B. 93× 106 m/s C. 6× 1023 m/s D. 3× 1010 cm/s E. 186, 000mph

ans: D

10. The Sun is about 1.5 × 1011 m away. The time for light to travel this distance is about: A. 4.5× 1018 s B. 8 s C. 8min D. 8 hr E. 8 yr

ans: C

Chapter 33: ELECTROMAGNETIC WAVES 495

11. The time for a radar signal to travel to the Moon and back, a one-way distance of about 3.8× 108 m, is: A. 1.3 s B. 2.5 s C. 8 s D. 8min E. 1× 106 s

ans: B

12. Which of the following types of electromagnetic radiation travels at the greatest speed in vacuum?

A. Radio waves B. Visible light C. X rays D. Gamma rays E. All of these travel at the same speed

ans: E

13. Radio waves di er from visible light waves in that radio waves:

A. travel slower B. have a higher frequency C. travel faster D. have a lower frequency E. require a material medium

ans: D

14. Visible light has a frequency of about:

A. 5× 1018 Hz B. 5× 1016 Hz C. 5× 1014 Hz D. 5× 1012 Hz E. 5× 1010 Hz

ans: C

15. The theoretical upper limit for the frequency of electromagnetic waves is:

A. just slightly greater than that of red light B. just slightly less than that of blue light C. the greatest x-ray frequency D. none of the above (there is no upper limit) E. none of the above (but there is an upper limit)

ans: D

496 Chapter 33: ELECTROMAGNETIC WAVES

16. Radio waves of wavelength 3 cm have a frequency of:

A. 1MHz B. 9MHz C. 100MHz D. 10, 000MHz E. 900MHz

ans: D

17. Radio waves of wavelength 300m have a frequency of:

A. 10 3 kHz B. 500 kHz C. 1MHz D. 9MHz E. 108 kHz

ans: C

18. If the electric field in a plane electromagnetic wave is given by Em sin[(3×106 m 1)x t], the value of is:

ans: D

19. An electromagnetic wave is generated by:

A. any moving charge B. any accelerating charge C. only a charge with changing acceleration D. only a charge moving in a circle E. only a charge moving in a straight line

ans: B

Chapter 33: ELECTROMAGNETIC WAVES 497

20. The electric field for a plane electromagnetic wave traveling in the +y direction is shown. Consider a point where E is in the +z direction. The B field is:

............................................................................................................................................................................................................... y.....

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A. in the +x direction and in phase with the E field B. in the x direction and in phase with the E field C. in the +x direction and one-fourth of a cycle out of phase with the E field D. in the +z direction and in phase with the E field E. in the +z direction and one-fourth of a cycle out of phase with the E field

ans: A

21. A plane electromagnetic wave is traveling in the positive x direction. At the instant shown the electric field at the extremely narrow dashed rectangle is in the negative z direction and its magnitude is decreasing. Which diagram correctly shows the directions and relative magnitudes of the magnetic field at the edges of the rectangle?

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E

ans: B

22. In a plane electromagnetic wave in vacuum, the ratio E/B of the amplitudes in SI units of the two fields is:

A. the speed of light B. an increasing function of frequency C. a decreasing function of frequency D. 2 E. 1/ 2

ans: A

498 Chapter 33: ELECTROMAGNETIC WAVES

23. If the magnetic field in a plane electromagnetic wave is along the y axis and its component is given by Bm sin(kx t), in SI units, then the electric field is along the z axis and its component is given by:

A. (cBm) cos(kx t) B. (cBm/c) cos(kx t) C. (cBm/c) sin(kx t) D. Bm cos(kx t) E. (cBm/c) sin(kx t)

ans: E

24. If the electric field in a plane electromagnetic wave is along the y axis and its component is given by Em sin(kx+ t), in SI units, then the magnetic field is along the z axis and its component is given by:

A. (Em/c) cos(kx+ t) B. (Em/c) cos(kx+ t) C. (Em/c) sin(kx+ t) D. Em cos(kx+ t) E. (Em/c) sin(kx+ t)

ans: C

25. An electromagnetic wave is traveling in the positive x direction with its electric field along the z axis and its magnetic field along the y axis. The fields are related by:

A. E/ x = μ0 0 B/ x B. E/ x = μ0 0 B/ t C. B/ x = μ0 0 E/ x D. B/ x = μ0 0 E/ t E. B/ x = μ0 0 E/ t

ans: E

26. If the amplitude of the electric field in a plane electromagnetic wave is 100V/m then the amplitude of the magnetic field is:

A. 3.3× 10 7 T B. 6.7× 10 7 T C. 0.27T D. 8.0× 107 T E. 3.0× 109 T

ans: A

27. For an electromagnetic wave the direction of the vector E ×B gives: A. the direction of the electric field B. the direction of the magnetic field C. the direction of wave propagation D. the direction of the electromagnetic force on a proton E. the direction of the emf induced by the wave

ans: C

Chapter 33: ELECTROMAGNETIC WAVES 499

28. The dimensions of S = (1/μ0)E ×B are: A. J/m2

B. J/s C. W/s D. W/m2

E. J/m3

ans: D

29. The time-averaged energy in a sinusoidal electromagnetic wave is:

A. overwhelmingly electrical B. slightly more electrical than magnetic C. equally divided between the electric and magnetic fields D. slightly more magnetic than electrical E. overwhelmingly magnetic

ans: C

30. At a certain point and a certain time the electric field of an electromagnetic wave is in the negative z direction and the magnetic field is in the positive y direction. Which of the following statements is true?

A. Energy is being transported in the positive x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the negative x direction

B. Energy is being transported in the positive x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the positive x direction

C. Energy is being transported in the negative x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the positive x direction

D. Energy is being transported in the negative x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the negative x direction

E. None of the above are true

ans: B

31. An electromagnetic wave is transporting energy in the negative y direction. At one point and one instant the magnetic field is in the positive x direction. The electric field at that point and instant is:

A. positive y direction B. negative y direction C. positive z direction D. negative z direction E. negative x direction

ans: D

500 Chapter 33: ELECTROMAGNETIC WAVES

32. A point source emits electromagnetic energy at a rate of 100W. The intensity 10m from the source is:

A. 10W/m 2

B. 1.6W/m 2

C. 1W/m2

D. 0.024W/m 2

E. 0.080W/m 2

ans: E

33. The light intensity 10m from a point source is 1000W/m 2 . The intensity 100m from the same

source is:

A. 1000W/m 2

B. 100W/m 2

C. 10W/m2

D. 1W/m 2

E. 0.1W/m 2

ans: C

34. When the distance between a point source of light and a light meter is reduced from 6.0m to 2.0m, the intensity of illumination at the meter will be the original value multiplied by:

A. 3 B. 9 C. 1/3 D. 1/9 E. 1

ans: A

35. The magnetic field in a sinusoidal light wave has an amplitude of 3.3 × 10 7 T. The intensity of the wave is:

A. 1.7× 10 4 W/m2 B. 13W/m

2

C. 27W/m2

D. 1.0× 105 W/m2 E. 4.0× 1010 W/m2

ans: B

36. A sinusoidal electromagnetic wave with an electric field amplitude of 100V/m is incident nor- mally on a surface with an area of 1 cm2 and is completely absorbed. The energy absorbed in 10 s is:

A. 1.3mJ B. 13mJ C. 27mJ D. 130mJ E. 270mJ

ans: B

Chapter 33: ELECTROMAGNETIC WAVES 501

37. Evidence that electromagnetic waves carry momentum is:

A. the tail of a comet points away from the Sun B. electron flow through a wire generates heat C. a charged particle in a magnetic field moves in a circular orbit D. heat can be generated by rubbing two sticks together E. the Doppler e ect

ans: A

38. Light of uniform intensity shines perpendicularly on a totally absorbing surface, fully illumi- nating the surface. If the area of the surface is decreased:

ans: D

39. Light with an intensity of 1 kW/m 2 falls normally on a surface and is completely absorbed.

A. 1 kPa B. 3× 1011 Pa C. 1.7× 10 6 Pa D. 3.3× 10 6 Pa E. 6.7× 10 6 Pa

ans: D

40. Light with an intensity of 1 kW/m 2 falls normally on a surface and is completely reflected. The

A. 1 kPa B. 3× 1011 Pa C. 1.7× 10 6 Pa D. 3.3× 10 6 Pa E. 6.7× 10 6 Pa

ans: E

41. Light with an intensity of 1 kW/m 2 falls normally on a surface with an area of 1 cm2 and is

completely absorbed. The force of the radiation on the surface is:

A. 1.0× 10 4 N B. 3.3× 10 11 N C. 1.7× 10 10 N D. 3.3× 10 10 N E. 6.7× 10 10 N

ans: D

502 Chapter 33: ELECTROMAGNETIC WAVES

42. Light with an intensity of 1 kW/m 2 falls normally on a surface with an area of 1 cm2 and is

completely reflected. The force of the radiation on the surface is:

A. 1.0× 10 4 N B. 3.3× 10 11 N C. 1.7× 10 10 N D. 3.3× 10 10 N E. 6.7× 10 10 N

ans: E

43. A company claims to have developed material that absorbs light energy without a transfer of momentum. Such material is:

A. impossible B. possible, but very expensive C. inexpensive and already in common use D. in use by NASA but is not commercially available E. a breakthrough in high technology

ans: A

44. Polarization experiments provide evidence that light is:

A. a longitudinal wave B. a stream of particles C. a transverse wave D. some type of wave E. nearly monochromatic

ans: C

45. A vertical automobile radio antenna is sensitive to electric fields that are polarized:

A. horizontally B. in circles around the antenna C. vertically D. normal to the antenna in the forward direction E. none of the above

ans: C

46. For linearly polarized light the plane of polarization is:

A. perpendicular to both the direction of polarization and the direction of propagation B. perpendicular to the direction of polarization and parallel to the direction of propagation C. parallel to the direction of polarization and perpendicular to the direction of propagation D. parallel to both the direction of polarization and the direction of propagation E. none of the above

ans: D

Chapter 33: ELECTROMAGNETIC WAVES 503

47. Light from any ordinary source (such as a flame) is usually:

A. unpolarized B. plane polarized C. circularly polarized D. elliptically polarized E. monochromatic

ans: A

48. The electric field in unpolarized light:

A. has no direction at any time B. rotates rapidly C. is always parallel to the direction of propagation D. changes direction randomly and often E. remains along the same line but reverses direction randomly and often

ans: D

49. The diagrams show four pairs of polarizing sheets, with the polarizing directions indicated by dashed lines. The two sheets of each pair are placed one behind the other and the front sheet is illuminated by unpolarized light. The incident intensity is the same for all pairs of sheets. Rank the pairs according to the intensity of the transmitted light, least to greatest.

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A. 1, 2, 3, 4 B. 4, 2, 1, 3 C. 2, 4, 3, 1 D. 2, 4, 1, 3 E. 3, 1, 4, 2

ans: D

504 Chapter 33: ELECTROMAGNETIC WAVES

50. A clear sheet of polaroid is placed on top of a similar sheet so that their polarizing axes make an angle of 30 with each other. The ratio of the intensity of emerging light to incident unpolarized light is:

A. 1 : 4 B. 1 : 3 C. 1 : 2 D. 3 : 4 E. 3 : 8

ans: E

51. An unpolarized beam of light has intensity I0. It is incident on two ideal polarizing sheets. The angle between the axes of polarization of these sheets is . Find if the emerging light has intensity I0/4:

A. sin 1(1/2) B. sin 1(1/ 5) C. cos 1(1/2) D. cos 1(1/ 2) E. tan 1(1/4)

ans: D

52. In a stack of three polarizing sheets the first and third are crossed while the middle one has its axis at 45 to the axes of the other two. The fraction of the intensity of an incident unpolarized beam of light that is transmitted by the stack is:

A. 1/2 B. 1/3 C. 1/4 D. 1/8 E. 0

ans: D

53. Three polarizing sheets are placed in a stack with the polarizing directions of the first and third perpendicular to each other. What angle should the polarizing direction of the middle sheet make with the polarizing direction of the first sheet to obtain maximum transmitted intensity when unpolarized light is incident on the stack?

A. 0 B. 30 C. 45 D. 60 E. 90

ans: C

Chapter 33: ELECTROMAGNETIC WAVES 505

54. Three polarizing sheets are placed in a stack with the polarizing directions of the first and third perpendicular to each other. What angle should the polarizing direction of the middle sheet make with the polarizing direction of the first sheet to obtain zero transmitted intensity when unpolarized light is incident on the stack?

A. 0 B. 30 C. 45 D. 60 E. All angles allow light to pass through

ans: A

55. The relation incident = reflected, which applies as a ray of light strikes an interface between two media, is known as:

A. Faraday’s law B. Snell’s law C. Ampere’s law D. Cole’s law E. none of these

ans: E

56. The relation n1 sin 1 = n2 sin 2, which applies as a ray of light strikes an interface between two media, is known as:

A. Gauss’ law B. Snell’s law C. Faraday’s law D. Cole’s law E. law of sines

ans: B

57. As used in the laws of reflection and refraction, the “normal” direction is:

A. any convenient direction B. tangent to the interface C. along the incident ray D. perpendicular to the electric field vector of the light E. perpendicular to the interface

ans: E

58. When an electromagnetic wave meets a reflecting surface, the direction taken by the reflected wave is determined by:

A. the material of the reflecting surface B. the angle of incidence C. the index of the medium D. the intensity of the wave E. the wavelength

ans: B

506 Chapter 33: ELECTROMAGNETIC WAVES

59. The index of refraction of a substance is:

A. the speed of light in the substance B. the angle of refraction C. the angle of incidence D. the speed of light in vacuum divided by the speed of light in the substance E. measured in radians

ans: D

60. The units of index of refraction are:

A. m/s B. s/m C. radian D. m/s2

E. none of these

ans: E

61. The diagram shows the passage of a ray of light from air into a substance X. The index of refraction of X is:

air X

...

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50 ............... 40

................... .

20

........................ 70

.......................... .. ... ...................................................................

... ..... .

A. 0.53 B. 0.88 C. 1.9 D. 2.2 E. 3.0

ans: C

Chapter 33: ELECTROMAGNETIC WAVES 507

62. If nwater = 1.33, what is the angle of refraction for the ray shown?

air water

............... ....

30

....................60

.... .... .... .... .... .... .... .... .... .... ........ .....

A. 19 B. 22 C. 36 D. 42 E. 48

ans: D

63. Which diagram below illustrates the path of a light ray as it travels from a given point X in air to another given point Y in glass?

•Y

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A

•Y

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B

•Y

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C

•Y

•X ..... ..... ..... ......... ..... ..... .......... ..... ..... ....

D

•Y

•X ..... ..... ..... ...... .... . .... .... ........... .... .... ....

E

ans: E

508 Chapter 33: ELECTROMAGNETIC WAVES

64. The index of refraction for diamond is 2.5. Which of the following is correct for the situation shown?

diamond

air

...........

a

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............... ...... .... ... ... .

c

...

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b

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A. (sin a)/(sin b) = 2.5 B. (sin b)/(sin d) = 2.5 C. (cos a)/(cos c) = 2.5 D. (sin c)/(sin a) = 2.5 E. a/c = 2.5

ans: D

65. When light travels from medium X to medium Y as shown:

X

Y

............................... .. ... ......................................................

. .....

A. both the speed and the frequency decrease B. both the speed and the frequency increase C. both the speed and the wavelength decrease D. both the speed and the wavelength increase E. both the wavelength and the frequency are unchanged

ans: C

66. A ray of light passes obliquely through a plate of glass having parallel faces. The emerging ray:

A. is totally internally reflected B. is bent more toward the normal than the incident ray C. is bent further away from the normal than the incident ray D. is parallel to the incident ray but displaced sideways E. lies on the same straight line as the incident ray

ans: D

Chapter 33: ELECTROMAGNETIC WAVES 509

67. When light passes from air to glass, it bends:

A. toward the normal without changing speed B. toward the normal and slows down C. toward the normal and speeds up D. away from the normal and slows down E. away from the normal and speeds up

ans: B

68. A ray of light passes through three media as shown. The speed of light in these media obey:

medium 1

medium 2

medium 3

............................ .. ... ...................................

. ..... . ................................................. ...

..

A. v1 > v2 > v3 B. v3 > v2 > v1 C. v3 > v1 > v2 D. v2 > v1 > v3 E. v1 > v3 > v2

ans: C

69. As light goes from one medium to another, it is bent away from the normal. Then:

A. the speed of the light has increased B. dispersion must occur C. the second medium has a higher index of refraction than the first D. no change in speed has occurred E. refraction has not occurred because refraction means a bending toward the normal

ans: A

70. A pole stands in a river, half in and half out of the water. Another pole of the same length stands vertically on the shore at a place where the ground is level. The shadow cast by the pole in the river on the river bottom is:

A. slightly longer than the shadow of the pole on land B. much longer than the shadow of the pole on land C. shorter than the shadow of the pole on land D. shorter than the shadow of the pole on land if the Sun is high and longer if the sun is low E. the same length as the shadow of the pole on land

ans: C

510 Chapter 33: ELECTROMAGNETIC WAVES

71. The rectangular metal tank shown is filled with an unknown liquid. The observer, whose eye is level with the top of the tank, can just see corner E. The index of refraction of this liquid is:

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eye

4 ft

3 ft

E

A. 1.75 B. 1.67 C. 1.50 D. 1.33 E. 1.25

ans: E

72. The index of refraction of benzene is 1.80. The critical angle for total internal reflection, at a benzene-air interface, is about:

A. 56 B. 47 C. 34 D. 22 E. 18

ans: C

73. The index of refraction of a certain glass is 1.50. The sine of the critical angle for total internal reflection at a glass-air interface is:

A. 0.50 B. 0.67 C. 0.75 D. 1.00 E. 1.50

ans: B

Chapter 33: ELECTROMAGNETIC WAVES 511

74. The illustration shows total internal reflection taking place in a piece of glass. The index of refraction of this glass:

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air

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A. is at least 2.0 B. is at most 2.0 C. is at least 1.15 D. is at most 1.15 E. cannot be calculated from the given data

ans: C

75. The critical angle for total internal reflection at a diamond-air interface is 25 . Suppose light is incident at an angle of with the normal. Total internal reflection will occur if the incident medium is:

A. air and = 25 B. air and > 25 C. air and < 25 D. diamond and < 25 E. diamond and > 25

ans: E

76. If nwater = 1.50 and nglass = 1.33, then total internal reflection at an interface between this glass and water:

A. occurs whenever the light goes from glass to water B. occurs whenever the light goes from water to glass C. may occur when the light goes from glass to water D. may occur when the light goes from water to glass E. can never occur at this interface

ans: D

77. The separation of white light into colors by a prism is associated with:

A. total internal reflection B. partial reflection from each surface C. variation of index of refraction with wavelength D. a decrease in the speed of light in the glass E. selective absorption of various colors

ans: C

512 Chapter 33: ELECTROMAGNETIC WAVES

78. The diagram shows total internal reflection. Which of the following statements is NOT true?

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medium I

medium II

N

O

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A B

A. Angle AON is the angle of incidence B. Angle AON = angle BON C. Angle AON must be the critical angle D. The speed of light in medium II is greater than that in medium I E. if angle AON were increased, there would still be total internal reflection

ans: C

79. A ray of light in water (index n1) is incident on its surface (with air) at the critical angle for total internal reflection. Some oil (index n2) is now floated on the water. The angle between the ray in the oil and the normal is:

A. sin 1(1.00) B. sin 1(1/n1) C. sin 1(1/n2) D. sin 1(n1/n2) E. sin 1(n2/n1)

ans: C

Chapter 33: ELECTROMAGNETIC WAVES 513