I need some help with the physics of cooking, to be used when people start freaking out over the alleged danger of microwave ovens.
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It seems to me that hot food must be radiating into the infrared no matter how it was heated. In the case of microwave heating, a lower frequency is used to stimulate a frequency in the food that is higher than the frequency used to induce it. Correct?
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A stove burner transmits heat by conduction and an oven does it by convection. But how is the heat generated in the first place? Does an electric oven use electricity to generate infrared in the heating element, whose energy is then transmitted by conduction or convection? Or is something else going on? The heating element turns red so it seems that radiation is being generated in the visible spectrum.
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Does a gas stove generate infrared at all, or is the heat purely the result of the chemical reaction that occurs when we burn the gas? Do the flames look blue because they're generating blue photons, or because they're reflecting the blue photons that were already bouncing around the room?
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Is cooking over a fire different from cooking with gas, in terms of chemical heat versus electromagnetic radiation? I assume that a different chemical reaction is involved, since we're burning different materials.
Thank you for your help.
Best Answer
Heated food emits radiation in the infrared, if it emitted radiation at higher/blue frequencies, it would be too hot to eat, (and burnt). The microwave radiation heats the water molecules in the food, to normal cooking temperatures. As regards frequency, here is a full explanation Microwave ovens
I would naturally agree that when you see a red element, it is hot enough to emit red photons. But when you see those cop reality shows where the helicopter's infrared camera spots the "bad hombre" hiding in the trees, this shows you that infrared is not visible to human vision.
Infrared radiation is heat, for cooking purposes, they are synonymous. The gas is blue because of the temperature it is at, which emits some light in the blue frequency of the electromagnetic spectrum. It does not reflect blue photons, it emits them. But the blue light you see is not necessarily the majority of the electromagnetic radiation, which is in the hard/impossible to see, infrared part of the electromagnetic spectrum.
Obviously, you won't cook anything without adding heat to it. If you boil it, it's heat transfer through convection, hot water swirling around it, heated by either gas or wood. Gas is cleaner and more controllable. If you fry it, it's conduction, the pan conducts the heat from the gas or woodfire through the pan and onto the steak on the pan. If you roast something over a fire, or in an electric oven, it is cooked by both radiation and convection of the hot air. Burning wood is a different chemical reaction than than burning gas.
From Cooking Temperatures