Deck 12: Electromagnetic Waves

Question 1

Radio waves travel through empty space

A) Faster than visible light
B) Slower than visible light
C) At the speed of visible light
D) With only electric fields and not magnetic fields

Answer 1

At the speed of visible light

Question 2

Imagine being an observer watching a light wave travel by you, much like you would watch a car travel by you on the highway. If you could detect the electric field at your location, you would observe

A) the electric field remaining constant because light does not carry charge.
B) the electric field undulating to the right or left as the wave travels to the right or left.
C) the electric field undulating up and down as the wave travels to the right or left.
D) no electric field at all.

Answer 2

the electric field undulating up and down as the wave travels to the right or left.

Question 3

The speed of light is about

A) 299 million miles per hour.
B) 299 million kilometers per hour.
C) 299 million meters per second.
D) 299 thousand meters per second.

Answer 3

299 million meters per second.

Question 4

The speed of light is roughly 300,000,000 m/s. A radio station has frequency 100 megahertz. What is the station's wavelength?

A) 30,000,000,000 meters
B) 3,000,000 meters
C) 3.0 meters
D) 0.33 meters

Question 5

What type of circuit is used to tune a radio?

A) Radio circuit
B) Antenna circuit
C) Tank circuit
D) Inductance circuit

Question 6

If an electric field wave oscillates north and south, and the wave is traveling straight up, then what direction does the magnetic field wave oscillate?

A) East and west
B) North and south
C) Up and down
D) It does not oscillate: this situation is impossible.

Question 7

What does "AM" stand for?

A) AMplification
B) Antenna Modulation
C) Antenna Modification
D) Amplitude Modulation

Question 8

Why does FM radio sound richer than AM radio?

A) FM is higher frequency.
B) FM electronics produce better sound reproduction.
C) FM has a larger bandwidth.
D) FM antennas need not be as tall as AM antennas.

Question 9

A typical bandwidth for an FM radio station is

A) 100 kHz
B) 200 kHz
C) 100 MHz
D) 200 MHz

Question 10

An engineer at the company you are working for has just reported finding an unusual electromagnetic wave. This wave consists only of an electric field, with no magnetic field accompanying it. You are certain that the engineer is mistaken because

A) an electromagnetic wave must have a magnetic field that changes with time to produce its electric field.
B) electromagnetic waves always contain both electric charges and magnetic poles, and magnetic poles are accompanied by magnetic fields.
C) electromagnetic waves contain moving electric charges and charges produce magnetic fields when they move.
D) while waves consisting only of electric fields are common and travels indefinitely through space, they are known as "electric waves," not "electromagnetic waves."

Question 11

An FM radio station instructs your radio receiver how to move its speaker cone by varying the

A) amount of electric charge it pushes up and down its antenna.
B) amplitude of the radio wave it produces.
C) strength of the electric and magnetic fields in the radio wave it produces.
D) frequency of the radio wave it produces.

Question 12

A tank circuit

A) switches energy stored between electric in the capacitor and magnetic in the resistor.
B) switches energy stored between electric in the inductor and magnetic in the capacitor.
C) switches energy stored between electric in the capacitor and magnetic in the inductor.
D) switches energy stored between electric in the resistor and magnetic in the inductor.

Question 13

Suppose you could see AM and FM radio signals - you could perceive brightness and color. Describe how these two radio signals would appear to your eye.

Question 14

You are a scientist and you announce that you have discovered a new form of electromagnetic radiation which has wavelengths much shorter than visible light. Please describe three properties your new waves must have.

Question 15

A radio tuner works because

A) the charge sloshes back and forth in the tank circuit at a certain frequency and the station being tuned in to must be very near that frequency.
B) the capacitor dimensions must be the same size as the signal wavelength.
C) the magnetic field in the inductor must be the same size as that of the signal.
D) the electric field in the capacitor must be the same size as that of the radio signal.

Question 16

One way radio waves do not differ from visible light is that

A) There will never be a movie named "Visible Light".
B) Radio waves have less energy and travel slower than visible light.
C) Radio waves have less energy and travel faster than visible light.
D) Radio waves travel at the same speed as visible light.

Question 17

Radio waves are similar to visible light in that

A) both travel at the same speed in a vacuum.
B) both have wavelengths longer than ultraviolet light.
C) A and B
D) both have wavelengths shorter than X - Rays

Question 18

In their closing statement, an attorney at the company you are working for has just reported finding an unusual electromagnetic wave. This wave consists only of an electric and magnetic fields which are constant in time and do not vary. You are certain that the attorney is mistaken because

A) an electromagnetic wave must have fields that change with time to produce each other.
B) electromagnetic waves are mainly electric.
C) electromagnetic waves are mainly magnetic.
D) there needs to be a charge somewhere in order to have an electric field.

Question 19

Please sketch examples of AM and FM signals, discussing two important differences between the waves.

Question 20

Which of the following would not be likely to cause an FM radio signal to cut out?

A) tall buildings
B) driving over pronounced hills
C) fog and rain
D) being inside a metal room

Question 21

Electric fields come from

A) electric charge only.
B) electric charge or changing magnetic fields.
C) changing magnetic fields only.
D) electric charge or any magnetic field.

Question 22

Magnetic fields come from

A) electric current only.
B) electric current or any electric field.
C) changing electric fields only.
D) electric current or changing magnetic fields.

Question 23

Microwaves have wavelengths between

A) 1 micron to 100 microns.
B) 1 millimeter to 1 meter.
C) 1 micrometer to 1 millimeter.
D) 1 meter to 1000 meters.

Question 24

Microwaves have

A) shorter wavelengths than visible light
B) comparable wavelengths to visible light
C) longer wavelengths than visible light
D) no wavelength at all

Question 25

Microwaves have

A) lower frequencies than visible light
B) comparable frequencies to visible light
C) higher frequencies than visible light
D) no frequency at all

Question 26

There is a metal screen on the front window of a microwave oven. This screen is essential because it

A) prevents electric charge from accumulating on the window.
B) protects the window from splatters that may occur when food inside the oven boils.
C) reflects microwaves and keeps them inside the oven.
D) prevents the glass from breaking in response to the rapid heating of its inner surface and the thermal stresses that result.

Question 27

A compact disc contains an extremely thin sheet of aluminum. If you put a larger block of metal in a microwave oven along with a CD and turn the oven on,

A) nothing significant happens.
B) only the metal will spark and then melt.
C) the metal will melt and the CD will spark.
D) only the CD becomes hot enough to soften and sparks dance about its surface..

Question 28

If you put an egg in a microwave oven, it will become very hot. But if you put a dehydrated egg (a dried egg containing no water) in the microwave oven, the egg will not be affected because

A) the dehydrated egg is too dry to have a temperature. Only foods containing water or oil can actually become hot.
B) the dehydrated egg reflects the microwaves while the normal egg does not.
C) microwaves transfer heat to food principally through its water molecules.
D) the dehydrated egg is much less dense than a normal egg and doesn't conduct heat well.

Question 29

Compared to the radio waves used in normal radio broadcasts, the microwaves used for satellite transmissions have

A) higher frequencies and shorter wavelengths.
B) higher frequencies and longer wavelengths.
C) lower frequencies and shorter wavelengths.
D) lower frequencies and longer wavelengths.

Question 30

Microwaves can't get through the metal screen in a microwave oven, but light can because

A) light travels faster than microwaves.
B) the wavelength of visible light is about the same size as the holes.
C) the wavelength of microwaves is about the same size as the holes.
D) the screen acts like a resistor, absorbing the microwaves and not reflecting them.

Question 31

There is a microwave oven in use, which is inside a tightly - sealed metal - lined room, with the door shut. A person with a pacemaker claims that when she walked by the room, microwaves leaked out through the metal and damaged their pacemaker. Please comment on the scientific validity of their claim.

Question 32

We have discussed how microwaves behave inside the cavity of a microwave oven. Suppose you had special vision so that the microwaves inside the oven were visible to you when it is turned on. What would the inside of the oven look like? Here you can assume that the oven creates and uses microwaves at only one frequency.

Question 33

Explain why a CD placed in a running microwave oven sparks.

Question 34

Describe the two types of uneven cooking encountered in microwave ovens.

Question 35

Microwaves have speeds

A) greater than visible light.
B) less than visible light.
C) equal to visible light.
D) 55 miles per hour; it's still the law.

Question 36

When electrons circle in a magnetic field they are exhibiting

A) juvenile behavior.
B) cyclotron motion.
C) cycling motion.
D) motion at constant velocity.

Question 37

Compared to the radio waves used in normal radio broadcasts, visible light has

A) higher frequencies and shorter wavelengths.
B) higher frequencies and longer wavelengths.
C) lower frequencies and shorter wavelengths.
D) lower frequencies and longer wavelengths.

Question 38

Types of light that can get through the screen on a microwave oven are

A) anything with wavelengths longer than microwaves.
B) anything with wavelength about the same size as the holes.
C) ultraviolet and X-ray.
D) all radio and X-ray.

Question 39

You just got pulled over and want to distract the police officer into forgetting how fast you were traveling. You ask them "how can a microwave oven have electric fields inside its metal cavity but no net charge on the cavity?" Aside from personal feelings, how should the officer respond scientifically?

Question 40

Suppose you are hired by a microwave company and you quit in anger. To punish them, during your last week you make the ovens with magnetrons slightly smaller or bigger than the stock ones. What effect will this have on the ovens?