TPO43托福听力真题解析：Lecture4

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TPO43托福听力解析：Lecture 4

 1. What does the professor mainly discuss?

A.Methods of converting radio waves into sound waves
B.Features of different types of electromagnetic radiation
C.The various paths that very-low-frequency waves follow on Earth
D.The emission and detection of very-low-frequency waves

解析：文章主要是关于低频电磁波的探测和发射过程。选D

2. What is one difference between radio waves and sound waves that the professor emphasizes?

A.Radio waves have a lower frequency.
B.Water stops radio waves from spreading but does not stop sound waves
C.Unlike sound waves, radio waves can travel outside Earth's atmosphere.
D.Naturally occurring radio waves are difficult to detect on Earth at night.

解析：由常识或文章信息可得，电磁波是电磁场的交替震荡，不需要介质传播，而声波依赖介质，无法在外太空的真空中传播。选C

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3. What explanation does the professor give for the constant occurrence of VLF emissions on Earth?

A.At any given time, some part of the world is experiencing sunrise or sunset
B.Wave guides constantly form in the atmosphere.
C.Earth’s magnetosphere directs interplanetary waves toward Earth’s surface.
D.Lightning occurs constantly on the planet.

解析：教授说探测器对闪电发出低频电磁波很敏感，几千公里外的闪电也能探测到，而以几千公里的尺度来说，闪电是经常发生的，故经常可探测，选D。

4. Why are sunrise and sunset the best times to listen to VLF signals?

A.Because thunderstorms are most likely to occur then
B.Because radio waves travel through natural wave guides then
C.Because higher-frequency signals are less active then
D.Because temperatures are not extremely high or low then

解析：教授明确说明了除了金属的wave guide，也有自然的guide，在日升日落的时候。选B

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5. Why does the professor discuss whistlers and tweeks?

A.To illustrate that the path a VLF wave travels can affect the sound it makes on a radio
B.To point out that VLF waves can affect the sounds heard on a household or car radio
C.To describe how a colleague discovered the origin of VLF waves
D.To clarify the difference between VLF waves and other kinds of waves

解析：选A

6. What does the professor imply when he says this:

A.He needs to think before he can answer the woman's question.
B.The woman has underestimated how often VLF waves can be detected.
C.The woman does not realize that waiting for a thunderstorm can take a long time.
D.The woman does not understand the relationship between thunderstorms and lightning.

解析：选B

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