Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Nelson Ramphele on 26/11/2011 11:01:02
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Nelson Ramphele asked the Naked Scientists:
Hi Chris
I would like to know if there is any harmful effects caused by microwaves, every time micro oven is used to warm/heat up the food.
Thank you
Nelson
What do you think?
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Definitely, they make it easy to produce tasty meals hence you get too fat!!
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if you were exposed to the level of microwaves that exist in a microwave oven it would be harmful and could kill you. I am aware of a story that deep in the early days of microwaves someone in the USA managed to override the interlocks on a very early microwave and operate it with the door open stand right by it and cook himself with nasty fatal results.
The walls of microwave ovens are solid metal or screens with holes far to small for the microwaves to get out. The glass window prevents you for getting too close to the holes where the field is slightly stronger. The door of the microwave oven contains what is known as a "choke flange" this, by creating an out of phase reflection from a short circuited waveguide produces the effect of a solid metal contact right round the edge of the door and prevents the microwaves escaping from the small gap between the door and the body of the microwave just as if the waves were contained in a solid metal cavity
The design of the oven contains several fail safe interlocks that prevent microwaves being generated when the door is open. (unless someone goes to quite extreme measures to override these interlocks. if you operate microwave ovens in the vicinity of short range radio devices that use the same frequencies (various radio links for TV signals and broad band) you do suffer interference but these signal levels are much lower than mobile phone signals and quite safe.
Final testing procedures measure leakage (which is measurable) to ensure that everything is OK.
As for using microwaves (or any radio frequencies) to cook food the only effect is just the same as heating the food and no harmful reactions can take place and no residual radiation is left.
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You absolutely cannot be harmed by any microwave energy leaking from a door - that's likely to be less than 1 milliwatt / cm2. The threshold for feeling warmth from microwaves is 20 - 30 milliwatts / cm2 - I gave the keynote address on this topic in France in September at a major European microwave science conference.
I've deliberately exposed my arm, several times, to 10 kilowatts in an industrial microwave applicator - my arm got warm, then hot and became uncomfortable hot - when I pulled out of the applicator, there was no redness and no injury. So, the story of someone cooking himself by removing the oven door isn't true - the person would have felt so much heat, and possibly burned himself - the skin and maybe some muscle, but by them the pain would have been intolerable.
I'm a microwave scientist with 50 years of microwave heating experience.
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"I'm a microwave scientist with 50 years of microwave heating experience."
In any event, there's a world of difference between an arm (which has a good blood supply and is composed of tissues that are relatively robust) and other tissues- such as the eyes and gonads.
I accept that, from a few metres away the radiation from a microwave oven, even if the door were open, would not reach the legal limits, but it's still foolhardy to make such broad statements as you have done without qualifying them.
No name calling, please. Personal attack removed. -mod
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Microwave guru what you did was VERY dangerous but you got away with it. The cornea of the eye is the most sensitive part of the body and can be damaged at a few milliwatts per sq cm particularly at the higher microwave frequencies. I take it that your arm would be OK because you would feel hot but your intestines do not have heat sensors and the person was standing close to the open door of a working microwave cooker exposing his guts directly to the energy. The energy deposition is around half a wave or a few centimeters inside the skin and he cooked his guts. However he did not realise this for a few days until they fell apart and he died rather nastily of peritonitis.
However I would stress that modern microwave cookers used as instructed and unmodified are perfectly safe.
I have been involves with quite a fair bit of research and deveolpment on microwaves for all sorts of applications including cooking. . The tastiest way of cooking a tidy rolled joint of meat is to use ordinary short wave radio frequencies inside a pair of capacitative plates we had quite a few good meals investigating that technique its funny how the experiments always finished around lunchtime [:)]
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One of the things that might come up would be a historical thing about pacemakers and microwave ovens.
Notes indicate that since pacemakers and microwaves were introduced 30 to 50 years ago, they both have been given better shielding for their electronics. At least the pacemakers get updated once a decade or so, so you won't encounter anybody with a 50 year old pacemaker still ticking away.
There haven't been any major incidents of cardiac arrest attributable to pacemakers and microwaves. So, such warnings about microwaves and pacemakers are pretty much obsolete.
Another thing to keep in mind is distance.
As with any type of radiation, microwave EM radiation drops off with the square of distance.
So, if you have your nose, 1" from the microwave, you will get a certain amount of escaped EM radiation. Your ears might be 3" further away, and would get about 1/9 the dose of your nose.
If you stand back, say 20" the dose would be 1/400th of what it was at 1".
If you walk into another room, the dose falls off even further.
Personally, I like to take a step back from the microwave, or walk away from it while it is chugging away.
Years ago, I worked in a factory that had an "RF Machine" to dry wood glue. Essentially a big industrial microwave. On the side of the machine, they had a fluorescent lightbulb sitting on a rack without wires. It would light up due to RF emissions when the machine was on. I always liked to stand a bit away from that machine, although nobody seemed too concerned about it. I've tried the fluorescent bulb near an ordinary household microwave without any luck.
Anyway, I'd encourage taking an extra step backwards, but otherwise, concerns over microwaves are over rated, and the risk is likely less than that of using a cell phone.
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Well, it is safe to health if you read the owner manual and instructions! I think several precautions should be taken that may be mentioned in the instruction manual!
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It is interesting to consider how much change there has been in both microvave oven, and cell phone technology in the (almost) five years between #6 and #7.
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None in either case. I bought my microwave in 1987 and my mobile in 2002.....
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Microwave I can understand - but mobile? What's the matter with flags?
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Whats flags?
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Er - Semaphore? [:)]
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As with any type of radiation, microwave EM radiation drops off with the square of distance.
This is true of "far-field" electromagnetic radiation which has been emitted by the device and will propagate away to infinity (if it isn't absorbed by someone standing too close).
However, there are also "near field" electromagnetic fields which typically occur within a wavelength of the device, and can be much stronger than you would expect from the far-field measurements. So when you get within a wavelength of the grill in the door, the electromagnetic energy is much stronger than you would expect from the inverse square law.
As another post mentioned:
The glass window prevents you for getting too close to the holes where the field is slightly stronger.
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Er - Semaphore? [:)]
LOL. I wasn't too sharp yesterday......
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Probably the most dangerous aspects of a modern microwave are:
- You can burn your mouth on food that is too hot (a risk with all ovens, not specific to microwave ovens)
- The microwave energy is not evenly distributed, so some parts of the food may be fully cooked (even burnt!), while other parts are still frozen. This could leave pathogens alive in the food, causing food-borne illness.
- You can superheat water, and it explodes into steam when you drop in instant coffee grains.or a teabag
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Microwave ovens should be safe like and mobile phones
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Nelson Ramphele asked the Naked Scientists:
Hi Chris
I would like to know if there is any harmful effects caused by microwaves, every time micro oven is used to warm/heat up the food.
Thank you
Nelson
What do you think?
Virtually no harmful effects whatsoever.
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Probably the most dangerous aspects of a modern microwave are:
- You can burn your mouth on food that is too hot (a risk with all ovens, not specific to microwave ovens)
- The microwave energy is not evenly distributed, so some parts of the food may be fully cooked (even burnt!), while other parts are still frozen. This could leave pathogens alive in the food, causing food-borne illness.
- You can superheat water, and it explodes into steam when you drop in instant coffee grains.or a teabag
Those are problems with the cooking of foods in a mwo. Not dangers of the mwo itself. I think he's asking about radiation poisoning and damage which, of course, there are none.
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It depends what you are doing with it.
However, as long as whatever is in the microwave oven isn't alive...