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

翻译人员: Jing Quan 校对人员: Yanyan Hong

American engineer Percy Spencer developed World War II RADAR technology

美国工程师珀西·斯宾塞（Percy Spencer） 开发了二战雷达技术，

that helped detect Nazi airplanes—

该技术有助于探测纳粹飞机——

but it would soon have other surprising applications.

但很快它有了其他令人惊喜的应用。

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

1945 年的某一天，斯宾塞站在一台名为

called a magnetron,

磁控管的雷达仪器旁边，

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

该设备可产生能在飞机上反射的高强度微波。

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

突然，他注意到口袋里的糖果棒融化了。

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

他将其他东西暴露在磁控管中，果然，

popcorn kernels popped,

爆米花弹出来了，

and an egg—well— exploded onto a colleague.

一个鸡蛋飞溅到了同事身上。

Soon after, the first microwave oven became available,

不久之后，第一台微波炉问世，

operating using the very same technology.

其运行技术（和磁控管）完全相同。

So, how does it work?

那么，它是如何运作的？

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

所有光能都以振荡的电场和磁场波动性传播。

These oscillations span a range of frequencies

这些振荡跨越了一系列频率，

comprising the electromagnetic spectrum.

包括电磁频谱。

The higher the frequency, the more energetic.

频率越高，能量越大。

Gamma rays and X-rays have the highest frequencies;

伽玛射线和 X 射线的频率最高；

microwaves and radio waves, the lowest.

微波和无线电波的频率最低。

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

通常，光的振荡电场对带电粒子施加压力，

like the electrons in a molecule.

例如分子中的电子。

When light encounters polar molecules, like water,

当光遇到极性分子（例如水）时，

it can make them rotate,

它会使水分子旋转，

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

这是因为极性分子的正负区域 被推向了不同的方向。

The frequency the light is traveling at

光的传播频率

also determines how it interacts with matter.

也决定了它与物质相互作用的方式。

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

微波与大多数食物中的水分子强烈相互作用。

Essentially, they make the molecules jostle against each other,

本质上，它们使分子相互碰撞，

creating frictional heat.

产生摩擦热。

Household microwave ovens are fitted with cavity magnetrons.

家用微波炉装有腔体磁控管，

When you activate a microwave oven,

当你开启微波炉时，

a heated element within the magnetron ejects electrons,

磁控管内的加热元件会喷出电子，

and a strong magnet forces them to spiral outwards.

强磁体迫使它们向外螺旋。

As they pass over the magnetron’s metallic cavities,

当它们穿过磁控管的金属腔时，

the electrons induce an oscillating charge,

电子会产生振荡电荷，

generating a continuous stream of electromagnetic microwaves.

产生连续的电磁微波流。

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

金属管将微波引导到主要的食物空间，

where they bounce off the metal walls

在那里它们从金属墙上反弹，

and penetrate a few centimeters into the food inside.

并可穿透食物内部几厘米深。

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

当微波遇到食物中的极性分子（例如水）时，

they make them vibrate at high frequencies.

它们会使水分子以高频振动。

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

根据食物的成分，这可能会产生有趣的效果。

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.

因此，如果单独用微波炉加热， 不会有什么额外变化。

But when microwaves encounter a marshmallow,

但是，当微波炉遇到棉花糖时，

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

它们会加热残留在其明胶糖基质中的水分，

making the hot air expand and the marshmallow puff.

从而使热空气膨胀，棉花糖膨化。

Butter is essentially a suspension of water droplets in fat.

黄油本质上是水滴在脂肪中的悬浊液，

When microwaved, the water rapidly vaporizes,

用微波炉加热时，水迅速蒸发，

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

使黄油快速融化，有时甚至有点剧烈了。

So microwaves heat food molecules mechanically, through friction—

因此，微波通过摩擦机械地加热食物分子，

but they don't alter them chemically.

但它们不会对食物分子进行化学改变。

Soup heated in the microwave is molecularly indistinguishable

汤是用微波炉还是炉子或烤箱加热的，

from soup heated using a stove or oven.

在分子上没有区别。

The term “microwave radiation” can be alarming.

“微波辐射” 一词可能令人警觉。

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

但在物理学中， 辐射只是描述任何能量跨越间隙的传递。

High frequency, ionizing radiation may be harmful

高频电离辐射可能是有害的，

because it can strip electrons from molecules, including DNA.

因为它可以从分子中剥离电子，包括 DNA。

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

但是，微波的能量不足以改变化学键。

And microwave ovens are designed to prevent leakage—

微波炉在设计上就是防泄漏的，

for safety and efficiency’s sake.

既是为了安全也是效率。

Nonetheless, to totally limit exposure,

尽管如此，为了完全杜绝暴露在辐射下，

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

专家建议在微波炉使用时 直接站在几英尺远的地方。

Microwaving metal is dangerous, though, right?

但是，用微波炉加热金属很危险，对吧？

Well, it depends.

好吧，这要看情况。

Metals are conductors,

金属是导体，

meaning their electrons are loosely bound to their atoms

这意味着它们的电子与原子结合松散，

and move freely in response to electric fields.

并在电场的作用下自由移动。

Instead of absorbing microwave radiation,

金属的电子不会吸收微波辐射，

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.

从而在锋利的边缘、角落和小间隙处产生高电压。

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

这包括铝箔纸上的折痕、

the prongs of a fork,

叉子

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

或金属物体尖端以及微波炉的金属壁。

Sometimes, voltages get high enough to strip electrons

有时，电压会高得足够

from the surrounding air molecules.

从周围的空气分子中剥离电子。

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

然后，这种带电的气体或等离子体 可能会形成电火花，

and grow as it absorbs more microwaves.

并随着吸收更多的微波而变多。

Once the oven is turned off, the plasma dissipates.

烤箱关闭后，等离子体就会消散。

But not all metal objects spark in the microwave—

但是，并非所有的金属物体 都会在微波炉中产生火花，

though they might make things cook a little unevenly.

尽管它们可能会使食物煮得有点不均匀。

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

实际上，许多可微波炉加热的包装 都利用了这一点，

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

使用薄薄的金属涂层使食物表面变脆。

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

总的来说，只要它不靠近烤箱的墙壁，

leaving a metal spoon in a microwaving bowl of soup

在装有微波炉的汤碗里放一把金属勺子

should be a pretty uneventful affair.

应该没什么关系。

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

这只是使用“雷达”烹饪的另一个好处。