Chapter 8: Electromagnetism and EM Waves
TRUE/FALSE
1. The deviation from the way a compass needle points from the true north direction is the
magnetic declination.
2. The direction of a magnetic field at a point can be determined by a compass.
3. There are positive and negative magnetic charges, analogous to positive and negative
electric charges.
4. A stationary electric charge produces a magnetic field around it.
5. Moving electric charges make magnetic fields.
6. The shape of the magnetic field around a bar magnet is very close to the shape of the electric
field around a single positive charge.
7. One can reverse the north and south poles of an electromagnet by reversing the direction of
current flow through it.
8. Three devices that use electromagnetic induction in their operation are generators,
transformers, and dynamic microphones.
9. A transformer only works with AC.
10. A speaker can be used as a crude microphone.
11. An electric motor can be manually turned and made to act as a generator.
12.
The ionosphere reflects high frequency radio waves.
13. The ozone layer absorbs infrared radiation from sunlight.
14. The greenhouse effect occurs because carbon dioxide in the atmosphere absorbs ultraviolet
radiation.
15. The increase in the amount of carbon dioxide in the atmosphere is responsible for the
greenhouse effect.
16. The frequency of visible light determines its color.
17. The main form of radiation that our bodies emit is ultraviolet.
18. Blackbody radiation is emitted from a small hole in a furnace.
19. X rays are used in radar.
20. Bones show up in x ray images because they absorb x rays more efficiently than muscle and
other tissues do.
21. Gamma radiation is the highest frequency of EM waves.
22. EM waves travel at a speed that varies with their wavelength.
23. Infrared radiation causes your skin to tan.
24. Blue light has a longer wavelength than red light.
25. Gamma rays are emitted when high speed electrons decelerate as they are smashed into a
metal target.
26. The wavelength of a radio wave from an AM station broadcasting at 1,000 kilohertz on your
radio dial is 300 meters.
27. The wavelength of a radio wave from an FM station broadcasting at 93.9 megahertz on your
radio dial is 0.313 meters.
28. The cosmic background radiation corresponds to a blackbody at a temperature of 2.726
kelvins.
29. A changing magnetic field produces an electric field.
30. If the Kelvin temperature of an object is doubled, the amount of radiant energy emitted each
second is twice the original amount.
31. As the temperature of an object increases, the wavelength of the brightest light emitted
increases.
32. If the Kelvin temperature of a body is doubled, the wavelength of the most intense light is
double the wavelength originally of the most intense light.
33. As the temperature of a body increases the color of the body shifts from blue to red.
34. The peak of a body’s blackbody radiation curve shifts toward longer wavelength as the
temperature of the body increases.
35. The peak of a body’s blackbody radiation curve shifts upward as the temperature of the
body increases.
36. A body in a room at 300 K is heated to 3,000 K. The amount of energy radiated each second
by the body increases 10,000 times.
37. A body in a room at 300 K is heated to 3,000 K. The wavelength of the most intense EM
radiation emitted by the body at 3,000 K is 10 times the wavelength of the most intense EM
radiation at 300 K.
38. A coil of wire is connected to a galvanometer. When a bar magnet is moved in and out of
the coil, the galvanometer records a current because of electromagnetic induction.
39. A coil of wire is connected to a galvanometer. When the coil is rotated in a magnetic field,
the galvanometer records a current because the free electrons in the moving wire experience
a force from the magnetic field that pushes them through the wire.
40. AM radio stations have greater range than FM stations because they have more powerful
transmitters.
41. N rays do not exist.
42. The magnetic compass in an aircraft point to the geographic north pole.
43. Higher frequency radio waves are reflected by the ionosphere.
44. The ionosphere can be used to conduct radio communications over long distances.
45. Thermograms use ultraviolet radiation to sense heat.
MULTIPLE CHOICE
1. The deviation from the way a compass needle points from the true north direction is the
a.
greenhouse effect
b.
magnetic inclination
c.
magnetic declination
d.
magnetic resonance effect
e.
none of the above
2. The direction of a magnetic field at a point can be determined by
a.
a generator
b.
a compass
c.
a transformer
d.
electromagnetic induction
e.
none of the above
3. A magnetic field exerts a force on an electric charge if the charge is
a.
positive
b.
negative
c.
moving
d.
stationary
e.
any of the above
4. A magnetic field is created by an electric charge if the charge is
a.
positive
b.
negative
c.
moving
d.
stationary
e.
any of the above
5. An iron nail is brought near a magnet. Which of these is not true?
a.
The nail has a north pole and a south pole.
b.
The nail becomes a north pole or a south pole.
c.
The magnet exerts an attractive force on the nail.
d.
The nail exerts an attractive force on the magnet.
e.
The nail is ferromagnetic.
6. Electromagnetic induction is used in the operation of
a.
generators
b.
transformers
c.
dynamic microphones
d.
regenerative braking
e.
all of the above
7. The ionosphere
a.
reflects all EM waves
b.
reflects high frequency radio waves
c.
reflects low frequency radio waves
d.
is responsible for the greenhouse effect
e.
absorbs ultraviolet light in sunlight
8. The ozone layer
a.
reflects all EM waves
b.
reflects high frequency radio waves
c.
reflects low frequency radio waves
d.
is responsible for the greenhouse effect
e.
absorbs ultraviolet light in sunlight
9. The greenhouse effect occurs because
a.
low frequency EM waves are reflected from the atmosphere
b.
high frequency EM waves are reflected from the atmosphere
c.
the ozone layer absorbs ultraviolet light
d.
carbon dioxide in the atmosphere absorbs infrared radiation
e.
none of the above
10. The greenhouse effect is occurring because
a.
the ozone layer is being depleted
b.
the amount of carbon dioxide in the atmosphere is increasing
c.
the ionosphere reflects low frequency radiation
d.
more ultraviolet radiation is penetrating the atmosphere
e.
none of the above
11. Of the following gases, which is the most important contributor to the Earth’s greenhouse
effect?
a.
water vapor
c.
CFCs
b.
ozone
d.
methane
12. A superconductor expels any magnetic field from its interior. This is called
a.
electromagnetic induction
b.
Maxwell’s effect
c.
magnetic declination
d.
the Meissner effect
e.
none of the above
13. The main form of radiation that our bodies emit is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
blackbody
14. The radiation emitted from a small hole in a furnace is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
blackbody
15. The type of EM waves used in radar is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
blackbody
16. The type of EM wave having the highest frequency is
a.
ultraviolet
b.
infrared
c.
x rays
d.
microwave
e.
gamma rays
17. The EM wave that has the lowest frequency in this list is
a.
ultraviolet
b.
infrared
c.
x rays
d.
microwave
e.
gamma rays
18. The lowest frequency visible light is
a.
violet
b.
red
c.
blue
d.
green
e.
yellow
19. The highest frequency visible light is
a.
violet
b.
red
c.
blue
d.
green
e.
yellow
20. Which of the following is not a common use of microwaves?
a.
cooking
c.
radar
b.
medical imaging
d.
communications
21. How do microwave ovens can heat food more quickly than conventional ovens?
a.
Microwaves give energy directly to the molecules in the food.
b.
Conventional ovens must conduct heat from the surface to the interior of the food.
c.
Microwaves heat the inside as well as the surface of the food.
d.
all of the above
22. The EM wave that has the smallest wavelength in this list is
a.
ultraviolet
b.
infrared
c.
x rays
d.
microwave
e.
gamma rays
23. The type of EM radiation that causes your skin to tan is
a.
ultraviolet
b.
infrared
c.
x rays
d.
microwave
e.
gamma rays
24. FM radio only operates in the frequency range 88 MHz to 108 MHz because
a.
higher or lower frequencies are blocked by the ionosphere
b.
higher and lower frequencies are not radio waves
c.
the government set those limits
d.
none of the above
25. Why would a decrease in the amount of ozone in the atmosphere increase the likelihood of
people getting sunburn?
a.
Global temperatures would rise
b.
More ultraviolet radiation would reach the ground
c.
People would be exposed to more infrared radiation
d.
The premise is incorrect. Ozone and sunburn are not related
26. The type of EM radiation emitted when high speed electrons decelerate as they are smashed
into a metal target is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
gamma ray
27. The type of EM radiation that has wavelength just a bit shorter than that of visible light is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
gamma ray
28. The type of EM radiation that has wavelength just a bit longer than that of visible light is
a.
ultraviolet
b.
infrared
c.
x ray
d.
microwave
e.
gamma ray
29. The wavelength from an FM station broadcasting at 93.9 megahertz on your radio is
a.
31.3 m
b.
3.13 m
c.
0.313 m
d.
0.0313 m
e.
none of the above
30. AM radio stations have greater range than FM stations because
a.
AM is more efficient than FM
b.
they have more powerful transmitters
c.
their lower frequency radio waves reflect off the ionosphere
d.
none of the above
31. What’s the Big Bang?
a.
the creation of the universe
b.
microwave radiation from all directions in the sky
c.
the Hubble relation
d.
a punk rock band
32. Global warming
a.
has not yet been observed
b.
has been caused by increasing levels of carbon dioxide in the atmosphere
c.
has led to a depletion of the ozone layer in the atmosphere
d.
has no serious consequences
33. If the Kelvin temperature of an object is doubled, the amount of radiant energy emitted each
second is ____________ the original amount.
a.
1/16th
b.
half
c.
the same as
d.
2 times
e.
16 times
34. As the temperature of an object increases, the wavelength of the brightest light emitted
a.
increases
b.
decreases
c.
doesn’t change
d.
depends on the composition of the body
e.
depends on the size of the body
35. If the Kelvin temperature of a body is doubled, the wavelength of the most intense light is
____________ the wavelength originally of the most intense light.
a.
1/16th
b.
half
c.
the same as
d.
2 times
e.
16 times
36. As the temperature of a body increases,
a.
the body gets brighter
b.
the color of the body shifts from red to white