Download 02-01/02 Intro to Light and Electromagnetic waves Problem Set

Introduction to Light and Electormagnetic Waves Exercises
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____
1. Electromagnetic waves are
a. transverse waves.
b. longitudinal waves.
____
2. Electromagnetic waves
a. need a medium to travel through.
b. can travel through a vacuum.
____
3. Which of these electromagnetic waves has the shortest wavelength?
a. Infrared waves
b. Light waves
c. Radio waves
d. X-rays
e. Ultraviolet waves
____
4. Compared to the wavelength of ultraviolet waves, the wavelength of infrared waves is
a. the same.
b. shorter.
c. longer.
____
5. Compared to the velocity of radio waves, the velocity of visible light waves is
a. slower.
b. faster.
c. the same.
____
6. The source of all electromagnetic waves is
a. magnetic fields.
b. heat.
c. electric fields.
d. vibrating charges.
e. none of the above
____
7. Which of the following are fundamentally different from the others?
a. Gamma rays
b. Radio waves
c. Sound waves
d. Light waves
e. X-rays
____
8. The main difference between a radio wave and a light wave is its
a. speed.
b. wavelength.
c. both A and B
d. none of the above.
____
9. The main difference between a radio wave and a sound wave is its
a. basic nature.
b.
c.
d.
e.
amplitude.
energy.
frequency.
wavelength.
____ 10. If the sun were to disappear right now, we wouldn't know about it for 8 minutes because it takes 8 minutes
a. to operate receiving equipment in the dark.
b. for light to travel from the sun to Earth.
c. for the sun to disappear.
d. all of the above
e. none of the above
____ 11. Which of the following is NOT an electromagnetic wave?
a. Sound
b. Radio
c. Light
d. Infrared
e. X-ray
____ 12. Heat lamps give off mostly
a. X-rays.
b. infrared waves.
c. ultraviolet waves.
d. microwaves.
e. radio waves.
____ 13. Compared to its speed in air, the speed of light in water is
a. slower.
b. the same.
c. faster.
____ 14. Glass is transparent to visible light, but not to
a. ultraviolet.
b. infrared.
c. both a and b.
d. none of the above
____ 15. The shiny surfaces of metals have most to do with
a. metals' relatively high density.
b. a resonant frequency of electrons in the metal.
c. the fact that light reflects from metals.
d. the free electrons in metal atoms.
____ 16. Clouds
a. neither block nor transmit UV light.
b. block UV light.
c. transmit UV light.
____ 17. Electromagnetic waves with higher frequencies have wavelengths that are
a. shorter.
b. longer.
____ 18. The shadow produced by an object held close to a piece of paper in sunlight will be
a. sharp.
b. fuzzy.
____ 19. Solar eclipses are seen less commonly than lunar eclipses because
a. the sun is so much larger than the moon.
b. the sun is farther from Earth than is the moon.
c. solar eclipses don't happen as often as lunar eclipses.
d. Earth's shadow on the moon is larger than the moon's shadow on Earth.
e. none of the above
____ 20. Light waves are
a. longitudinal waves.
b. transverse waves.
____ 21. What is the ultimate source of electromagnetic waves?
a. Vibrating atoms
b. Vibrating molecules
c. Radio sets
d. Vibrating charged particles
e. TV antennas
____ 22. The primary purpose of polarized sunglasses is_____.
a. to block ultraviolet rays.
b. to block infrared rays.
c. to block glare from reflections.
d. to look cool.
____ 23. Light does not pass through what kind of materials?
a. transparent
b. opaque
c. neither a nor b
____ 24. How far is a light-second?
a. 5000 km
b. 300,000 km
c. 9,000,000 km
d. 18,000,000 km
e. 95,000,000,000 km
____ 25. Light that reflects at glancing angles from nonmetallic surfaces, such as glass, water, or roads is
a. polarized perpendicular to the surface.
b. polarized parallel to the surface.
c. randomly polarized.
____ 26. Light reflected from a lake surface is polarized
a. randomly.
b. horizontally.
c. vertically.
____ 27. If an electron vibrates up and down 1000 times each second, it generates an electromagnetic wave having a
a. frequency of 1000 Hz.
b. speed of 1000 m/s.
c. period of 1000 s.
d. wavelength of 1000 m.
____ 28. What is the wavelength of an electromagnetic wave that has a frequency of 1 Hz?
a. More than 1 m
b. Less than 1 m
c. 1 m
____ 29. What is the frequency of an electromagnetic wave having a wavelength of 300,000 km?
a. More than 1 Hz
b. Less than 1 Hz
c. 1 Hz
____ 30. After randomly polarized light passes through a polarizer, it is
a. totally blocked.
b. totally polarized.
c. randomly polarized.
d. partially polarized.
____ 31. If two polarizing filters are held with their polarization axes at right angles to each other, the amount of light
transmitted compared to when their axes are parallel is
a. zero.
b. half as much.
c. the same.
d. twice as much.
Essay
32. Which waves are part of the electromagnetic spectrum? What are their approximate frequencies? Give
examples of where you can find each kind of wave.
33. Explain how light is transmitted through glass. Why is ultraviolet radiation not transmitted through glass?
34. Write a short paragraph on polarization. Explain what it is and how we use polarizers. Explain why
sunglasses polarize light vertically.
Introduction to Light and Electormagnetic Waves Exercises
Answer Section
MULTIPLE CHOICE
1. ANS:
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2. ANS:
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3. ANS:
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4. ANS:
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5. ANS:
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8. ANS:
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9. ANS:
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10. ANS:
OBJ:
11. ANS:
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12. ANS:
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13. ANS:
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14. ANS:
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15. ANS:
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19. ANS:
20. ANS:
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21. ANS:
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22. ANS:
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23. ANS:
A
Ph.4.b
B
Ph.4.e
D
Ph.4.e
C
Ph.4.e
C
Ph.4.e
D
Ph.4.e, Ph.4.f
C
Ph.4.e
B
Ph.4.e
A
Ph.4.e
B
27.2
A
Ph.4.e
B
Ph.4.e
A
Ph.4.e, Ph.4.f
C
Ph.4.e, Ph.4.f
D
Ph.4.b, Ph.4.f
C
Ph.4.b, Ph.4.f
A
Ph.4.e
A
D
B
Ph.4.b
D
Ph.4.e
C
Ph.4.b
B
DIF: 1
REF: p. 414
OBJ: 27.7
DIF: 2
REF: p. 407
OBJ: 27.2
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 409
OBJ: 27.4
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
STO: Ph.4.e
DIF: 2
REF: p. 406, p. 407
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 410
OBJ: 27.4
DIF: 2
REF: p. 410
OBJ: 27.4
DIF: 2
REF: p. 411
OBJ: 27.5
DIF: 2
REF: p. 411
OBJ: 27.5
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 1
DIF: 3
DIF: 1
REF: p. 412
REF: p. 413
REF: p. 414
OBJ: 27.6
OBJ: 27.6
OBJ: 27.7
DIF: 2
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 414
OBJ: 27.7
DIF: 1
REF: p. 411
OBJ: 27.5
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24. ANS:
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25. ANS:
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26. ANS:
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27. ANS:
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28. ANS:
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31. ANS:
OBJ:
Ph.4.b, Ph.4.f
B
Ph.4.e
B
Ph.4.b
B
Ph.4.b
A
Ph.4.e, Ph.4.f
A
Ph.4.e
C
Ph.4.e
B
Ph.4.b
A
27.7
DIF: 3
REF: p. 407
OBJ: 27.1
DIF: 2
REF: p. 415
OBJ: 27.7
DIF: 2
REF: p. 415
OBJ: 27.7
DIF: 2
REF: p. 409
OBJ: 27.4
DIF: 3
REF: p. 408
OBJ: 27.3
DIF: 3
REF: p. 408
OBJ: 27.3
DIF: 2
REF: p. 414
OBJ: 27.7
DIF: 2
STO: Ph.4.b
REF: p. 414, p. 415
ESSAY
32. ANS:
Radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays are all
part of the electromagnetic spectrum. Their approximate frequencies are 103 to 106 Hz, 107 to 1010 Hz, 1011 to
1014 Hz, 1014 Hz, 1015 to 1016 Hz, 1017 Hz, and 1018 Hz respectively. Radio waves are emitted at radio
broadcast towers, and microwaves in microwave ovens. Microwaves are also used to transmit TV and
information signals across Earth and between Earth and satellites. Infrared, visible, and ultraviolet waves are
found in sunlight. X-rays are found in medical laboratories and also are emitted from most stars and galaxies.
Gamma rays are emitted by nuclear reactions in laboratories and in reactors.
DIF: 3
REF: p. 408
OBJ: 27.3
STO: Ph.4.e
33. ANS:
Visible light is transmitted through glass by molecules that do not easily absorb light photons. A light photon
is absorbed for a very short time by a glass molecule, but then it is reemitted in the same direction it was
originally traveling and with the same frequency it originally had. This process continues until the photon
finally emerges from the other side of the glass. Ultraviolet radiation is in the range of frequencies that
resonate with atoms. Glass atoms hold onto UV energy for millions of vibrations, during which time the
energy is passed to neighboring atoms by many collisions. The transmitted energy takes the form of heat
instead of light. So glass is not transparent to ultraviolet radiation.
DIF: 3
REF: p. 409, p. 410
OBJ: 27.4
STO: Ph.4.e, Ph.4.f
34. ANS:
Electric field vectors of an electromagnetic wave vibrate in a plane. When many electromagnetic waves are
present at once, electric field vectors are vibrating in many different planes. A polarizer is a material that
absorbs electromagnetic radiation and passes only radiation that is vibrating in a certain plane. We decrease
the amount of light entering our eyes by using sunglasses that allow only vertically polarized light to pass. A
large fraction of reflected light is horizontally polarized, so sunglasses help reduce glare from reflected light.
DIF: 3
REF: p. 414, p. 415
OBJ: 27.7
STO: Ph.4.b