Today we are going to be talking about polarisation.

今天，我們將討論兩極分化問題。

Now what does it mean for a wave to be plane polarised?

那麼，波的平面偏振是什麼意思呢？

A wave is plane polarised if the particles or the electromagnetic field oscillate in a single plane only.

如果粒子或電磁場只在一個平面內振盪，那麼波就是平面極化的。

And this is a property of transverse waves.

這是橫波的特性。

So both of these aspects are very important for this definition.

是以，這兩方面對於這個定義都非常重要。

Let me illustrate this.

讓我來說明一下。

For instance, you could have a piece of string.

例如，你可以有一根繩子。

That piece of string could be oscillated in multiple different directions.

那根繩子可以在多個不同的方向上擺動。

For instance, we could choose to oscillate this in the vertical plane, like so.

例如，我們可以選擇在垂直面上擺動，就像這樣。

So each of those particles are going to be moving up or down along here.

是以，每個粒子都會沿著這裡向上或向下移動。

So each of them is going to be going up or down, up or down, up or down.

是以，它們中的每一個都會上升或下降，上升或下降，上升或下降。

However, we can also choose to oscillate this piece of string in the horizontal plane as well.

不過，我們也可以選擇在水準面上擺動這根繩子。

In that case, the particles are going to be moving horizontally along this plane, like so.

在這種情況下，粒子將沿著這個平面水準移動，就像這樣。

And a wave is said to be plane polarised if the particles oscillate in a single plane.

如果粒子在一個平面內振盪，則稱該波為平面極化波。

Let's have a look at a few conventions for denoting some different types of polarisation.

讓我們來看看幾種表示不同類型極化的慣例。

Let's start off with some unpolarised waves.

讓我們從一些非極化波開始。

For instance, sunlight tends to be unpolarised.

例如，陽光往往是非極性的。

So this means that the electromagnetic field is oscillating in many different planes.

這意味著電磁場在許多不同的平面上振盪。

Some of it is going to be in the horizontal plane, some of it is going to be in the vertical plane.

其中有些會在水平面內，有些會在垂直面內。

And this is denoted with the following symbol.

並用以下符號表示。

So essentially it's a cross with denoting that the particles are moving both up and down.

是以，從本質上講，它是一個十字架，表示粒子在上下運動。

They have a component moving up and down, a vertical component.

它們有一個上下移動的部分，即垂直部分。

And they also have a horizontal component, which denotes that the particles or the electromagnetic field will be moving horizontally as well, or a mixture of all of them.

此外，它們還有一個水準分量，表示粒子或電磁場也在水準方向上移動，或者是它們的混合體。

If the particles or the EM waves are polarised in the vertical plane, we often denote this simply with an arrow moving up and down, like so.

如果粒子或電磁波在垂直面上偏振，我們通常會用一個上下移動的箭頭來表示，就像這樣。

And if it's horizontally plane polarised, we can also denote this with a horizontal arrow to show that the electromagnetic field or the particles are oscillating in the horizontal direction.

如果是水平面極化，我們還可以用一個水準箭頭來表示，說明電磁場或粒子在水準方向上振盪。

OK, guys, well, let's have a look at how this works in terms of polarising filters.

好了，夥計們，讓我們來看看偏振濾光鏡是如何工作的。

Let's imagine that we have some unpolarised light, for instance, and we can see that the EM wave is oscillating in both planes in this case.

讓我們想象一下，比如說，我們有一些未偏振的光，在這種情況下，我們可以看到電磁波在兩個平面上振盪。

As soon as it reaches what is known as a polarising filter, the component which is oscillating in the horizontal direction will be absorbed and only light which is oscillating in the vertical plane will pass through the polarising filter.

當光線到達所謂的偏振濾光器時，在水準方向上擺動的部分將被吸收，只有在垂直面上擺動的光線才能通過偏振濾光器。

So this means that the light will look like this as it emerges out of the polariser.

是以，這意味著光線從偏振鏡出來時會是這樣的。

OK, guys, now let's add a second polarising filter.

好了，夥計們，現在讓我們添加第二個偏振濾鏡。

And let's make sure that we rotate the second polarising filter at 90 degrees to the first one.

確保第二個偏振濾光鏡與第一個偏振濾光鏡成 90 度旋轉。

So the first one, you can see it had a vertical orientation and this one has a horizontal orientation.

是以，你可以看到第一個是垂直方向，而這個是水準方向。

In this case, light which is vertically polarised will be absorbed.

在這種情況下，垂直偏振光會被吸收。

So this means that no light is going to go through as there's no component oscillating in the horizontal plane and the second filter will only let light through which is oscillating in the horizontal plane.

是以，這意味著沒有光線會通過，因為水準面上沒有擺動的分量，而第二個濾波器只會讓在水準面上擺動的光線通過。

OK, guys, so hopefully you've enjoyed my explanation of polarisation.

好了，夥計們，希望你們喜歡我對極化的解釋。

Thank you very much for watching and I'm going to see you in the next video.

非常感謝您的收看，我們下期視頻再見。