To nuke or not to nuke

SHMBO often heats plates in the microwave. She places a little water on them and hits them with a 100% blast of whatever is in the microwave. She has done this for many years and in fact for many years with the plate shown below, and it's mates of course. We have had this crockery for at least twelve years.

However the other day something different occured. Either insufficient water or too long a nuke time or fatigue resulted in the plate developing a little volcano (I was going to say nipple but that probably would have been deleted) in the centre of the plate on both sides.

This deformation is almost central. In fact the third picture is of the plate spinning, not that you can see it:rolleyes:. Just rotating it by hand it will spin for over three minutes.

I have several questions as a result of this phenomena (the damage to the plate not the spin time:D)

1. What has caused this rupture of the plate to occur and also why after all this time?

2. If microwaving does this to the plate, what does it do to the food and is it truly safe?

3. The plate has a checkered pattern on the perimeter and when spun appears to rotate in the opposite direction to that in which it was spun. Wheels on vehicles appear to do this too. I appreciate it is an optical illusion, but what really happens?

Just on the second point I have a naturapth friend, who maintains that micowaved food when placed under a microscope has changed dramatically compared to coventionally heated foods.

Interested to hear your thoughts.

Regards
Paul

I'm not 100% sure, but over time there may have been a crack in the glazing of the plate, which has allowed water in under the glazing. When the microwave heated it, the water inside expanded, causing the bubble.

Microwaves work by producing electromagnetic radiation of a wavelength that excites water molecules, heating them up (and therefore indirectly heating up the surrounding stuff that contains the water). You can get an idea of the actual wavelength, as the holes in the grill over the front door are a little smaller than the microwaves' length. Your naturopath friend was right in that heating food by any means will permanently alter it chemically, but there is nothing 'special' about microwave radiation; it is a a lot shorter wavelength than radio waves, a bit shorter than tv signals, a bit longer than infrared radiation, a fair bit longer than visible light, and a lot longer than UV (all of which are forms of EMR).

As to the third point, I hope someone else can say, because I would love to know too.

1. Be thankful it stayed in one piece and didn't take out the microwave. It might have if left longer and that pimple burst. I once saw the after effects of a superheated air bubble in the base of a (well used) ten litre cooking pot full of spag bog. The only part of a domestic kitchen untouched was above the fridge directly opposire the stovetop.

2. A few weeks ago, a listener claimed an ABC talkradio host was dangerous in her support for microwave cooking (and challenged her to mention it on air). In return she very effectively took apart the anti-microwave every claim the listener had quoted and included references. I think she lost a fan.

3. Stroboscopic effect
Stroboscopic effect - Wikipedia, the free encyclopedia
I can't remember all the intracacies but they can be fun. It also has a practical use, or once did. Some gramophone disc manufacturers used to incorporate them into the disc label. The listener would use the pattern to set the speed for that record's playback. Too fast - it moved one way, too slow - the other way, just right - stationary. I've even seen it on more modern B&O turntables.

A quick search of the interwebs reveals a lot of articles on the dangers of microwaves but mostly on sites that believe in UFO's or homeopathy. :)

Thank goodness this topic has at last come up as it will prove to my wife that I am not the only one who lies awake at night thinking about these gadgets. At this early stage, my obsession is centred around the fact that the turntables of all microwaves seem to rotate exactly a whole number of revs in one minute so that the handle of the cup is facing you when it finishes if you press a whole number of minutes. Ours does 5 RPM, my son's does 6, a friend's does 4. So I now know my 12 times table - pressing 36 secs or 48 or whatever so that the handle faces me when it's finished. Tomorrow I must get a life.

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Originally Posted by Bushmiller

However the other day something different occured. Either insufficient water or too long a nuke time or fatigue resulted in the plate developing a little volcano (I was going to say nipple but that probably would have been deleted) in the centre of the plate on both sides.

This deformation is almost central. In fact the third picture is of the plate spinning, not that you can see it:rolleyes:. Just rotating it by hand it will spin for over three minutes.

I have several questions as a result of this phenomena (the damage to the plate not the spin time:D)

1. What has caused this rupture of the plate to occur and also why after all this time?

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water penetration of a microcrack in the glazing.
the microcrack most probably developed through handling of teh plate and/or using the dishwasher

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2. If microwaving does this to the plate, what does it do to the food and is it truly safe?

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as most know water is that nasty chemical called H2O. Radiation at the right wavelength causes the water molecules to vibrate. The greater the vibration the "hotter" the water molecule gets. This heat is transferred to the food.

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3. The plate has a checkered pattern on the perimeter and when spun appears to rotate in the opposite direction to that in which it was spun. Wheels on vehicles appear to do this too. I appreciate it is an optical illusion, but what really happens?

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light from AC power sources pulses 50 times per second -- think of a strobe light flashing 50 times per second
your brain interprets the flashes as being a constant light -- but when you get a pattern spining at the right speed the flashes will either make the pattern appear to stand still or spin backwards

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Originally Posted by dabbler

1. Be thankful it stayed in one piece and didn't take out the microwave. It might have if left longer and that pimple burst. I once saw the after effects of a superheated air bubble in the base of a (well used) ten litre cooking pot full of spag bog. The only part of a domestic kitchen untouched was above the fridge directly opposire the stovetop.

.

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It is more likely water that penetrated a crack or tiny hole. Air rarely cases anything to explode cos its pretty good at compressing. But when water boils it suddenly all turns to gas and does a really good job of propelling things across rooms, or pushing trains up hills.

How it has actually grown a lump in the plate is a bit weird. I have seen pottery do that in the firing. But not years after like that. Perhaps there is some iron in the clay body that cased that local bit of clay to get even hotter and distort. Why its not cracked apart is also a mystery. I guess the stresses were able to go out into the bubble rather than sideways in the plate. :think:

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Originally Posted by snowyskiesau

A quick search of the interwebs reveals a lot of articles on the dangers of microwaves but mostly on sites that believe in UFO's or homeopathy. :)

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No problems, provided you are wearing your foil hat. :D

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Originally Posted by snowyskiesau

A quick search of the interwebs reveals a lot of articles on the dangers of microwaves but mostly on sites that believe in UFO's or homeopathy. :)

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Or naturopaths

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Originally Posted by Bushmiller

Just on the second point I have a naturapth friend, who maintains that micowaved food when placed under a microscope has changed dramatically compared to coventionally heated foods.

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That's it - I'm getting rid of my microscope immediately as they are obviously dangerous :wink:

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Originally Posted by snowyskiesau

A quick search of the interwebs reveals a lot of articles on the dangers of microwaves but mostly on sites that believe in UFO's or homeopathy. :)

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I still don't know what a homeopath is. Sounds like a gay serial killer.

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Originally Posted by pugwash

I still don't know what a homeopath is. Sounds like a gay serial killer.

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That cracked me up. :roflmao:

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Originally Posted by pugwash

I still don't know what a homeopath is. Sounds like a gay serial killer.

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I'm guessing you wouldn't be overly receptive to a holistic approach either:p.

Regards
Paul

How microwaves work (physics equation version):

"The water dipole attempts to continuously reorient in electromagnetic radiation's oscillating electric field. Dependent on the frequency the dipole may move in time to the field, lag behind it or remain apparently unaffected.
When the dipole lags behind the field then interactions between the dipole and the field leads to an energy loss by heating, the extent of which is dependent on the phase difference of these fields; heating being maximal twice each cycle."

http://www.lsbu.ac.uk/water/microwave.html

Caution. Contains hard science content; may not be comprehendable by naturopaths, homeopaths, Reki practitioners, aura readers and other snake oil salesmen.

Nifty applet demonstrating it all: http://www.colorado.edu/physics/2000/applets/h2o.html

Thank you for all the input. Further theories most welcome.

It looks like the plate has developed a fault in the glaze and that has allowed water to be absorbed into the pottery itself. When it was heated it "blew" out the surface on both sides of the plate.

We only use the microwave to defrost food and almost never to cook. Occassionally we reheat foods such as bolognaise sauce. I suppose using the microwave is not an earth shattering issue for us. We still have plenty of plates to go yet :wink:.

I have heard of microwave disasters with foods such as eggs (still in the shell) and potatoes still in their jackets.

I like Bob's approach. I'm ahead of him there as I don't have a microscope to cast out. (I'm thinking you might have been a fan of The Far Side.)

Back to the lesser issue of the spinning plate, it definitely appears (is that an oxymoron) to change direction as it slows down. I'm not sure why my brain (even allowing for it's diminutive size and largely unused condition) would assess the direction in reverse to what it knows is happening.

Life's a mystery, but only on the good days:).

Regards
Paul

Change in direction of the plate is due to the interaction of the pattern on the plate and the 50 Hertz flicker of the light.

Stroboscopic effect - Wikipedia, the free encyclopedia

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Originally Posted by Farmer Geoff

. At this early stage, my obsession is centred around the fact that the turntables of all microwaves seem to rotate exactly a whole number of revs in one minute so that the handle of the cup is facing you when it finishes if you press a whole number of minutes........................... Tomorrow I must get a life.

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The latest type of microwave doesn't have a turntable, you just put the cup in it and it stays in position. So upgrade and it will help you to get a life. :U


Peter.

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Originally Posted by Master Splinter

Change in direction of the plate is due to the interaction of the pattern on the plate and the 50 Hertz flicker of the light.

Stroboscopic effect - Wikipedia, the free encyclopedia

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MS

I was about to do the smart **se thing and say that this obviously doesn't apply in countries that generate at 60Hz, but of course it does, although at a slightly higher speed.

Thanks to physicists MS and Ian, potter TL and all the other miscreants for an entertaining way to learn.

Regards
Paul

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Originally Posted by Bushmiller

MS

although at a slightly higher speed.

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and in the opposite direction in the northern hemisphere :wink:

The serious bit about the stroboscopic effect is that rotating objects such as lathes & router cutters can appear stationary under fluoro lights. Don't know if I'm correct in thinking that incandescent light used to be required in industrial situations.

I was concious of the effect when I put lights in my shed, but no matter how I tried I could not reproduce the effect on routers, drills, circular saws and other rotating objects. I put them in good lighting (fluro spotties) and ran them through their speed ranges but nothing was evident.

I suspect that not only does the light need to be quite strong and but there also needs to be good contrast between the teeth, blades etc and the background to produce the effect which is why the little discs in the centre of turntables work as they have black and white segements and I supose the internal lighting is strong enough.

A mate of mine used to run a large industrial fabricating establishment and he was very aware of it as an OH&S issue

Ian

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Originally Posted by Ian Smith

I was concious of the effect when I put lights in my shed, but no matter how I tried I could not reproduce the effect on routers, drills, circular saws and other rotating objects. I put them in good lighting (fluro spotties) and ran them through their speed ranges but nothing was evident.

I suspect that not only does the light need to be quite strong and but there also needs to be good contrast between the teeth, blades etc and the background to produce the effect which is why the little discs in the centre of turntables work as they have black and white segements and I supose the internal lighting is strong enough.

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One thing that people forget is that there needs to be very tight synchronization between the 50 Hz of the lighting and a low multiple integer of the RPM of the rotation but there are not many small motors that synch with the 50Hz. For example 50Hz should equate to 3000 rpm for a two pole motor but a more likely RPM is ~2800 rpm

In addition, if there is any illumination by refection or other lights the effect is greatly diminished.

I'm not mechanically talented, unless a push bike counts, so I may be barking up the wrong tree, but isn't a timing light using this phenomena?

Yes

And this is just a freaky example of the effect....

[ame=http://www.youtube.com/watch?v=LVwmtwZLG88]curious stroboscopic effect - YouTube[/ame]

I've seen it demonstrated with an adjustable strobe light, and also seen it as a router slowed down under fluoros, but you wouldn't have mistaken that for one standing still.

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Originally Posted by Master Splinter

And this is just a freaky example of the effect....

curious stroboscopic effect - YouTube

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In addition to a stroboscopic effect, that particular effect is due to the rolling shutter effect which is also the reason the photo finish photos are distorted.

I have a turntable for playing vinyl records (remember?) that has a series of little checker patterns around the edge and a speed adjusting knob. You put the platter on, place the tone arm on the record and then adjust the speed until the pattern appears to stand still, and there you go , precisely 331/3 RPM. Completely useless really.

The Straight Dope: How come the wheels of a moving car appear to rotate backward sometimes?

Far more reliable source than wikipedia...

Melamine based eating ware is NOT microwave safe. It seems that water (or something) is caught in its structure & is heated preferentially by the microwave - I've seen soup in contact with a melamine bowl boiling around the edge while the middle of the soup, away from the plastic but still exposed, was cool to the touch.

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Originally Posted by Farmer Geoff

At this early stage, my obsession is centred around the fact that the turntables of all microwaves seem to rotate exactly a whole number of revs in one minute so that the handle of the cup is facing you when it finishes if you press a whole number of minutes. Ours does 5 RPM, my son's does 6, a friend's does 4. So I now know my 12 times table - pressing 36 secs or 48 or whatever so that the handle faces me when it's finished. Tomorrow I must get a life.

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Might want to look a little closer Geoff. My mug in the microwave ends up just about anywhere, and it's a pretty old microwave. I know that a lot of the new ones now return the turntable to the same positiopn that it started in once the mocrowaving has finished. Have a look and see if yours is one of those, or just a smarter one than mine.

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Originally Posted by Ian Smith

I was concious of the effect when I put lights in my shed, but no matter how I tried I could not reproduce the effect on routers, drills, circular saws and other rotating objects. I put them in good lighting (fluro spotties) and ran them through their speed ranges but nothing was evident.

I suspect that not only does the light need to be quite strong and but there also needs to be good contrast between the teeth, blades etc and the background to produce the effect which is why the little discs in the centre of turntables work as they have black and white segements and I supose the internal lighting is strong enough.

A mate of mine used to run a large industrial fabricating establishment and he was very aware of it as an OH&S issue

Ian

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I think that twin fluoro setups now are set out of phase with each other, so the strobe effect is avoided. Heard that somewhere but I'm no expert.