# Why are microwaves reflected by the door?

• Emissive
In summary: What Sophie is trying to get you to understand is that you cannot say "a photon approaches the screen" or "what is the size of a photon". A photon is simply not a little particle that would behave in this manner.
Emissive
Hi,

I am wondering why microwaves don't escape through the door?

The most common answer seems to be that the wavelength of microwave ovens is about 10-15cm which is much larger than the 1-2mm holes in the grille. But isn't the wavelength of light really just within a vector space of mathematics describing its motion not a description of the actual particle which remains point like? (Well - point like if you could find it in the probability density). We are not really looking at waves in reality as the have no amplitude - making a light wave from front view always look like a dot - and dots would fit through the holes in microwave...wouldn't they?

Photons are not a universal substitute for classical electromagnetism. Both descriptions are valid and suitable, each in its own restricted domain. Photons are meaningful when the fields are weak and the energies high. This is not the case in a microwave oven, where we still use electric and magnetic fields obeying Maxwell's Equations.

The fields are confined to the interior of a microwave oven by a metallic mesh (size about 1 mm) that covers the walls and door and reflects the microwaves.

Yes...I guess electromagnetism does explain it but I hoping for the QED interpretation?

Can we imagine a single microwave photon fired at a 1mm hole in the mesh - why would it bounce back?

Do you already understand QED? If not, why do you want an explanation based on something you don't understand?

The part I am obviously not understanding is the dimensionallity of the photon. Is there a relationship between wavelength and the chance it will make it through a small opening?

No, this is the part you are not understanding:
Photons are not a universal substitute for classical electromagnetism. Both descriptions are valid and suitable, each in its own restricted domain. Photons are meaningful when the fields are weak and the energies high. This is NOT THE CASE in a microwave oven, where we still use electric and magnetic fields obeying Maxwell's Equations.

The material that the screen is made of makes a crucial difference here. A cardboard screen with the same size holes wouldn't block the microwaves at all, or only minimally.

It's really unfair of photons not to behave like little bullets, isn't it? Life would be so much simpler if they were - and we wouldn't have to worry about diffraction and all the rest of modern Physics.
This OP is so much the product of really naff Science teaching and the poor level of presentation of Science on the Media. Why don't people appreciate that Science is Really Hard and not very approachable at all?

Yes - the emisivity of screen within the wavelength concerned certainly has major impact. The is why we wrap our buildings in foil to reflect some of the infrared radiation and apply low-e coatings to glass to assist with heat loss/gain. Cardboard = no chance (virtually) metal = high chance of reflecting...microwaves in this case.

Ok - I think I worked this out by drawing it. Please correct me if I wrong...

A series of photons approach the screen. Their wavelength is 10x the size of the screen openings and the screen is 30% open. 30% of The photons do pass through the openings (the others hit the screen solid and reflect back) but they pass through every opening and arrive at a point on the side with varying amplitudes which then deconstructively build giving a very limited probability that they will be found there.

When the wavelength is changed to smaller than the opening we get a higher probability amplitude directly in front of the opening and deconstructive ones at holes further away.

Emissive said:
A series of photons approach the screen.

You are already wrong. Photons do not work like this. Instead, it is an EM wave of a certain energy and frequency that is emitted and propagates towards the screen. When the wave interacts with something, and by that I mean when it actually transfers energy, it will do so in little discrete amounts that we label as photons.

What sophie is trying to get you to understand, and what he has pounded into my head previously, is that you cannot say "a photon approaches the screen" or "what is the size of a photon". A photon is simply not a little particle that would behave in this manner.

Drakkith said:
You are already wrong. Photons do not work like this. Instead, it is an EM wave of a certain energy and frequency that is emitted and propagates towards the screen. When the wave interacts with something, and by that I mean when it actually transfers energy, it will do so in little discrete amounts that we label as photons.

What sophie is trying to get you to understand, and what he has pounded into my head previously, is that you cannot say "a photon approaches the screen" or "what is the size of a photon". A photon is simply not a little particle that would behave in this manner.

"But other fell into good ground, and brought forth fruit, some an hundredfold, some sixtyfold, some thirtyfold."

You have no idea how good that makes me feel!

sophiecentaur said:
"But other fell into good ground, and brought forth fruit, some an hundredfold, some sixtyfold, some thirtyfold."

You have no idea how good that makes me feel!

As hard as it was to wrap my head around initially, everything involving light makes a LOT more sense now.

Drakkith said:
As hard as it was to wrap my head around initially, everything involving light makes a LOT more sense now.
One has to chuck out an immense amount of baggage to get there. Most of it came from 'Education', too.

sophiecentaur said:
One has to chuck out an immense amount of baggage to get there. Most of it came from 'Education', too.

Chuck it, burn it, and bury it!

Interesting.

I would have thought we could say a photon approaches the screen? It is one packet of em energy.

Don't we only ever "see" em waves as photons or discrete packets of energy...We don't get two halfs of a photon showing up. It is only when they transfer energy that they become visible everything in-between is a mathematical model. we could emit one photon at a time with a break - that's a series of photons isn't it?

Emissive said:
Don't we only ever "see" em waves as photons or discrete packets of energy...We don't get two halfs of a photon showing up. It is only when they transfer energy that they become visible everything in-between is a mathematical model. we could emit one photon at a time with a break - that's a series of photons isn't it?

It is in the sense that you measure the energy of the EM wave one packet at a time, with a large time between each packet being delivered to your sensor. However you cannot claim that during transit the photon itself was moving like a little bullet or anything. That simply cannot explain things like interference that are properties of waves.

If a photon is detected by a sensor in a certain place in front of the screen then all you can say is that it was detected there. You can say nothing about how (what route) it got there or how big it is/was - except by describing the wave behaviour of the energy and, if you want to, saying that relates to the statistical probability of detecting the photon. The photon is only there when it's being detected. You have no idea how it got there as a photon and if you go looking for a photon somewhere else and detect one, it may affect the probablilty of finding one in the original spot.
This is like trying to decide which slit a photon chose to go through one of the 'two slits' in that well known experiment. If you have a detector to 'catch all the photons' that go through one slit, you get no interference pattern because you have eliminated the possibility of a photon going through that slit.

Agreed.

But the interference patterns which manifest in locality is maths - a vector space designed to construct and assertian the photons properties but its not actual space in the real world - so I don't see a problem in visualising a photon as point as that is how is shows up (albeit impossible to ever actually locate)...it certainly doesn't move like a bullet as in classical mechanics (because its a wave in it vector space and a bullet is a line in its vector space).

Emissive said:
Agreed.

But the interference patterns which manifest in locality is maths - a vector space designed to construct and assertian the photons properties but its not actual space in the real world - so I don't see a problem in visualising a photon as point as that is how is shows up (albeit impossible to ever actually locate)...it certainly doesn't move like a bullet as in classical mechanics (because its a wave in it vector space and a bullet is a line in its vector space).

The math describes a real world effect though. And if it is impossible to locate, can you even say it's "real"?

## 1. Why do microwaves get reflected by the door of a microwave oven?

Microwaves are electromagnetic waves with a wavelength of about 12 centimeters. These waves are easily absorbed by food and water molecules, causing them to vibrate and generate heat. The door of a microwave oven is designed to be reflective to these microwaves, preventing them from escaping and keeping the heat inside the oven.

## 2. What material is used to make the door of a microwave oven?

The door of a microwave oven is typically made of a conductive metal, such as steel, with a layer of conductive mesh or perforated metal on the inside. This allows the microwaves to be reflected and contained within the oven.

## 3. Can microwaves pass through the door of a microwave oven?

No, microwaves cannot pass through the door of a microwave oven. The door is specifically designed to be reflective to these waves in order to keep them inside the oven and avoid any potential harm to the user.

## 4. Is it dangerous to stand in front of a microwave oven while it is in use?

No, it is not dangerous to stand in front of a microwave oven while it is in use. The door of the oven is designed to reflect the microwaves back into the oven, and the FDA has strict regulations on the amount of radiation that can leak from a microwave oven.

## 5. Why can I see through the door of a microwave oven?

The door of a microwave oven may appear to be transparent, but in reality, it is made of a material that allows only visible light to pass through. Microwaves, which have a much longer wavelength, cannot pass through this material and are reflected instead.

Replies
7
Views
1K
Replies
4
Views
3K
Replies
3
Views
1K
Replies
7
Views
4K
Replies
5
Views
3K
Replies
2
Views
2K
Replies
13
Views
3K
Replies
29
Views
2K
Replies
2
Views
3K
Replies
1
Views
928