Microwave Vs. Visible light Heating

In summary: People always tell me that microwave ovens heat food by exciting the water molecules in food. This is done by blasting food with 2.4 Ghz radiation, the people that say this, also say that the frequency that is used is critical because that frequency interacts with the water molecules. Some people say that this frequency, 2.4 Ghz, interacts with water molecules to heat food. However, this frequency is also used for wirelesscommunication, like wifi. That's a big question for me. If it heats our tissues, why are we using a different frequency for wireless communications? And why does visible light absorb so much at that frequency?
  • #1
MichaelsTech
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People always tell me that microwave ovens heat food by exciting the water molecules in food. This is done by blasting food with 2.4 Ghz radiation, the people that say this, also say that the frequency that is used is critical because that frequency interacts with the water molecules. I wonder why then we use that frequency for wireless communications, for instance wifi. If it heats our tissues.

My major question is how does a visible light laser heat tissue if it uses a very different frequency? Also, can exposure to non ionizing radiation cause a atoms electron to be dislodged making the atom a ion, leading to cancer?
 
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  • #2
It's not so simple as frequency = X means Y molecule will absorb it and become excited. Molecular absorption lines are very different than atomic absorption lines. There tend to be many of them, and, depending on the complexity of the molecule, there can even be a rough continuum of absorptions. So the physics is pretty complicated.

But, generally speaking, water molecules tend to absorb at those frequencies (e.g. 2.4GHz) better. That certainly isn't the ONLY frequency that water molecules will absorb though.

As far as wifi signals vs microwave ovens. A microwave oven generates standing waves inside which basically uses constructive interference to amplify itself so that it can heat up the objects inside. In addition, a microwave is MUCH higher power than a wifi router (wifi routers don't typically take 1200 watts), and it's waves are enclosed in a small space. A wifi source has a much much weaker power, and is spread over a much larger area so it won't "cook us from the inside".

Visible light is definitely absorbed by tissue. Can you see through your skin an muscle? You can't. This means that visible light is being absorbed all the time. You might notice bright sunny day, your skin starts to burn after a while. That's your skin absorbing the light from the sun.

A laser just focuses this energy into a very small area so it can do damage.

Lastly, non-ionizing radiation is defined as such that it doesn't break up atoms (it doesn't "ionize" them), so non-ionizing radiation is much less dangerous. However, in high enough doses, it might become dangerous. You probably don't want to stand right next to a radio tower's big antenna for very long, for example.
 
  • #3
MichaelsTech said:
People always tell me that microwave ovens heat food by exciting the water molecules in food. This is done by blasting food with 2.4 Ghz radiation, the people that say this, also say that the frequency that is used is critical because that frequency interacts with the water molecules.

There's nothing really special about 2.4ghz and heating food (that contains water) in a microwave oven other than the penetration depth cooks food fairly evenly at that wavelength, it's easy to shield/concentrate and it's in the ISM (Industrial, Scientific and Medical) band. Higher frequencies (10-100GHz) would be actually be absorbed better by water but would burn the surface of food before the middle was cooked.
 
  • #4
When my skin absorbs visible light, what is actually absorbing the photons, the nucleus, electrons, or both? Is it true that when the nucleus is put into a high energy state that it will dump energy as electromagnetic radiation? What is causing us to emit infrared light, the energy is to high in the atom and it needs to lose some?
 
  • #5
Most of the absorption and re-emission will be from molecules, not individual atoms, since you're made of molecules and such, not individual atoms!
 
  • #6
nsaspook said:
There's nothing really special about 2.4ghz and heating food (that contains water) in a microwave oven other than the penetration depth cooks food fairly evenly at that wavelength, it's easy to shield/concentrate and it's in the ISM (Industrial, Scientific and Medical) band.
That the 2.4 to 2.5 GHz band is one of the ISM bands precisely because of microwave ovens. Microwave ovens standardized on 2.45 GHz well before the frequencies around 2.45 GhZ were designated as one of the ISM bands. When the FCC and its international equivalents decided they needed to carve up the radio frequencies into regulated and unregulated chunks it would have been downright stupid to turn microwave ovens into regulated devices. They instead made that frequency band that surrounds that commonly used microwave oven frequency into an unregulated band.
MichaelsTech said:
When my skin absorbs visible light, what is actually absorbing the photons, the nucleus, electrons, or both?
Electromagnetic radiation is photons and nothing else. Low frequency radiation (up to low ultraviolet) is non-ionizing. High frequency radiation (high UV, X-rays, and lower frequency gammas) knocks electrons from atoms and molecules. So what? What's a lost electron or two? The problem is that this disrupts the complex molecules in your body. The charged molecules function differently, sometimes disintegrating, other times recombining. Ionizing radiation seriously messes with life at the biochemical level.

High frequency gammas are even worse. They can hit your nuclei.What about lower frequencies? That depends a lot on intensity. While microwaves are not ionizing radiation, you do not want to put your cat in the microwave. Ripping electrons from molecules isn't good for life. Neither is getting those molecules vibrating so wildly that they become cooked.

The difference between ionizing versus non-ionizing radiation is that ionizing radiation does minor damage even in small doses. Non-ionizing radiation in small doses is like a tiny puff of slightly warm air.
 
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  • #7
You could cook some things with visible light, but not water, since it's transparent, and only the surface of most meats and vegetables, since light won't penetrate very far (maybe a few millimeters) in most foods. Overall, not very useful compared to microwaves. That said, heat lamps are often used to keep catered foods warm, and that uses infrared and visible light.

Nonionizing radiation won't cause electrons to be dislodged. It will just cook you. But only if you are exposed to enough to really raise your temperature. You will feel it.
 

What is the main difference between microwave and visible light heating?

The main difference between microwave and visible light heating is the type of electromagnetic radiation used. Microwaves use longer wavelength radiation, which causes the water molecules in food to vibrate and generate heat. Visible light, on the other hand, uses shorter wavelength radiation and is primarily absorbed by the surface of the food, causing it to heat up.

Which type of heating is more efficient?

Microwave heating is generally considered more efficient than visible light heating. This is because microwaves directly target and heat the molecules in food, while visible light heats the surface of the food first, which then transfers heat to the rest of the food. Additionally, microwaves can penetrate deeper into food, allowing for more even heating.

Can both microwaves and visible light be used for cooking?

Yes, both microwaves and visible light can be used for cooking, although they are typically used for different purposes. Microwaves are commonly used for heating or cooking foods that contain a lot of water, such as soups or vegetables. Visible light is often used for baking or browning foods, as it can create a crispy exterior while keeping the interior moist.

Are there any safety concerns with using microwaves for heating?

There are some safety concerns with using microwaves for heating, such as the potential for uneven heating or superheating of liquids. It is important to follow the manufacturer's instructions and use microwave-safe containers to prevent accidents. Additionally, some research suggests that high levels of microwave exposure could potentially be harmful, so it is best to limit your exposure and use caution when heating food in microwaves.

Which type of heating is better for preserving nutrients in food?

Both microwaves and visible light heating have the potential to preserve nutrients in food. However, studies have shown that microwaves may be slightly better at retaining nutrients, as they cook food quickly and at a lower temperature compared to visible light. It is important to note that the cooking method and duration also play a significant role in preserving nutrients in food.

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