[burag45 (OP)]

Bought a "Samsung MS23K3513AW" microwave. The doors close fine, but there's a noticeable gap on the left side of the door. I put a piece of bread on the outside of the crack and in 10 minutes the bread became slightly more crispy. I can easily put a sticky note through.



Is it safe to use? I've seen 3 different units of this popular model and all of them had a gap of some size.

[charles1948]

Burag, thanks for raising this question..

It has worried me in the past, about the possible leakage of microwave radiation from these ovens.
Not just from the cracks at the side of their doors, which you point out, but also from the glass screens on the front of their doors.

Many years ago, I decided to make a shield for my microwave oven. I did this by selecting a suitably-sized cardboard box, then lining the box's internal and outer surfaces, with sheets of aluminium kitchen-foil.

Then I put this box over the microwave oven, whenever it was switched on and operating.
However after doing this for a while, I stopped, and threw the box away.  Ever since, I've just used the "bare" oven.

But your remark about bread getting crisper, when you placed it outside the "crack" of the oven door, has disturbed me.  Not much -  but a bit.

Are you sure the bread didn't get crisper owing to exposure to the air, rather than to microwave radiation?

[evan_au]

in 10 minutes the bread became slightly more crispy.

But you know that you put the bread there.

You need a double-blind experiment:
- Have someone else put a slice of bread next to the door, and another slice in an equally hot location, with the same humidity, but far from the oven.
- Then have a third person (who doesn't know which is which) bring the two slices to you, and see if you can tell which is which
- Repeat at least 10 times, and see if your score is any better than pure chance.

By the way, for this to be meaningful, you need the microwave to be turned on for at least 10 minutes, with an absorbing substance inside (eg water or meat).
- The microwave, and the air exhausted from  the microwave gets pretty hot in 10 minutes.
- I think you are drying your bread in hot air, making it stale.

I can easily put a sticky note through.

It looks to me as if there is a tunnel around the hinge.
- This forms a bit of a transmission line, which absorbs microwaves with one polarization
- Normally, there is a seal which blocks microwaves with the other polarization

Are you sure that you are inserting the sticky not far enough to pass the seal?

the glass screens on the front of their doors.

If you look into the glass, you will see a mesh with holes punched in it.
- The size of the holes in the mesh (1-2mm) is much less than the wavelength of the microwaves (about 120mm at 2.5 GHz), so hardly any leaks through.

I would not be worried about new microwave ovens, as they are tested during manufacture.
- However, once you have been using them, regularly wipe around the seal to remove any food residue.
- If the seal is physically damaged, replace it.

If you are still worried, listen to COVID-19 advice: physical distancing by a couple of paces significantly reduces transmission!
       - However, a surgical mask won't help at all!

[wolfekeeper]

Microwave doors have a hidden seal around the edge; they're usually based on quarter wave Helmholtz anti-resonant slot.

What this does is ensure that there's a node all the way around the edge of the door, in other words there can be no microwaves at the edge of the door. This type of seal is highly insensitive  to small misalignments- unless the hinges are really badly broken and the door hanging off don't worry. Just because you can slide a piece of paper past the seal is not a concern.

Incidentally, if there really was somehow, magically, a BAD leak (which is essentially unheard of), you would burn your finger if you put it on the edge. Other than possibly a slight breeze- which may be warm from the air in the microwave being heated by the food, I really, really doubt you will feel anything at all.

[CliffordK]

EM radiation falls off by the square of the distance. 

I always take a step or two back whenever I put something in a microwave, and resist the temptation to put the nose up to the glass.

[charles1948]

EM radiation falls off by the square of the distance. 

I always take a step or two back whenever I put something in a microwave, and resist the temptation to put the nose up to the glass.

That's a wise precaution.  I also keep well away from my microwave oven when it's switched on and cooking.

This is because the microwave oven emits a disturbingly loud, almost aggressive, "roaring" noise while operating. Very different from old traditional gas or electric ovens, which cook silently, peacefully, and naturally.

The stark roaring of the new microwave oven, might indicate that something unnatural is going on.  Isn't that a good reason to adopt precautionary measures?

[vhfpmr]

the microwave oven emits a disturbingly loud, almost aggressive, "roaring" noise

That's the fan.

[charles1948]

the microwave oven emits a disturbingly loud, almost aggressive, "roaring" noise

That's the fan.

Is it?  I've got a 2KW electric fan-heater in my living-room. It makes hardly any noise.  No more than a gentle whisper.

Whereas the microwave oven in my kitchen makes a loud roaring-noise.

That can't come from the fan in the microwave-oven can it?  The fan is tiny!  How can it make so much noise?

[wolfekeeper]

The fan is used to cool the magnetron. It's more like a computer fan, it's removing heat from a relatively small component. Those types of fans generally are quite noisy.

[charles1948]

The fan is used to cool the magnetron. It's more like a computer fan, it's removing heat from a relatively small component. Those types of fans generally are quite noisy.

Thanks wolf for your reply.  But I'm a bit confused by your comparison between the fan used to cool the magnetron in a microwave oven,  and the fan used to cool a computer. 

The fan in the computer I'm using at this moment, is very quiet.  It makes only a low ""whispering" noise.
Nothing like as loud as the microwave-oven fan, which you say is used to cool the magnetron in the oven.

So, could it be, that the noise in the oven, comes not from the fan in it, but from the magnetron itself?

I'm pretty sure that must be right. But if so, why does the magnetron make a noise?

[vhfpmr]

why does the magnetron make a noise?

It doesn't. It's a thermionic valve, there are no moving parts.

[Bored chemist]

why does the magnetron make a noise?

It doesn't. It's a thermionic valve, there are no moving parts.

It has a large, rapidly varying current running through it, and a magnet wrapped round it.
Since it's not infinitely rigid, it will vibrate.

The power transformer feeding it will also make a noise.

[vhfpmr]

why does the magnetron make a noise?

It doesn't. It's a thermionic valve, there are no moving parts.

It has a large, rapidly varying current running through it, and a magnet wrapped round it.
Since it's not infinitely rigid, it will vibrate.

The power transformer feeding it will also make a noise.

Yes, but that's a hum, not a "roaring noise".

[charles1948]

I'd like to come back to this question - why do microwave ovens make a loud noise?

So far, I haven't seen any convincing answers.

[vhfpmr]

I'd like to come back to this question - why do microwave ovens make a loud noise?

So far, I haven't seen any convincing answers.

You've had the answer, you just don't want it. The fan makes a loud sound of rushing air, then there's a hum from the transformer and the solenoid around the magnetron.

If you switch the oven onto a reduced power you'll hear the timer clicking in and out as it reduces the duty cycle, and you'll hear the hum whilst the magnetron is running, but not when the magnetron is off. Note how the "roaring noise" remains when the magnetron is off: that's because it's coming from the fan and not the magnetron.

[Bored chemist]

So far, I haven't seen any convincing answers.

It is not the answers' fault that you are not convinced.

[evan_au]

why do microwave ovens make a loud noise?

Food sometimes gets very hot in one location, and produces a small steam explosion, spraying bits of food around the inside of the microwave.
- I usually put a loose lid or plate over the top of the food to stop it splattering on the inside of the microwave.

Warning: Do not put a sealed, airtight container in the microwave! That will make a loud noise (but just once...)

[charles1948]

So far, I haven't seen any convincing answers.

It is not the answers' fault that you are not convinced.

I'm not convinced  -  because I'm in the presence of two electrical appliances:

1.  The computer I'm typing on
2.  A 2KW electric heater warming the room

Both these have fans, which are whirring away.

Yet the noise from their fans, combined, is nothing like as loud as the noise emitted by my microwave oven, in the kitchen, when it's switched on.

So, sorry, I don't buy the idea that it's just the single little fan in the microwave that makes the loud noise.

I reckon it's obviously the magnetron in the oven that does it. 

What I'm seeking is an explanation of how it does it.

[Bored chemist]

If the heater or computer made that much noise, you wouldn't have bought them.
But it's not important for a microwave because you only need to put up with it for a few minutes.
So it's not worth the trouble and expense of using a quiet fan.

[Bored chemist]

What I'm seeking is an explanation of how it does it.

It has a large, rapidly varying current running through it, and a magnet wrapped round it.
Since it's not infinitely rigid, it will vibrate.