Why a Grape Turns into a Fireball in the Microwave
wired.com
wired.com
In a microwave oven, resonance between two grapes can ionize the air, creating plasma. The wavelength of 2.45GHz microwaves = 12cm, but the grape's refractive index of ~10 slows down the wave 10x, decreasing the wavelength to about 1.2cm...about the size of a grape. This causes resonance at the center of each grape, just like you can hear "boomy" bass in certain parts of a room.
When two grapes touch, this creates a mode (or standing wave) between them, which builds up enough energy to ionize the air, allowing electrons to flow. If you look at the plasma spectrum, you can see spikes for the sodium (Na) and potassium (K) ions in the grapes.
SCIENCE, BIATCH!
I know what I'm doing tomorrow with our old microwave.
Generally the bulb would explode, we presumed due to the heat causing internal pressure. Though at one point a bulb got really hot and melted a sort of bubble on the side. It seemed to provide enough space for the heated air so it never exploded and we could use it again and again.
You can use different gases in the bottle for different plasmas.
I'm finding it hard to imagine a situation where I desperately need to make plasma but I'll file this one away just in case. ;)
Stars do it easily, because the confinement / pressure is provided by immense gravity which very conveniently works to compress a huge load of gas into a point space.
More importantly, would this be bad for... someone else's microwave at a party?
1) Lead pencil drawing on paper (ideally a circle) in the microwave.
2) Incandescent light bulb in the microwave.
3) CD in the microwave.
4) Grape!
For some reason I was not able to reproduce the effect with drinking glass, linked above, though.
If you don't want to use many grapes, put a water glass in it.
solution, for those busy or lazy: https://www.youtube.com/watch?v=y8mzDvpKzfY
When you accelerate, the gas in your car behaves like a fluid, piling up in the rear of the vehicle. Helium balloons climb up the density gradient of air, essentially seeking the lowest density point.
That area of low density is at the front of the car as you accelerate. So, the balloon moves forward as you accelerate.
What matters is that the direction of the buoyant force is precisely opposite the direction of the overall force acting on the fluid (because that's what keeps the hypothetical fluid that your balloon displaces from moving due to said overall force). Importantly, this overall force needs to be measured in the reference frame of the fluid, which in this case is accelerating.
OK, so let's draw out a force diagram on the air inside the car. There's a force upward from the floor, exactly balanced by the force of gravity down. There's similarly a force from the back of the car , which is what's accelerating the air, from the point of view of a non-accelerating observer. From the point of view of an observer in the car, however, the air is _not_ accelerating, but the force from the back of the car is still there. So there must be a force backwards on the air, to balance the force of the back of the car. You can call it "inertial force" or "gravity" (in the general-relativistic sense) but the upshot is the same: the overall force on the air is down and backwards, so the buoyant force is up and forward, along the same line. For a helium balloon the buoyant force is stronger than "gravity", so it goes up and forward.
Not my proudest moment.
I dunno, my turbo miata will light up the rear tires at 60mph if you drop a gear and stomp on the throttle
I later reckoned a cherry tomato would probably do the same thing and it definitely does. I remember at the time thinking the grape gave a whitish-blue arc where the tomato gave an orangey-red one but not sure whether I was imagining that.
Probably two of the safest microwave tricks to do, as it is just food after all, but the CD one is definitely worth the temporary smell of burnt plastic.
However, your eye/brain is seeing energy in a bunch of spectral bands, and making a decision as to what colour to call it.
https://en.wikipedia.org/wiki/Ball_lightning#Microwave_cavit...
This might have applications for really bad-ass cancer treatments. Build nano-particles that have this strange property, that will be consumed by cancer cells but not by healthy cells (note: this is the hard part). Then explode the cancer cells via microwaves!
I'm certain there are an incredible number of flaws in this plan.
Aww, man, the dude just said that is has to be “watery enough”. Pay attention to what you’re typing, Wired.
Their conclusions: The grape is less like an antenna and more like a trombone, though for microwaves instead of sound. When you play a trombone, you push vibrating air into it. The trombone will only sustain vibrations of a particular wavelength—the musical note you hear—depending on where you’ve positioned the slide. Only certain wavelengths, known as standing waves, fit perfectly inside the trombone. As vibrating air of various wavelengths enter the trombone, the standing waves add constructively, while other wavelengths cancel each other out. In other words, the trombone amplifies the standing waves and mutes all others.
The grape, incidentally, is the perfect size for amplifying the microwaves that your kitchen machine radiates. The appliance pushes microwaves into the two grape halves, where the waves bounce around and add constructively to focus the energy to a spot on the skin. Both grape halves happen to focus the energy to the same tiny point. That intense energy jostles the atoms and molecules at that spot, heating them up so much that they can no longer hold onto their electrons, which turns them into a plasma—and boom, fireball.
tl;dr: constructive EM wave interference from the grape seed.
https://books.google.com/books?id=8_lfAgAAQBAJ&printsec=fron...
"Ceramic antenna" is a term that will yield information on the applications of this idea to antennas.