# The Naked Scientists Forum

### Author Topic: Microwave Death  (Read 12537 times)

#### Pumblechook

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• Posts: 569
##### Microwave Death
« Reply #25 on: 09/12/2007 15:12:58 »
Most things I cook are in flat rectangular trays.

#### another_someone

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##### Microwave Death
« Reply #26 on: 09/12/2007 15:28:42 »
Most things I cook are in flat rectangular trays.

There are two issues here.

Firstly, what matters is not the shape of the tray, but the shape and size of the individual pieces of food (you can put round meatballs into a flat tray, but they still remain round meatballs).

But the real key issue is not the shape, but the size.  Shape will have an effect on the evenness of the heat (the corners of a rectangular piece of food will heat more than the flat sides).  Whatever the shape, so long as the shape remains the same, the surface area will increase (or decrease) in proportion to the square of any one dimension, and that is the key issue.  So, if you half the dimension, you will reduce by a quarter the surface area, so if 12mm (6mm from each side, as there will be two opposite sides) represents 50% of the depth of the item, then the surface area will have been reduced to a quarter of what it was, but the overall power only reduced by 37%, so the average power density will still increased 47% (although, as I said, if one is dealing with more realistic shapes, then this only represents average power distribution, and the actual power distribution will be very much more uneven).

#### another_someone

• Guest
##### Microwave Death
« Reply #27 on: 09/12/2007 15:35:42 »
But as regards if there is any 'damage', (which many conclude is rubbish) to food from microwave cooking many foods may have been processed anyway in the factory with RF possibly with the deeper penetrating 915 MHz.

For processed foods, I have no doubt of that, but the premise here was with regard to loss of nutrients from fresh vegetables, where I doubt that would be applicable.

#### Pumblechook

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• Posts: 569
##### Microwave Death
« Reply #28 on: 09/12/2007 15:45:29 »
I will have to try putting sliced veg in front the satellite LNB. Do I have to wait for a cooking programme?

There are claims that microwave cooking is actually better......

In studies at Cornell University, scientists looked at the effects of cooking on water-soluble vitamins in vegetables and found that spinach retained nearly all its folate when cooked in a microwave, but lost about 77 percent when cooked on a stove.

#### Pumblechook

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• Posts: 569
##### Microwave Death
« Reply #29 on: 09/12/2007 15:49:29 »
Others conclude that overcooking or overboiling is the problem and nowt to do with microwaves per se.

http://news.bbc.co.uk/1/hi/health/3188558.stm

#### pirunner

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• Posts: 74
##### Microwave Death
« Reply #30 on: 09/12/2007 15:56:14 »
Yes, I think the problem on the stove comes from boiling in the veggies. This supposedly sucks all the nutrients out. Steaming is supposed to be better.

#### another_someone

• Guest
##### Microwave Death
« Reply #31 on: 09/12/2007 16:47:20 »
Others conclude that overcooking or overboiling is the problem and nowt to do with microwaves per se.

http://news.bbc.co.uk/1/hi/health/3188558.stm

Certainly, that would be my preferred theory.  The only real question in my mind is whether the nature of microwaves makes overcooking more probable than with some other forms of cooking.

#### another_someone

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##### Microwave Death
« Reply #32 on: 09/12/2007 17:10:33 »
I have just tried putting wet paper sheets between a satellite dish and the LNB. 3 wet sheets is enough to 'kill' the signal.  I think it has to be 4 - 6 dB down before it can't decode the digital TV.   So that suggests a 4 - 6 dB loss through only 0.3mm of wet paper.  I need the whole of a (dry) 20 mm catalogue to for the receiver to fail.  This is at 12GHz of course rather than 2.45.

Bear in mind that wet paper would be thicker than dry paper (the main issue is that the paper present a matrix to absorb the water, but the water also has volume of its own).

But more importantly, you are not measuring the loss of signal in the wet paper, you are measuring the reduction of transmission through the paper (i.e. one has to ask how much of the signal was reflected, rather than absorbed?).

#### Pumblechook

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##### Microwave Death
« Reply #33 on: 09/12/2007 18:02:17 »
Points agreed but I was surprised that only 3 wet sheets did the trick.  What is that about ..three sheets to the.... ?

I might do some more scientific tests one day.. I have a lot of RF test gubbins here.

#### The Naked Scientists Forum

##### Microwave Death
« Reply #33 on: 09/12/2007 18:02:17 »