Name: 微波爐加熱葡萄如何製造等離子體？ (How Microwaving Grapes Makes Plasma)
Uploaded: 2021-01-14T10:25:38.000Z
Duration: 8 min 16 s

almost eight years ago when this channel was fresh and before I had gray hairs in

大概八年前這個頻道還很新的時候 在我的鬍子有白髮之前

my beard in fact before I had a beard I made a video showing that if you take a

事實上，在我留鬍子之前我製作了一個影片

grape and cut it almost completely in half and put it in the microwave you can

如果你拿一顆葡萄，把它完整切半 然後把它放在微波爐裡

but the explanation we had in that video was lacking this was

但在那影片中，我們缺少了解釋

me and my friend Dr. Stephen Bosi a fellow physicist so you should look

這是我 和 我的朋友Stephen Bosi博士 一位物理學家

forward to that on another episode of veritasium to be honest nobody really

"你應該期待veritasium頻道的續集"

knew how this effect worked that is until now as of the publication of this

說實話沒人真的知道這種效應是如何起作用的

video three scientists have published an explanation in the Proceedings of the

National Academy of Sciences they studied this effect with high-speed

cameras thermal cameras electromagnetic modeling and they came up with an

三位科學家在"美國國家科學院院刊"(PNAS) 發表文章解釋

explanation that I think is pretty satisfying and it extends way beyond

他們研究這個效應，用高速攝影機、熱顯像攝影機

just microwave great plasma so naturally I called up these scientists yeah

actually saw your video before that your videos before joining the grape project

他們想出一個我覺得很令人滿意的解釋

oh really that's why I was like already kind of

他遠遠超越，不單只是微波、明顯的電漿

like interested before joining the project the scientists showed you don't

因此自然地，我跟這些科學家們通了電話

even need to use a grape you can get the same effect with hydrogel water beads

事實上在那之前看過你的影片 加入葡萄項目之前看過影片

these are those tiny polymer beads which when you soak in water they increase in

這就是為什麼我在加入這個項目之前就已經有點興趣了

to understand how microwaving a grape gives you plasma we first need to know a

科學家們表示甚至你不需要用到一顆葡萄

few things like a typical household microwave uses a frequency of

你可以從"水凝膠水珠"得到相同的效果

electromagnetic radiation at about two point four five gigahertz that means

that the wavelength of microwaves inside the oven is about twelve centimeters

當你把它浸泡在水中時，它們體積會增加100倍

long. now if you've ever studied electromagnetic radiation you might have

為了了解微波一顆葡萄如何產生電漿

the intuition that interesting things start to happen when the object or

obstacle is around the same size as the wavelength which a grape certainly is not

像是一台典型的家用微波爐 使用的電磁輻射頻率

it's not twelve centimeters but the important quantity is how big is the

wavelength inside the object inside the grape twelve centimeters in air but the

這表示在爐內微波的波長大約是12cm長

like index of refraction of grape material must be close to like one point

現在，如果你曾經學過電磁輻射

three three or something right like at visible wavelengths it is a lot lower

你可能有個直覺，有趣的事情將發生

but in the microwave regime the index of refraction is a almost 10 so you have a

當物體或障礙物與波長大約在相同尺寸時

much higher index of refraction so microwaves are traveling you know like

ten times slower through the grape than they are through yet air yes and that

means that the wavelength is a tenth its size through air so instead of twelve

在物體內部、葡萄內部的波長  有多大

centimeters it's about 1.2 centimeters right about the size of a grape now if

you take a single grape and place it inside the microwave don't cut it in

但，像葡萄之類的材料 折射率應該接近1.33

half what you find is that the microwaves actually become trapped

"是的，像在可見光波長低許多"

inside the grape and that's because of its high refractive index and its size

但在微波頻段折射率幾乎達到10

because turns out that when you have like a ball where approximately the

所以你有一個高得許多的折射率

diameter is roughly the same as the wavelength of the microwaves in the material. It

所以微波在葡萄裡行進 比在空氣中慢了十倍  "是的"

actually turns out that it can be trapped in there so that it interacts its kind...

這表示波長只有空氣中的1/10，所以不是12cm

it's kind of it bounces at the borders of the of the ball and it can't get out

is it like total internal reflection? yes pretty much wow that's interesting I

hadn't thought of it that way so the microwaves become trapped inside

現在你拿單一顆葡萄放進微波爐 不要切半

the grape and they actually form these resonant modes you can think of them as

你會發現微波實際上被困在葡萄內部

standing waves just ways in which the electromagnetic fields like to

oscillate inside a grape such that the maximum electromagnetic field is

actually in the center of the grape when you put in the microwave you see that it

heats up not from the outside in like you would expect if it was just

absorbing the microwaves but rather from the inside out. if you add a second grape

它相互作用...它有點像在球的邊緣反彈，跑不出去

to the microwave you see that the same thing happens the microwaves get trapped

這像是全內反射嗎？ "是，差不多"

in the second grape too- and the amplitude is highest in the very center of the

grape and so the heating occurs most of all of there. but if you move these two

grapes close together so they're closer than say a wavelength well then you can

他們實際上形成了這些共振模式

start to get interactions between the electromagnetic fields in the one grape

你可以把它們想成是駐波 就是電磁場偏好在葡萄內部震盪

and in the other and in fact if you get the grapes touching then the greatest

如此，最大的電磁場強度將落在葡萄的中心

electromagnetic field actually occurs at that contact point between the two

grapes and so that is where you're gonna get the greatest oscillating

你會看到加熱過程  不是你預期的從外而內的吸收微波

electromagnetic fields and that is where those grapes are going to get hottest

it's also interesting that you don't need to cut the grapes in half. two

如果你放入第二顆葡萄到微波爐 你會看到一樣的事情發生

grapes placed side-by-side will make this effect work as long as they stay in

contact. but that's why in a lot of the videos you see there's a watch glass so

the reason the watch glass is there is to keep the grapes together now

with the very strong electromagnetic fields at the intersection of the two

但如果你讓這兩個葡萄靠得很近

grapes what you can get is some sparks some breakdown of air that is the

所以它們靠得  比一個波長還短

electric fields are strong enough that they ionize the air creating those

你可以開始看到一個葡萄的電磁場與另一個之間的互動

Sparks and that is what leads to the plasma it creates these ions which can

then receive more energy from the microwaves. you can see it here pulsing

最大的電磁場實際上會發生在這兩個葡萄之間的接觸點

at 120 Hertz that's twice the 60 Hertz frequency of mains power which reflects

所以這就是你會得到最大電磁場震盪的地方

the fact that the amplitude of the microwaves is pulsing twice every cycle

and what is that plasma made of? well the scientists looked at the spectrum of the

這也很有趣，你不用將葡萄切成兩半

plasma from a grape and they found that there's a strong potassium emission line

並排放置的葡萄，只要保持接觸，這種效果就會起作用

and also a sodium emission line so it seems like those ions must be pretty

這就是為什麼在很多影片裡會看到手錶玻璃

common in the grape and when the plasma gets formed as those ions which are

原因是手錶玻璃可以讓葡萄保持接觸

sprayed up into the air and that is what we're seeing

伴隨著非常強的電磁場在兩個葡萄間的交錯點

who needs drugs?! now the size of the grapes is important which is something I

你能得到的是空氣中的一些火花、一些崩解

of course suspected because you don't see this happening with too many other

這是電場足夠強大，將空氣電離產生這些火花

squishy fruits but you don't have to get them the exact right size and this is

致使產生電漿的，是創造了這些離子後

because water absorbs microwaves so the scientists did some modeling of this and

if you had a material inside the grape that did not absorb microwaves then what

你可以看到有個120Hz的脈衝，那是60 Hz主電源的兩倍

you would see is at certain particular sizes you get extreme amplification of

反映出一個事實，微波震幅每個週期都會發出兩次脈衝

the electromagnetic fields it's basically one size that you'd have to

hit to get the amplification but made of an absorbent material like water this

科學家研究了從葡萄產生的電漿的光譜

broadens out the peaks so you get less amplification of the field but over a

broader range of sizes this is why a lot of grapes will work even if the sizes

vary. so in terms of like applications of this research what do you think I mean

所以似乎這些離子是常見於葡萄

obviously people like me are excited and because this is a fun trick but but

且當電漿形成、這些離子被噴到空氣中 這就是我們所看到的

beyond that what do you think in terms of like applications of this? the main

limit in fabricating microchips right now and going smaller and smaller is the

lithography so how to make these very small features. this phenomenon shows

當然有所懷疑  因為你在其他很多濕軟的水果看不到效果

that two spheres of the right size and refractive index can focus

electromagnetic energy down to a tiny spot in between them in this case down

to around a millimeter from radiation with a 12 centimeter wave length if

similar focusing could be achieved with light it would provide a significant

如果你在葡萄裡面有一種材質   並不吸收微波

improvement over current lithography techniques. So if we could somehow harness

你會看到在特定的尺寸 有著極大的電磁場放大效果

this to do this lithography to be able to maybe write things very small you

could actually use light to to make really small features you could do like

every two nanometers marks spot with about 2 nanometers resolution - it would help

但是，像水這樣的吸收材料，會擴大峰值

help continue this like Moore's Law yes it would help continue Moore's Law like

得到較少的放大效果 但是適用的尺寸範圍更廣了

putting much more small things in a single chip so I'm glad I was finally able to

這就是為什麼很多葡萄都可以起作用  即使尺寸有變化