/sci/ - Science & Math

don't microwaves heat from the inside out?

>>6262545
Yeah, that's what I thought too. OP you sure? I thought the longer wavelengths penetrate better

>>6262545
Then why is it that whenever I microwave something the inside is all cold?

That doesn't make sense.

>>6262585
You have a shitty microwawe thats why, it heats your food unevenly

>>6262593
The outside is hot. The inside is cold. Also, I'm pretty sure microwaves work by blasting your food with microwave radiation, which heats up the first thing it touches - the outside of the food.

>>6262550
>>6262545
>>6262593

this reminds me when microwaves first came out, i worked at a retail store and we got to use them for free, people at my work were trying to use them as ovens to cook turkeys and shit lol

>>6262585
this is true sometimes. I thawed some frozen tomato soup the microwave the other day. The outer part was boiling while there was still a big block of soup-ice in the middle.

>>6262781
No, it's true all the time. That's how microwaves work.

http://en.wikipedia.org/wiki/Microwave_oven
>A common misconception is that microwave ovens cook food "from the inside out", meaning from the center of the entire mass of food outwards.

So in theory, a conical beam of something that penetrates deeper, like X-rays, would heat the center first, while not being concentrated enough to burn the outside of your food the way a regular microwave does.

>>6262613
Dude, you must be like, 80.

>>6262613
oldfag dettected

>>6262500
>heat food ...using a conical X-ray beam

no. X-ray beams require significant energy sources to generate (and large machinery, most of it is hidden behind the wall at your dentist's office). But perhaps more importantly, x-rays will ionize the material. This is bad for you.

>>6262850
also left out, food is for the most part completely transparent to x-rays, focused or not. it would be a collosal waste of energy to actually get it hot.

>>6262855
Sure - but would it work? It might be completely impractical, but could we heat food evenly from the inside out with the same speed as a regular microwave?

>>6262861
>with the same speed
nope. its not going to happen, OP. give up your dreams.

>>6262863
nooooooooo.....

Food isn't mostly transparent to microwaves (unlike the plastic in your picture being mostly transparent to the laser frequency) so you could only do this to a relatively shallow depth.

Also, if you did this you'd have a tiny dot of carbonized food in the middle with the rest of the food being cold. The point of reheating food is to get the whole thing pretty hot.

>>6263066
>a tiny dot of carbonized food in the middle
But it rotates, no?

>microwave brownies
>entire pan is edges

>>6262790
So what is the relation between wavelength and penetrating power? Long wavelengths like radio can easily go through concrete. ELF communication can penetrate thousands of feet of water. Shorter visible light can't penetrate a piece of tinfoil. But even shorter wavelengths like x-ray can.

Any physics people around to educate us math people?

>>6262500
>conically focused
Seriously?

Not sure how these things are made, but if it's anything as you've described, it has to do with non-linear absorption of radiation. That means you have a pulsed laser (i.e. very intense for a short period) and you tightly focus it. This leads to very high electromagnetic field in the focus, which leads to multi-photon and avalanche ionization. Using a wavelength to which the substrate is transparent, e.g. IR in glass, you can get absorption only at the focal point. Voila.

X-rays will not heat the food. Microwaves will. They are on the other side of the ER spectrum from the visible light. For this to work, you will have to first design a microwave that can deliver short and powerful pulses, probably no longer than a nanosecond, picosecond more likely. Then you will have to focus it. The caveat here is that microwaves have a long wavethength (10cm or so), which means you can't focus it much smaller than that. So to get a proper power boost from focusing, which is usually 10^6 (mm-->um with IR) you will need to start with a microwave beam 100m across.

Having said that, your microwave would be the size of a house and cost $10M. You best stick to just mixing your food or letting the heat even out after you nuke it.

Trust me, I did a PhD in this shit.

>>6262545
No. If the material is microwavable, it absorbs microwaves just like any opaque material absorbs radiation: Beer's Law. Surface gets the most, and the deeper you go, the less is left.

>>6263118
Ah, yes, forgot to mention an important part. Your new microwave will need to use longer wavelength of radiation, the one to which the food is transparent to. That way you won't dissipate all of your energy at the surface, and it will actually make it to the focus. Sadly, longer wavelength means that you will have an even larger focus.

If your focus is too large, and it very well might be, then you're back to square one -- having your food heat up from the outside.

>>6263118
Thanks for the info. Although I have a question - the pulsed laser only gets absorbed at the focal point, but passes through the rest of the glass, correct?

So if X-rays pass through food the way light passes through glass, why don't they get absorbed at the focus?

Don't put the food in the center of the microwave turntable, idiots. That's the dead zone.

>>6263129
That's correct. At least that was the case with the lasers and glass I used (IR and silica based glass).

The absorption mechanism (2-step) is in the picture. The structure drawn is the valence band in the bottom, the conduction band in the top, and band gap in the middle. Band gap is pretty much what all the semiconductors are about.

(BTW, I just now realized that the mechanism for microwave absorption will be a bit different, if at all the same. That's because the transition is not between electron bands, but rather in molecular vibration states. So not sure if such multiphoton effect is at all possible with microwave)

X-ray is energetic enough to be absorbed without the need to focus. In fact, in this diagram it will shoot the electrons out of the valence band and all the way the fuck out. And its absorption occurs a bit differently. You will not be able to get the same non-linear effect that will allow you to heat just at the focus.

X-rays, depending on frequency, do pass through substances, because their absorption mechanism is different from visible radiation, but they still get absorbed and do damage. That's why getting any amount of X-ray exposure is not a good thing.

>>6263145
Stop using clear backgrounds on your pngs, it makes my hover expand thingy look like shit.

Thanks,
entitled 4chan asshats everywhere

>>6263161
>hover expand

ew, I just use click to expand inline, makes it easier to not accidentally expand stuff I don't want/need to

>>6263145
So basically, it's impossible to make a microwave that heats food from the inside out because any sort of radiation that would penetrate deep enough either a. wouldn't focus right or b. get absorbed right away?

Damn it. I guess we will always have to deal with microwaved burritos that are scorching on the outside but turn up cold in the center.

Onwards to 4th dimensional ovens.

Perhaps focused ultrasound?

>>6262808
>>6262815
or he lives in a poor country that didn't get microwaves until later
I really doubt he's old enough to have been around in the 50s-60s and still be posting on /sci/ and say something like "cook turkeys and shit lol"
or he's a liar

why not just 3D print hot food instead of microwaving food?

>>6263318
Microwaves only became common in the 70s.

Microwaves can penetrate just fine. The oven acts as a resonance cavity for the EM waves, creating a standing wave inside with different modes of resonance (http://en.wikipedia.org/wiki/Transverse_mode)) due to the short wavelength. These modes haves regions where the E field is at its maximum and minimum value, and since this is a standing wave, this is why your food gets heated unevenly. This is also why they add a rotating plate nowadays in them, which solves the problem.