concepts of science ch. 6

What is the velocity of a wave if the distance between the crests is 8 ft and 20 waves go by every 10 seconds?

16 ft/sec

How fast can light travel in one second, if it is moving through a vacuum?

300,000 kilometers

What is the difference between a transverse and a longitudinal wave?

A transverse wave has wave motion perpendicular to the motion of the medium on which the wave moves; for example, pond ripples. A longitudinal wave is a kind of wave in which the motion of the medium is in the same direction as the wave movement; for example, pressure waves or sound waves.

Which statement best describes transverse waves?

A water ripple is a transverse wave.

How do AM and FM radio stations differ in the way they transmit signals?

Amplitude modulation (AM) and frequency modulation (FM) are two different ways that a sound wave can be superimposed on a carrier wave. The carrier wave can be varied (modulated) to carry a signal by altering the amplitude (AM) or its frequency (FM).

What controls the range and pitch of sound in the string section of an orchestra? Compare "string" sounds with the woodwinds and percussion. What do the origin of these sounds have in common? How do they differ?

Answers will vary but should include the length of string and vibration per second; vibration of air, waveform differs.

Extremely low-frequency radiation (ELF) has been in the news since the early 1980s. Discuss this radiation from the point of view of a builder, a scientist, a medical doctor, an EPA bureaucrat and a homeowner living in the shadow of overhead power lines.

Answers will vary. Power company interested in efficiency of lines; scientists measures the field effect; biologist is interested in the affect on organisms; EPA person is interested in risk-benefit analysis; homeowner is concerned about the cheapest mortgage, safety, interpretation of reports.

Discuss the allocation of electromagnetic "real estate" currently controlled by the Federal Communication Commission. What are the positive and negative points of the federal licensing policy?

Answers will vary. The advantage of control is for assignment of safety bands, order out of chaos, taxation, etc. The disadvantages include taxes to company, regulate (quality control imposed), etc.

Discuss the importance of Maxwell's equations. How did his predictions about the electromagnetic spectrum compare with those of the Russian scientist Dimitri Mendeleev, who discovered the periodic table of elements?

Both of models predicted future observations. Both had patterns that could be completed as new technology/equipment was developed

How can destructive interference affect how a person enjoys the music in an auditorium?

Destructive interference may occur when sound waves are reflected from the ceiling or walls of the concert hall and cancel each other out. Some seats in the auditorium may have poor sound quality unless acoustical parameters are considered in the building design.

What is unique about electromagnetic waves? Name several examples.

Electromagnetic waves consist of electric and magnetic fields fluctuating together. These waves move by themselves through the vacuum of space and do not require any medium for transport. Examples can include any waves on the electromagnetic spectrum: X-rays, radio waves, visible light, to name a few.

Gamma rays have long wavelengths and high energy.

False

In Maxwell's equations, the wavelength of radiation can vary but the sum of the wavelength and the wave frequency is always the speed of light.

False

The motion of waves depends upon the source from which they were generated.

False

The sun produces only visible electromagnetic radiation.

False

What is fluorescence?

Fluorescence is a phenomenon in which energy contained in ultraviolet wavelengths is absorbed by the atoms in some materials and then partially emitted as visible light.

What are some practical applications of infrared radiation?

Infrared radiation (also called heat radiation) from the exhaust of enemy aircraft can be detected by military devices and used to guide missiles to their target. Other applications include monitoring hot spots that predict volcanic eruptions and earthquakes and finding heat leaks in homes and businesses.

You've got a toy boat on a pond and want it to go across. If you threw a rock behind the boat to make a wave, would the boat move forward? Why or why not?

No, because waves transfer energy but not mass so there is nothing to push the boat forward.

Identify the materials that will absorb each of the following: radio waves, microwaves, and visible light.

Radio waves can be absorbed by metal; microwaves by water; visible light by the rods and cones in our eyes.

Explain why a rainbow always has the same colors in the same order.

Refraction of light is always the same—therefore the colors are bent in the same manner.

How would the human eye be physically different if it were sense either shorter or longer wavelengths than visible light?

The diameter of pupil would have to be able to close to smaller than a pinpoint for shorter wavelengths; for longer wavelengths, the eye would have to be larger than a meter. Range of frequencies determines the shape and reactivity of the eye.

How is the Doppler effect used in applied technology?

The practical application of the Doppler effect is for police radar units, in which the radar sends out a pulse of electromagnetic radiation that is absorbed by the metal in cars and reemitted, Doppler shifted. The police officers can deduce the speed of a car by comparing the relative speeds of the waves. Similar devices have been designed by meteorologists to tell speed and direction of storms.

Calculate the length of a radio wave picked up by a car radio tuned to 89.3 FM.

The radio wavelength equals the velocity of the radio wave divided by the frequency. In this case, the frequency is 89.3 MHz (8.93 X 107 Hz) and the velocity is the speed of light (3.0 X 108 m/s, for all waves in the electromagnetic spectrum).

Compare the military radar jamming devices with strategies evolved by insects that protect them from bats.

These are basically the same. Both listen for signal then 'chirp' back at the same frequency—sonic camouflage.

Explain how 'noise canceling' headphones might work in a noisy environment.

These headphones use destructive interference to cancel out the noise.

Research has begun to develop a more powerful X-ray source. How will this new tool be applied to problems in society? What principles of electromagnetic radiation are at the foundation of this new research frontier?

These new devices could provide greater penetrating power to look farther or through denser materials for quality control in manufacturing. These excite atoms to high energy levels to get photons to jump to from electron shells to give off x-rays rather than light.

In terms of wave mechanics, what is the nature of the tsunami's destructiveness?

Transfer of energy is dissipated by the shore on which the wave breaks. If structures, plants, animals are on that shore, the energy is transferred to them—as energy is transferred from a train to a car left sitting on the tracks.

Television broadcasts usually split the visual and sound signals, carrying pictures on AM and sound on FM

True

Describe how popcorn pops in a microwave oven.

Water inside the kernel gets energized by the wave, which turns it to steam and causes the kernel to explode.

How are velocity, frequency and length of each wave related?

Wave velocity is equal to the length of each wave times the number of waves that pass by each second.

Do all waves travel at the speed of light? Give examples.

Waves located on the electromagnetic spectrum all travel at the speed of light. These include radio, microwave, infrared, visible light, ultraviolet, X-rays, and gamma rays; none of which require a medium for transport. Waves such as sound waves, seismic waves, and water waves travel much slower than the speed of light.

Which wave does not move in a medium?

X-ray

Sound waves with low frequency

all of the above

What is a practical use of infrared radiation detection

all of the above

Which is associated with radio waves?

all of the above

The ability of microwave ovens to cook food depends partly upon the fact that microwaves

are absorbed quickly by water molecules.

Constructive interference is to destructive interference as

b & c b. a + a is to (+a) + (-a). c. rough is to smooth.

If you are standing in the path of a light moving toward you, the Doppler effect predicts that the light will be

blue shifted.

The fundamental difference between electromagnetic waves and other types of waves is that electromagnetic waves

can transfer energy without transferring mass.

The Doppler effect

describes sound wave frequency from a moving source.

A light wave propagates itself through

energy in shifting magnetic and electric fields

Low frequency sound waves have high pitches.

false

Nocturnal animals have learned to use microwave radiation.

false

The radio waves on the electromagnetic spectrum have the shortest wavelengths and the highest energy.

false

Visible light occupies the majority of the electromagnetic spectrum.

false

You can't see all wavelengths but you can hear all wavelengths.

false

Compared to microwave radiation, infrared radiation

has shorter wavelengths and higher energy.

Albert Michelson was the first U.S. scientist to win the Nobel Prize for

his studies of light.

Bats navigate by emitting high pitched sound waves and

listening for an echo.

Light passing through a window is like

radio waves passing through the air.

Which waves are outside the range of a human's ability to detect?

sound waves with frequencies less than 20 Hz

Which is the same for all types of electromagnetic waves?

speed

Which of the following is the same for all kinds of electromagnetic waves?

speed

The frequency of a wave appears to change if there is motion between the wave source and the observer. This phenomenon is known as

the Doppler effect.

What causes an electromagnetic wave to be emitted?

the acceleration of an electric charge

You are riding in your car during a thunderstorm listening to the radio. A bold of lightning strikes a few miles distance; you see the bolt and a few seconds later hear the thunder. However, the radio speaker made a "pop" sound just as the lightning bolt struck. How did the ratio 'hear the thunder' before your ears did?

the lightning produced a radio frequency

Which of the following is associated with 440 Hz?

the tuning of a musical instrument to middle A

What practical use has been found for gamma rays?

treating cancerous tissues

A wave carries energy but not matter across an intervening distance.

true

All waves on the electromagnetic spectrum are the result of an accelerating electric charge.

true

An electromagnetic wave can travel through a vacuum.

true

In both longitudinal and transverse waves, the energy always moves in the direction of the wave.

true

The AM radio stations can be heard over greater distances because frequencies between 530 and 1600 MHz are partially reflected off the layers of the atmosphere.

true

The Doppler effect describes a higher pitch sound for waves approaching an observer and a lower pitch sound for waves moving away from an observer.

true

The human eye can distinguish many wavelengths of red and blue, but only a few wavelengths of yellow.

true

Your body produces electromagnetic radiation while you are taking this exam.

true

Which electromagnetic frequencies are used to irradiate fruit to kill the pests and their eggs that might be on the fruit?

ultraviolet

Which radiation can be used to sterilize equipment?

ultraviolet radiation