評論
打印
Listen to part of a lecture in a physics class. The Professor has been discussing electromagnetic waves.
請聽物理學課上的部分內容。教授正在討論電磁波。
So are there any questions before we continue our discussion of different types of electromagnetic waves?
在我們繼續討論不同類型的電磁波之前，你們有什么問題嗎？
Um, today, we’ll focus on radio waves, and specifically, very low frequency radio waves. Yes, Tim.
今天我們的重點是無線電波，具體來說是非常低頻的無線電波。Tim，請說。
Are you going to talk at all about the difference between radio waves and sound waves?
你會講無線電波和聲波之間的區別嗎？
Uh, OK.That might be a good place to start actually. Sound waves are mechanical in nature, right?
好的，事實上，這也許是個不錯的切入點。聲波本質上屬于力學，對吧？
It can only originate and spread in places where there’s some dense physical medium, like atmosphere or water.
它只能在有一些密實的物理介質的環境中產生和傳播，比如空氣和水。
They result from changes in pressure in that medium, like changes in air pressure.
它們因那種介質中壓力的變化而產生，比如氣壓的變化。
So they can’t travel through a vacuum, where there is no dense physical medium, which is why they can’t travel through interplanetary space.
所以它們不能在沒有密實物理介質的真空環境中傳播，這也就是為什么它們無法穿過行星間的太空了。
Radio waves, on the other hand, are fundamentally different from sound waves. They are electromagnetic.
而無線電波和聲波有著本質的區別。它們是電磁波。
They result from oscillations of the electromagnetic filed and don’t need a physical medium,
它們從電磁場的振動中產生，不需要物理介質，
