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2000 by Harcourt College Publishers. All rights reserved.

Chapter 34

Electromagnetic Waves

Multiple Choice

1. The Earth is 1.49 1011 meters from the sun. If the solar radiation at the top of theEarth's atmosphere is 1340 W/m2, what is the total power output of the sun?

a . 7 1027 Wb. 2 1030 Wc. 6.62 1026 Wd. 3.73 1026 We. 2.98 1025 W

2. If the radiant energy from the sun comes in as a plane EM wave of intensity 1340 W/m2,calculate the peak values of E and B.

a . 300 V/m, 104 Tb. 1000 V/m, 3.3 106 Tc. 225 V/m, 1.6 103 Td. 111 V/m, 3 105 Te. 710 V/m, 2.3 106 T

3. If the maximum E-component of an electromagnetic wave is 600 V/m, what is themaximum B-component?

a . 1.4 Teslab. 1.8 105 Tc. 2 106 Td. 103 Te. 1.6 1010 T

4. Find the force exerted by reflecting sunlight off a reflecting aluminum sheet in space ifthe area normal to the sunlight is 10,000 m2 and the solar intensity is 1350 W/m2.

a . 0.72 Nb. 0.09 Nc. 9 Nd. 45 Ne. 0.18 N

5. What is the average value of the magnitude of the Poynting vector S at 1 meter from a100-watt lightbulb radiating in all directions?

a . 1 W/m2b. 4 W/m2c. 2 W/m2d. 8 W/m2e. 12 W/m2

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6. A 100-kW radio station emits EM waves in all directions from an antenna on top of amountain. What is the intensity of the signal at a distance of 10 km?

a . 8 105 W/m2b. 8 106 W/m2c. 3mW/m2d. 0.8 W/m2e. 2.5 105 W/m2

7. Determine the amount of energy carried in 1 meter of a 3.5-milliwatt He-Ne laser beam ifthe cross-sectional area of the beam is 5 106 m2.

a . 1.7 1011 Jb. 3.3 106 Jc. 1.2 1011 Jd. 2.3 106 Je. 4.2 103 J

8. How much electromagnetic energy is contained per cubic meter near the Earth's surface ifthe intensity of sunlight under clear skies is 1000 W/m2?

a . 3.3 106 Jb. 3.3 Jc. 0.003 Jd. 104 Je. 3.0 105 J

9. At a distance of 10 km from a radio transmitter, the amplitude of the E-field is.20 volts/meter. What is the total power emitted by the radio transmitter?

a . 10 kWb. 67 kWc. 140 kWd. 245 kWe. 21 kW

10. What is the maximum radiation pressure exerted by sunlight in space (S = 1350 W/m2) ona flat black surface?

a . 2.25 105 Pab. 0.06 Pac. 7 104 Pad. 4.5 106 Pae. 9.0 106 Pa

11. What is the maximum radiation pressure exerted by sunlight in space (S = 1350 W/m2) ona highly polished silver surface?

a . 1.4 102 Pab. 0.12 Pac. 9.0 106 Pad. 4.5 105 Pae. 2.3 106 Pa

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12. Find the frequency of X-rays of wavelength 1 A = 1010 m.

a . 3 1018 Hzb. 3 1010 MHzc. 6 109 Hzd. 3 108 Hze. 3 1020 Hz

13. Green light has a wavelength of 5.4 107 m. What is the frequency of this EM-wave inair?

a . 5.55 1014 Hzb. 6 1011 Hzc. 9 108 Hzd. 3 1010 MHze. 1.8 1015 Hz

14. An FM radio station broadcasts at 98.6 MHz. What is the wavelength of theradiowaves?

a . 60.8 mb. 6.08 mc. 3.04 md. 0.314 me. 0.33 cm

15. What should be the height of a dipole antenna (of dimensions 1/4 wavelength) if it is totransmit 1200 kHz radiowaves?

a . 11.4 mb. 60 cmc. 1.12 md. 62.5 me. 250 m

16. The magnetic field of a plane-polarized electromagnetic wave moving in the z-direction

is given by B = 1.2 106 sin 2 z

240 t 107

8 in SI units. What is the maximum

E-field?

a . 1000 V/m b. 180 V/m c. 81 V/m d. 360 V/m e. 0.40 V/m

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240 t 107

8 in SI units. What is the frequency of the

wave?

a . 500 MHz b. 250 kHz c. 1.25 MHz d. 10 mHz e. 300 MHz



240 t 107

8 in SI units. What is the wavelength of

the EM wave?

a . 120 m b. 240 m c. 60 m d. 100 m e. 360 m



240 t 107

8 in SI units. What is the speed of the EM

wave?

a . 3 108 m/s b. 100 m/s c. 106 m/s d. 2 107 m/s e. 2 108 m/s



240 t 107

8 in SI units. Find the average power per

square meter carried by the EM wave.

a . 720 W b. 172 W c. 500 W d. 2 107 W e. 86 W

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21. A loop antenna consists of 500 loops of copper wire, 10 cm in diameter. If an incoming EMwave has a frequency 1000 kHz and has a B-vector (maximum magnitude of 1010 T), whatis the induced voltage (rms) in the loop?

a . 33.4 mVb. 0.007 Vc. 1.74 mVd. 22.4 mVe. 2.34 mV

22. A solar cell has a light-gathering area of 10 cm2 and produces 0.2 A at 0.8 V (DC) whenilluminated with S = 1000 W/m2 sunlight. What is the efficiency of the solar cell?

a . 16%b. 7%c. 23%d. 4%e. 32%

Conceptual Problems

23. Near the surface of the planet, the Earth's magnetic field is about 0.5 104 T. How muchenergy is stored in 1 m3 of the atmosphere because of this field?

24. The sun radiates energy at a rate of 3.86 1026 W. Its radius is 7.0 108 m. If the distancefrom the Earth to the sun is 1.5 1011 m, what is the intensity of solar radiation at thetop of the Earth's atmosphere?

25. A possible means of spaceflight is to place a perfectly reflecting aluminized sheet intoEarth orbit and use the light from the sun to push this solar sail. If a huge sail of area6 105 m2 and mass 6000 kg were placed into orbit and turned toward the sun, what wouldbe the force exerted on the sail? (Assume a solar intensity of 1380 W/m2.)

26. High frequency alternating current is passed through a solenoid that contains a solidcopper core insulated from the coils of the solenoid. Which statement is correct?

a . A copper core remains cool no matter what the frequency of the current in the solenoidis.

b. The copper core remains cool because the induced emf is parallel to the solenoid axisand fluctuates rapidly.

c. The copper core heats up because an emf parallel to the solenoid axis is induced in thecore.

d. The copper core heats up because circular currents around its axis are induced in thecore.

e. The copper core heats up because the electric field induced in the copper is parallel tothe magnetic field produced by the solenoid.

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27. In an electromagnetic wave, 1) how are the electric and magnetic field directions relatedand 2) how is the direction of travel determined from their directions? (c is the velocityof the light wave.)

a . E || B; cc =

E B|E B| .

b. E || B; cc =

B E|B E| .

c. E B; cc =

E B|E B| .

d. E B; cc =

B E|B E| .

e. E = B/c; cc =

B E|B E| .

28. The intensity of radiation reaching the earth from the sun is 1350 W/m2. The earth'sradius is 6.4 106 m. How big a force does this radiation exert on the earth? (Assume it isall absorbed.)

a . 5.8 108 Nb. 1.2 109 Nc. 2.3 109 Nd. 4.6 109 Ne. 1.7 1017 N

Chapter 34 1


Chapter 34

Electromagnetic Waves

1. Answer: d

2. Answer: b

3. Answer: c

4. Answer: b

5. Answer: d

6. Answer: a

7. Answer: c

8. Answer: a

9. Answer: b

10. Answer: d

11. Answer: c

12. Answer: a

13. Answer: a

14. Answer: c

15. Answer: d

16. Answer: d

17. Answer: c

18. Answer: b

19. Answer: a

20. Answer: b

21. Answer: c

22. Answer: a

23. Answer: 103 J

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24. Answer: 1350 W/m2

25. Answer: 5.52 N

26. Answer: d

27. Answer: c

28. Answer: a

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