शैडोइंग अभ्यास: Why can't you put metal in a microwave? - Aaron Slepkov - YouTube के साथ अंग्रेजी बोलना सीखें

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American engineer Percy Spencer developed World War II RADAR technology that helped detect Nazi airplanes— but it would soon have other surprising applications.

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American engineer Percy Spencer developed World War II RADAR technology that helped detect Nazi airplanes— but it would soon have other surprising applications.

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One day in 1945, Spencer was standing near a RADAR instrument called a magnetron, a device that produced high-intensity microwaves that could reflect off planes.

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

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He exposed other things to the magnetron and, sure enough, popcorn kernels popped, and an egg—well— exploded onto a colleague.

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Soon after, the first microwave oven became available, operating using the very same technology.

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So, how does it work?

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

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These oscillations span a range of frequencies comprising the electromagnetic spectrum.

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The higher the frequency, the more energetic.

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Gamma rays and X-rays have the highest frequencies; microwaves and radio waves, the lowest.

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Generally, light’s oscillating electric field exerts forces on charged particles, like the electrons in a molecule.

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When light encounters polar molecules, like water, it can make them rotate, as their positive and negative regions are pushed and pulled in different directions.

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The frequency the light is traveling at also determines how it interacts with matter.

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

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Essentially, they make the molecules jostle against each other, creating frictional heat.

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Household microwave ovens are fitted with cavity magnetrons.

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When you activate a microwave oven, a heated element within the magnetron ejects electrons, and a strong magnet forces them to spiral outwards.

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As they pass over the magnetron’s metallic cavities, the electrons induce an oscillating charge, generating a continuous stream of electromagnetic microwaves.

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A metal pipe directs the microwaves into the main food compartment, where they bounce off the metal walls and penetrate a few centimeters into the food inside.

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When the microwaves encounter polar molecules in the food, like water, they make them vibrate at high frequencies.

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

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Oil and sugar absorb fewer microwaves than water, so if you microwave them alone, not much happens.

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But when microwaves encounter a marshmallow, they heat the moisture trapped within its gelatin-sugar matrix, making the hot air expand and the marshmallow puff.

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Butter is essentially a suspension of water droplets in fat.

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When microwaved, the water rapidly vaporizes, making the butter melt quickly— and sometimes, a bit violently.

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So microwaves heat food molecules mechanically, through friction— but they don't alter them chemically.

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Soup heated in the microwave is molecularly indistinguishable from soup heated using a stove or oven.

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The term “microwave radiation” can be alarming.

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

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High frequency, ionizing radiation may be harmful because it can strip electrons from molecules, including DNA.

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

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And microwave ovens are designed to prevent leakage— for safety and efficiency’s sake.

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Nonetheless, to totally limit exposure, experts recommend simply standing a few feet away when a microwave oven is on.

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Microwaving metal is dangerous, though, right?

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Well, it depends.

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Metals are conductors, meaning their electrons are loosely bound to their atoms and move freely in response to electric fields.

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Instead of absorbing microwave radiation, the metal’s electrons concentrate on the surface, leading to high voltages at sharp edges, corners, and small gaps.

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This includes areas between the creases on a sheet of aluminum foil, the prongs of a fork, or a metal object and the microwave oven’s metal walls.

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Sometimes, voltages get high enough to strip electrons from the surrounding air molecules.

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This electrically charged gas, or plasma, may then form lightning-like sparks and grow as it absorbs more microwaves.

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Once the oven is turned off, the plasma dissipates.

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But not all metal objects spark in the microwave— though they might make things cook a little unevenly.

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In fact, a lot of microwavable packaging takes advantage of this, using a thin metal coating to crisp the food’s surface.

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And overall, as long as it doesn't approach the oven's walls, leaving a metal spoon in a microwaving bowl of soup should be a pretty uneventful affair.

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

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शैडोइंग अभ्यास: Why can't you put metal in a microwave? - Aaron Slepkov - YouTube के साथ अंग्रेजी बोलना सीखें

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