Why can't waves escape the micro oven?

[hobz]

I was wondering why the microwaves generated in a micro oven, cannot escape the metal grid that is located just behind the glass in the door of the micro oven?

[insane_alien]

the wavelength of a microwave is vastly bigger than the holes in the grid. if you could see in the microwave spectrum the grid would appear like a flat sheet of metal.

[thedarkshade]

the wavelength of a microwave is vastly bigger than the holes in the grid.

Yeah, a wavelength 'in there' is typically ~12.3cm. That's big enough!

[hobz]

But isn't the wavelength "along" the ray of the wave? I mean, since EM waves are transversal waves, shouldn't it be their amplitude that "got stuck" in the holes?

[swansont]

But isn't the wavelength "along" the ray of the wave? I mean, since EM waves are transversal waves, shouldn't it be their amplitude that "got stuck" in the holes?

 

The amplitude is the strength of the E or B field, not a spatial extent. A classical picture is going to be of limited value for this quantum description, but the spatial extent of the field and the strength of the field aren't the same. Picture a field of a certain strength, but with the characteristic size given by the wavelength.

[hobz]

the wavelength of a microwave is vastly bigger than the holes in the grid. if you could see in the microwave spectrum the grid would appear like a flat sheet of metal.

Is this because of the angular resolution and Rayleigh criterion?

 

The amplitude is the strength of the E or B field, not a spatial extent. A classical picture is going to be of limited value for this quantum description, but the spatial extent of the field and the strength of the field aren't the same. Picture a field of a certain strength, but with the characteristic size given by the wavelength.

I am not sure if I understand what you mean by "size"?

[swansont]

I am not sure if I understand what you mean by "size"?

 

You run into trouble trying to explain quantum effects with a classical description, since there are going to be instances where the classical description fails, so forgive me if this sounds vague. The distance over which you have an electric field (that you might associate with the size of the photon) is not the same as the amplitude of the field strength. i.e. the graph that usually depicts the electromagnetic wave has axes of E and z, not x and z.

[hobz]

I see. Does a graphical interpretation of the wave even exist? And could it explain (graphically) why the wave is not able to penetrate the grid?

[Mr Skeptic]

I see. Does a graphical interpretation of the wave even exist? And could it explain (graphically) why the wave is not able to penetrate the grid?

 

You could think of the wave having a size (its wavelength). If you consider a photon to be a bouncy ball moving at c the size of its wavelength, it is easy to imagine it bouncing off a screen with small holes.

 

However, that is not a particularly good description of light, as it is actually an electromagnetic wave rather than a ball. The fields have a size that they have significant strength in, and if they are large enough fields, they can induce motions of electrons in a conductor. The moving electrons generate opposing fields, and this is (a somewhat more accurate description) of why large EM waves bounce off metal. Smaller waves are the "size" of large molecules, and even smaller ones are the "size" of atoms; these will be unable to reflect from metal like the larger waves.

[hobz]

Mr Skeptic:

 

So the wave is reflected due to an opposing wave induced in the metal?

And this opposing wave can only be induced, if the metal is spread out enough (meaning that holes in the metal must not reduced the metal below a certain size), to allow a full wavelength of the incoming wave to induce a full wavelength of the outgoing (opposing) wave? If a hole disrupts a full wavelength, then the wave cannot be "created" in the metal, and thus not oppose anything?

 

Can anyone point me to a direction, in which I can read more about this description of opposing fields?

[swansont]

It's not opposing fields, per se, that causes reflection. It's the inability (or difficulty, if you'll excuse the anthropomorphic nature of that) for the wave to exist in the material, so there's a boundary condition in effect. You get reflection because you have to in order to conserve energy.

[hobz]

Nice. Didn't know that.

So how can the wave exist in the material, if the holes are bigger?

[hobz]

Can you guys recommend a book, a chapter from a book, a website or video, that explains this in greater detail?

[kevinalm]

The outgoing wave induces currents in the conductive plate. These currents are phased such that in the absence of the outgoing wave a bidirectional plane wave would be emitted 180 degrees out of phase, both into and out of the microwave. Sum that with the original outgoing wave and you have zero transmitted and 100 percent reflected.

 

Punching holes in the plate disturbs the current flow and interferes with both the cancelation of the transmitted wave and creation of the reflected wave. This isn't too bad until the hole size approaches wavelength, then the behavior switches quickly to transmission. I'm not entirely clear on why, but iirc it relates to diffraction and Raliegh effect, and to interference for an array of holes.

 

Given that the quanta for a microwave photon would be on the order of 10^-5 ev, I can't imagine that any discernable quantum mechanisms are involved. I suppose if you cooled the interior of the oven with liquid He and... Of course you could always create a coresponding quantum description, but classical E/M is quite able to handle it, with a little wave optics thrown in.

[Ti]

Hey is this why you noticed you keep heating the food and it wont get hot? Somebody must have screw it up, right?

[DavyJonesLoquet]

They do, and that is why they should eb banned since they are devolutions of super-fractioned light and have dis-temporal effects on gluonic functions. Basically, they interrupt the glue in your matter and should be banned. Only lead stops microwaves and any microwave radiation will eventually destroy your RNA sequence and give you cancer.

[iNow]

They do, and that is why they should eb banned since they are devolutions of super-fractioned light and have dis-temporal effects on gluonic functions. Basically, they interrupt the glue in your matter and should be banned.

 

I'll tell you what. I'll take you seriously when you provide a few reputable sources supporting this claim. Until then, all readers should consider it unproven garbage from an unknown person.

 

 

Ooohh... time for another Hot Pocket and some popcorn.

[swansont]

They do, and that is why they should eb banned since they are devolutions of super-fractioned light and have dis-temporal effects on gluonic functions. Basically, they interrupt the glue in your matter and should be banned. Only lead stops microwaves and any microwave radiation will eventually destroy your RNA sequence and give you cancer.

 

Been breathing popcorn fumes a little too much?

[Klaynos]

Those evil photons somehow effecting the strong force! DAMN THEM!!!!

[mooeypoo]

They do, and that is why they should eb banned since they are devolutions of super-fractioned light and have dis-temporal effects on gluonic functions. Basically, they interrupt the glue in your matter and should be banned. Only lead stops microwaves and any microwave radiation will eventually destroy your RNA sequence and give you cancer.

Is that even English?

 

DavyJonesLoquet, let me give you a piece of advice: We don't quite accept know-it-alls-with-no-proof-and-bad-science theories, not in this forum, or the biology forum, or the speculations forum for that matter.

 

Cite your words, and do speak English.

 

And.. read the rules.

 

 

~moo

[hobz]

It's not opposing fields, per se, that causes reflection. It's the inability (or difficulty, if you'll excuse the anthropomorphic nature of that) for the wave to exist in the material, so there's a boundary condition in effect. You get reflection because you have to in order to conserve energy.

 

I have re-thought this answer and am wondering why higher frequencies CAN exists in the material. I assume that they can, because they will travel through the grid of the oven. Why is that?

[swansont]

I have re-thought this answer and am wondering why higher frequencies CAN exists in the material. I assume that they can, because they will travel through the grid of the oven. Why is that?

 

There are holes in it — if the wavelength is short enough that the radiation can pass through the holes without interacting with the metal, they will. These holes can be the spaces between atoms for really high frequencies.

[hobz]

Thanks for picking up on this thread again.

 

Does that imply that at higher frequencies (than that of an ordinary oven) only some of the waves escape, while other are reflected since there aren't holes all over, and where there are no holes the required wavelength to escape is smaller than that of an incoming wave?

 

Earlier on there was an explanation involving opposing fields that canceled out outside the oven, while creating standing waves on the inside. Is the true or false?

 

The real problem is picturing why it is obvious or at least reasonable to understand how a wavelength is related to something spacial as a hole in a metal.

The property of wavelength must have a specific interpretation in space, right?

[swansont]

Thanks for picking up on this thread again.

 

Does that imply that at higher frequencies (than that of an ordinary oven) only some of the waves escape, while other are reflected since there aren't holes all over, and where there are no holes the required wavelength to escape is smaller than that of an incoming wave?

 

Earlier on there was an explanation involving opposing fields that canceled out outside the oven, while creating standing waves on the inside. Is the true or false?

 

The real problem is picturing why it is obvious or at least reasonable to understand how a wavelength is related to something spacial as a hole in a metal.

The property of wavelength must have a specific interpretation in space, right?

 

 

What I'd expect is that at some wavelength you'll start seeing leakage, but the waves will diffract. As the wavelength gets shorter, there will be less diffraction, and the transmission will look more like the hole pattern.

 

The cancellation view could possibly work, since waves follow superposition — you can't really say that an area is dark because two waves canceled or because there was no wave there in the first place. You have a standing wave because other wavelengths cancel is a valid way to look at things.