Well, as I said before, ice cubes definately wont be affected by normal microwaves. The real question is that are ice cubes affected by the defrost cycle. We want to find out if the defrost cycle changes the frequency of the microwaves or merely the intensity.
Physical dimensions of the Magntron determine the frequency of opertion. I am pretty sure that a microwave has a single operating frequency. I was looking for a mechanism to explain the observations, given a single operating frequency.
The 'defrost' and other settings on a microwave oven don't alter the intensity of the microwave energy, instead they alter how long it is applied for.
At 'full power' the microwave generator is switched on continually during cooking. In 'defrost mode' it would be switched on for about 5 seconds, then switched off for 15, then on again. Different power levels control how frequently and how long for the generator is switched on.
There are significant difficulties in controlling power - although this may be possible on the new inverter driven microwave ovens. All the ovens I've seen use a single tapped transformer to power the magnetron, with a relay to switch it on and off. No way of controlling power other than by duty cycle.
Adjusting frequency is undesirable and highly impractical.
The lower power modes allow more time for heat to be conducted from the hot outside of the food into the centre.
At 'full power' the microwave generator is switched on continually during cooking. In 'defrost mode' it would be switched on for about 5 seconds, then switched off for 15, then on again. Different power levels control how frequently and how long for the generator is switched on.
There are significant difficulties in controlling power - although this may be possible on the new inverter driven microwave ovens. All the ovens I've seen use a single tapped transformer to power the magnetron, with a relay to switch it on and off. No way of controlling power other than by duty cycle.
Adjusting frequency is undesirable and highly impractical.
The lower power modes allow more time for heat to be conducted from the hot outside of the food into the centre.
Seeing as we can get microwaves down to $50 now, why wouldn't it be possible for higher end microwaves to just contain 2 magnetrons?
sao123
Lifer
- May 27, 2002
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Microwave resonance uses the polarity property of molecules to work.
I have provided an excerpt from a website i found below...
Here is my SWAG on the plate vs the froze food...
The molecules in your plate are more subject to polar vibrations than the ice crystals, which would be why the plate gets hotter faster than the ice. Ice crystals are heavily bonded, therefore they are less likely (comparitively) to have the polar vibrations. however once the plate hets hot, then that energy will be conducted to the frozen food, then once the thaw gets a foothold on the edge of the food nearest the plate, the process can begin to occur as it is supposed to.
excerpt provided.
The waves of microwave energy are cycling above and below a horizontal baseline. The half cycle below the baseline possesses negative properties, and the half cycle above the line is correspondingly positive. Basically, the effect of this wave, as it alternates between positive and negative, would be like a magnet flipping back and forth.
All liquids and food products are made up of molecules. These molecules have positive and negative particles, so they tend to behave like microscopic magnets. As the positive half cycle of the microwave penetrates the food, the negative particles of the molecules are attracted and attempt to align themselves with this positive field of energy. Then, when the microwave energy alternates to the negative half cycle, the opposite occurs -- The negative particles are repelled and the positive particles are attracted, causing a flipping motion (actually, this reaction is the movement of the particles within each molecule, so, technically, they reverse polarity). This might be compared to a room full of people trying to run back and forth, from one side to the other. Obviously, there would be a lot of bumping, rubbing, agitation, and friction.
Now, consider that the actual frequency of the RF energy used in microwave ovens is 2450 million cycles per second! Moreover, consider that within the course of one of those cycles, the molecules would actually change their direction (polarity) twice - once for the positive half-cycle and once for the negative half-cycle. This red-hot rate of vibration causes tremendous friction within the food, and - just as rubbing your hands together makes them warm - this friction produces heat.
So the heat is produced directly in the food, but the food is not cooked, as is commonly believed, from the inside out. Actually, the cooking begins just beneath the outer surface and from there inward and outward, with the majority of the energy being expended in the outer layers. The rate and degree of heating depend on the depth and density of the food, as well as its ability to conduct heat. Because the microwave energy is changed to heat as soon as it is absorbed by the food, it cannot make the food radioactive or contaminated. When the microwave energy is turned off and the food is removed from the oven, there is no residual radiation remaining in the food. In this regard, a microwave oven is much like and electric light that stops glowing when it is turned off.
I have provided an excerpt from a website i found below...
Here is my SWAG on the plate vs the froze food...
The molecules in your plate are more subject to polar vibrations than the ice crystals, which would be why the plate gets hotter faster than the ice. Ice crystals are heavily bonded, therefore they are less likely (comparitively) to have the polar vibrations. however once the plate hets hot, then that energy will be conducted to the frozen food, then once the thaw gets a foothold on the edge of the food nearest the plate, the process can begin to occur as it is supposed to.
excerpt provided.
The waves of microwave energy are cycling above and below a horizontal baseline. The half cycle below the baseline possesses negative properties, and the half cycle above the line is correspondingly positive. Basically, the effect of this wave, as it alternates between positive and negative, would be like a magnet flipping back and forth.
All liquids and food products are made up of molecules. These molecules have positive and negative particles, so they tend to behave like microscopic magnets. As the positive half cycle of the microwave penetrates the food, the negative particles of the molecules are attracted and attempt to align themselves with this positive field of energy. Then, when the microwave energy alternates to the negative half cycle, the opposite occurs -- The negative particles are repelled and the positive particles are attracted, causing a flipping motion (actually, this reaction is the movement of the particles within each molecule, so, technically, they reverse polarity). This might be compared to a room full of people trying to run back and forth, from one side to the other. Obviously, there would be a lot of bumping, rubbing, agitation, and friction.
Now, consider that the actual frequency of the RF energy used in microwave ovens is 2450 million cycles per second! Moreover, consider that within the course of one of those cycles, the molecules would actually change their direction (polarity) twice - once for the positive half-cycle and once for the negative half-cycle. This red-hot rate of vibration causes tremendous friction within the food, and - just as rubbing your hands together makes them warm - this friction produces heat.
So the heat is produced directly in the food, but the food is not cooked, as is commonly believed, from the inside out. Actually, the cooking begins just beneath the outer surface and from there inward and outward, with the majority of the energy being expended in the outer layers. The rate and degree of heating depend on the depth and density of the food, as well as its ability to conduct heat. Because the microwave energy is changed to heat as soon as it is absorbed by the food, it cannot make the food radioactive or contaminated. When the microwave energy is turned off and the food is removed from the oven, there is no residual radiation remaining in the food. In this regard, a microwave oven is much like and electric light that stops glowing when it is turned off.
I think i figured out the hot plate mystery.
The plates are very old and cracked. The clay absorbes lots of waters through the crackes in my dishwasher etc. but never really dries.
So it's the water in my plates that's being heated up. My new, non-cracked plates stay cool.
The plates are very old and cracked. The clay absorbes lots of waters through the crackes in my dishwasher etc. but never really dries.
So it's the water in my plates that's being heated up. My new, non-cracked plates stay cool.
keep in mind also, clay is heated to thousands degrees to remove moisture and harden, but that doesn't mean it can't absorb more moisture. Normal humidity will get moisture into ceramic items depending on the glaze used...if any...
sao123
Lifer
- May 27, 2002
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Are you sure that....
It couldnt possibly have anything to do with the fact that your "old" plates probably had a high content of SiO2 (Silicon Dioxide), A molecule which most glasses, ceramics, porcelines, and clays are mostly made of? SiO2 is highly polar in nature (similar to water molecule shape with + & - poles) and would heat up in the microwave due to the explaination i gave earlier.
Your "new" plates are probably made of a newer lighter material with much less concentration os SiO2, causing them to be less heated in the microwave.
IE: There is no water inside your plates, glass, or whatever.
It couldnt possibly have anything to do with the fact that your "old" plates probably had a high content of SiO2 (Silicon Dioxide), A molecule which most glasses, ceramics, porcelines, and clays are mostly made of? SiO2 is highly polar in nature (similar to water molecule shape with + & - poles) and would heat up in the microwave due to the explaination i gave earlier.
Your "new" plates are probably made of a newer lighter material with much less concentration os SiO2, causing them to be less heated in the microwave.
IE: There is no water inside your plates, glass, or whatever.
No I really think it was just the water sneaking in there. right after I pulled it from the dishwasher i could see obvious wetness around the cracks.
sao123
Lifer
- May 27, 2002
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I was being sarcastic (in case you couldnt tell by my tone)...
Your plate would become hot regardless if you ever washed it or not. Believe me it isnt the water.
The small amount of water which may or may not get into the cracks, is not enough to heat the entire plate evenly to that high of a temperature, especially since SiO2 is not a very good heat conductor...
Imagine a small amount of boiling water molecules heating an entire plate (1000x times the mass of the water) to a comparable temperature...the laws of conservation of energy disputes your claim.
Your plate would become hot regardless if you ever washed it or not. Believe me it isnt the water.
The small amount of water which may or may not get into the cracks, is not enough to heat the entire plate evenly to that high of a temperature, especially since SiO2 is not a very good heat conductor...
Imagine a small amount of boiling water molecules heating an entire plate (1000x times the mass of the water) to a comparable temperature...the laws of conservation of energy disputes your claim.
RelaxTheMind
Platinum Member
- Oct 15, 2002
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DrPizza
Administrator Elite Member Goat Whisperer
Last summer, I saw a teacher do a demonstration where she lined the bottom of a microwave with mini marshmellows... She then turned the microwave on for 30 seconds or so. I was amazed that you could see the marshmellows form a wave shape due to the microwaves, and you could measure the wavelength of the microwaves.
The energy from the microwaves isn't distributed evenly throughout the microwave... there are hot spots and cold spots. Thus, with the ice cube experiment, it would be interesting to see what would happen if the ice cube was moved to a different location in the microwave. Furthermore, I'm curious as to what degree microwaves are reflected off the surfaces of various foods (if they are.)
And, to shed a little light on the ice-cube melting vs. heating soup problem... It takes FAR more energy to turn solid water to liquid water than it does to heat liquid water. I suggest doing an experiment to determine how much energy is absorbed by the soup in 2 minutes and how much energy is absorbed by the ice cube in 2 minutes. My speculation is that they're very similar.
And lastly, about ice: The nature of the water molecule H2O doesn't change! The microwaves are exciting the bonds between the hydrogen and oxygen. These bonds really don't change that much as water goes from liquid to solid. (speaking from the chemistry side of my head - speaking from the quantum mechanics side of my head, I'm not 100% positive)
The energy from the microwaves isn't distributed evenly throughout the microwave... there are hot spots and cold spots. Thus, with the ice cube experiment, it would be interesting to see what would happen if the ice cube was moved to a different location in the microwave. Furthermore, I'm curious as to what degree microwaves are reflected off the surfaces of various foods (if they are.)
And, to shed a little light on the ice-cube melting vs. heating soup problem... It takes FAR more energy to turn solid water to liquid water than it does to heat liquid water. I suggest doing an experiment to determine how much energy is absorbed by the soup in 2 minutes and how much energy is absorbed by the ice cube in 2 minutes. My speculation is that they're very similar.
And lastly, about ice: The nature of the water molecule H2O doesn't change! The microwaves are exciting the bonds between the hydrogen and oxygen. These bonds really don't change that much as water goes from liquid to solid. (speaking from the chemistry side of my head - speaking from the quantum mechanics side of my head, I'm not 100% positive)
sao123
Lifer
- May 27, 2002
- 12,653
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This is correct, the chemical form of water does not change...but the physical chemistry of the water does. (Do you understand physical chemistry vs chemical chemistry?)
However the formation of ice bonds the individual water molecules together tightly on all sides into a crystal-like structure. This limits the way the molecules are free to move. If they cannot align with the pulse of the microwaves, then less friction will occur inside the ice block. Then less heat will be created. The ice will take much longer to heat.
See, in liquid water, the molecules are not bonded tightly in a crystal-like structure, so more molecules and follow the pulse of the wave and it heats faster.
Study the physical structure of frozen water... see where the intermolecular bonds are.
Edit
Here is my analogy.
The Microwave - Imagine a room full of people. The room has 2 lights a red one and a blue one, only 1 light is on at a time. When the red light comes on, everyone is supposed to rotate 180 degrees to the right, and when the blue one comes on, everyone rotates 180 degrees to the left. The free standing people represent the water. The lights flash back and forth and the people rotate back and forth and the friction (people bumping each other) produces heat.
Now imagine ice - Everyone holds at least 1 persons hand, 50% hold 2 hands. Now try the red/blue light. not too many people can rotate as freely, less friction, less heating.
The holding of the hands represents the intermolecular bonds of ice not present in water. (These bonds do exist in liquid form just not as strong as in solid form) Holding hands restricts the amount of movement any single molecule can have.
Hope that explains it better.
Not necessarily...
If a small amount of trapped water were in the plate and being excited by microwaves, they would not leave the plate, but continue to heat the surrounding ceramics via microwave induced vibrations. This is a completely different phenomena from the boiling water experiment you describe, as the water no longer gains energy once you remove it from the heat source and pour it on the plate. The reference to conservation of energy, in this case, is irrelevant, as one case is acting like a continuous heat source and the other is a fixed amount of energy input to the system.
As for my own explanation, I would say trapped water certainly could play a part as well as the possibility of similar bond lengths in ceramics and water that respond to the particular microwave frequency used. The trapped water theory holds more water (pun intended) if you notice plates doing this after being washed or used for a long time without thorough drying (for glazed ceramics...a long time) where they did not originally behave this way.
True. It takes about 330 J to turn 1 gram of 273K ice to 273K water, whereas it takes only 4.18 J to heat a gram liquid water 1K higher in temp.
DrPizza
Administrator Elite Member Goat Whisperer
Yep, that part was write, but I was corrected on the 4th paragraph above. That's not correct. The necessary wavelength/frequency needed to excite the bonds in ice is different than in liquid water (from what I could find on the internet while researching it a little bit.)
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