Why can't you put metal in a microwave? - Aaron Slepkov

譯者: 麗玲 辛 審譯者: Helen Chang

American engineer Percy Spencer developed World War II RADAR technology

美國工程師珀西·史賓塞 開發了二戰雷達技術，

that helped detect Nazi airplanes—

幫助偵測納粹飛機，

but it would soon have other surprising applications.

很快也發現了其他驚人的用途。

One day in 1945, Spencer was standing near a RADAR instrument

1945 年的某天，史賓塞站在一台 名為磁控管的雷達儀器附近，

called a magnetron,

a device that produced high-intensity microwaves that could reflect off planes.

這個裝置能產生高強度微波， 會被飛機反射。

Suddenly, he noticed that the candy bar in his pocket had melted.

突然，他注意到 口袋裡的巧克力棒融化了。

He exposed other things to the magnetron and, sure enough,

他將其他物品靠近磁控管，

popcorn kernels popped,

果然，爆米花粒爆開，

and an egg—well— exploded onto a colleague.

雞蛋也爆裂，噴到一位同事身上。

Soon after, the first microwave oven became available,

不久後，第一台微波爐問世，

operating using the very same technology.

就採用了同樣的技術。

So, how does it work?

那麼，它是怎麼運作的呢？

All light energy travels in waves of oscillating electric and magnetic fields.

所有光能都以振盪的電場 和磁場的形式傳播。

These oscillations span a range of frequencies

這些振盪涵蓋了電磁波的頻率範圍。

comprising the electromagnetic spectrum.

The higher the frequency, the more energetic.

頻率越高，能量越強。

Gamma rays and X-rays have the highest frequencies;

伽瑪射線和 X 射線的頻率最高；

microwaves and radio waves, the lowest.

微波和無線電波則是最低。

Generally, light’s oscillating electric field exerts forces on charged particles,

一般來說，光的振盪電場 會對帶電粒子產生作用，

like the electrons in a molecule.

就像分子中的電子一樣。

When light encounters polar molecules, like water,

當光遇到水等極性分子（例如水）時，

it can make them rotate,

會使它們旋轉，

as their positive and negative regions are pushed and pulled in different directions.

因為它們的正電區和負電區 被往不同方向推拉。

The frequency the light is traveling at

光的傳播頻率

also determines how it interacts with matter.

也決定了它與物質的相互作用方式。

Microwaves interact strongly with the water molecules found in most foods.

微波與多數食物中的水分子之間 有著強烈的相互作用。

Essentially, they make the molecules jostle against each other,

基本上，它們使分子彼此摩擦，

creating frictional heat.

產生摩擦熱。

Household microwave ovens are fitted with cavity magnetrons.

家用微波爐配備有空腔磁控管。

When you activate a microwave oven,

當您啟動微波爐時，

a heated element within the magnetron ejects electrons,

磁控管內的加熱元件會噴射出電子，

and a strong magnet forces them to spiral outwards.

強磁鐵會迫使它們向外螺旋式運動。

As they pass over the magnetron’s metallic cavities,

當電子經過磁控管的金屬腔時，

the electrons induce an oscillating charge,

電子產生振盪電荷，

generating a continuous stream of electromagnetic microwaves.

生成連續的電磁微波流。

A metal pipe directs the microwaves into the main food compartment,

一根金屬管將微波引導到 置放食品的主要隔間，

where they bounce off the metal walls

在此，微波從金屬壁上反彈

and penetrate a few centimeters into the food inside.

並穿透進食物幾厘米。

When the microwaves encounter polar molecules in the food, like water,

當微波遇到食物中的 極性分子（例如水）時，

they make them vibrate at high frequencies.

會使它們高頻率振動。

This can have interesting effects depending on the food's composition.

依食物成分不同， 這會產生特別的效果。

Oil and sugar absorb fewer microwaves than water,

油和糖吸收的微波比水少，

so if you microwave them alone, not much happens.

所以用微波爐單獨加熱油、糖， 不會有太大變化。

But when microwaves encounter a marshmallow,

但是，當微波遇到棉花糖，

they heat the moisture trapped within its gelatin-sugar matrix,

微波會加熱明膠糖基質中的水分，

making the hot air expand and the marshmallow puff.

使熱空氣膨脹，棉花糖膨化。

Butter is essentially a suspension of water droplets in fat.

基本上，奶油裏有水滴懸浮在脂肪中。

When microwaved, the water rapidly vaporizes,

加熱時，水迅速蒸發，

making the butter melt quickly— and sometimes, a bit violently.

使奶油快速融化，有時變化有點劇烈。

So microwaves heat food molecules mechanically, through friction—

因此，微波是透過摩擦 以機械方式加熱食物分子，

but they don't alter them chemically.

不會改變它們的化學組成。

Soup heated in the microwave is molecularly indistinguishable

用微波爐加熱的湯與 用爐子或烤箱加熱的湯

from soup heated using a stove or oven.

在分子上沒有區別。

The term “microwave radiation” can be alarming.

「微波輻射」一詞可能令人擔憂。

But in physics, radiation simply describes any transfer of energy across a gap.

但在物理學中，輻射只是描述 任何跨越間隙的能量轉移。

High frequency, ionizing radiation may be harmful

高頻電離輻射可能有害，

because it can strip electrons from molecules, including DNA.

因為它會剝奪分子 （包括 DNA）中的電子。

However, microwaves aren’t energetic enough to alter chemical bonds.

然而，微波的能量不足以改變化學鍵。

And microwave ovens are designed to prevent leakage—

而且，微波爐的設計旨在防止洩漏，

for safety and efficiency’s sake.

以確保安全和效率。

Nonetheless, to totally limit exposure,

儘管如此，為了完全防止暴露，

experts recommend simply standing a few feet away when a microwave oven is on.

專家建議在微波爐運行時 保持幾英尺的距離。

Microwaving metal is dangerous, though, right?

不過，用微波爐加熱金屬 很危險，對嗎？

Well, it depends.

嗯，這要看情況。

Metals are conductors,

金屬是導體，

meaning their electrons are loosely bound to their atoms

這意味著它們的電子 與其原子鬆散地結合，

and move freely in response to electric fields.

並隨電場自由移動。

Instead of absorbing microwave radiation,

金屬的電子不會吸收微波輻射，

the metal’s electrons concentrate on the surface,

而是集中在表面，

leading to high voltages at sharp edges, corners, and small gaps.

導致尖銳邊緣、角落 和小間隙會產生高電壓，

This includes areas between the creases on a sheet of aluminum foil,

這包括鋁箔、叉子的尖端

the prongs of a fork,

或金屬物體上的摺痕

or a metal object and the microwave oven’s metal walls.

與微波爐的金屬壁之間的區域。

Sometimes, voltages get high enough to strip electrons

有時，電壓高到

from the surrounding air molecules.

足以從周圍的空氣分子中剝離電子。

This electrically charged gas, or plasma, may then form lightning-like sparks

這種帶電氣體，或稱電漿， 可能會形成閃電般的火花，

and grow as it absorbs more microwaves.

並隨著吸收更多的微波而增長。

Once the oven is turned off, the plasma dissipates.

一旦關閉烤箱，電漿就會消散。

But not all metal objects spark in the microwave—

但並非所有金屬物體 都會在微波爐中產生火花，

though they might make things cook a little unevenly.

儘管它們可能會使食物煮得不均勻。

In fact, a lot of microwavable packaging takes advantage of this,

事實上，許多微波包裝 利用了這一點，

using a thin metal coating to crisp the food’s surface.

使用薄金屬塗層使食物表面變脆。

And overall, as long as it doesn't approach the oven's walls,

整體來說，只要不接觸微波爐壁，

leaving a metal spoon in a microwaving bowl of soup

將金屬湯匙留在微波爐裡的湯碗中

should be a pretty uneventful affair.

應該還是滿安全的。

That’s just another neat benefit of cooking with RADAR.

這只是用雷達來烹飪的另一個好處。