. Does microwave cooking break molecular chains? Does any recombination of ions take place in the food and, if so, is there a possibility of eating some type of toxin formed during cooking?
The answers to all of these questions are no. Microwave cooking merely heats the water molecules, which in turn heat the food. The only molecular rearrangements that occur are those that are caused by warming the food toward the boiling temperature of water. In fact, there is less chemistry done during microwave cooking than is done in a normal oven. For example, one of the problems with microwave cooking is that food doesn't brown because the high temperatures needed to chemically modify the food molecules (and cause browning) aren't reached in microwave cooking. So you shouldn't have any fear of food cooked in a microwave oven. The microwaves don't damage it any more than heating it in boiling water would.
. How does a microwave oven heat food?
A microwave oven uses a vacuum tube called a magnetron to create intense microwaves inside the cooking chamber. These microwaves are electromagnetic waves with a frequency of 2.45 gigahertz or 2,450,000,000 cycles per second. They are similar to normal radio waves, except that they have a higher frequency. Because of these microwaves, the electric field at any point inside the cooking chamber fluctuates back and forth 2.45 billion times each second. That means that an electrically charged particle at any point in the cooking chamber will be pulled first one way and then the other, back and forth 2.45 billion times each second. While water molecules aren't electrically charged overall, they do have electrically charged ends—one end is positively charge and the other is negatively charged. In the presence of the microwave radiation, these water molecules find themselves twisted back and forth very rapidly. As they twist, they rub against one another and friction heats them up. The water becomes hot and this hot water, in turn, cooks the food. Food that doesn't contain water (like salt or oil) won't get hot. Neither will food in which the water molecules can't turn (like ice or frozen food). That's why it's hard to defrost frozen food in a microwave.
. Why are you required to have an item in the microwave oven while it is operating?
When a microwave oven is cooking food, electrons move rhythmically back and forth inside the magnetron tube and create the microwaves. These microwaves flow through a metal pipe and into the cooking chamber, where they are absorbed by the water in the food and thus heat the food (the twisting back and forth of the water molecules, described elsewhere on this page, not only heats the food—it also absorbs the microwaves). If there is no food in the cooking chamber, the microwaves build up in the cooking chamber until they are so intense that large numbers of them flow backward through the pipe to the magnetron. These microwaves reenter the magnetron and disrupt the motion of electrons inside it. The magnetron begins to misbehave and can be damaged as a result. To avoid such damage, you want to be sure that there is something in the cooking chamber to absorb the microwaves before they return to the magnetron and cause trouble. In short, don't run the microwave empty for any long periods of time.
. During a total solar eclipse, does the moon make first contact with the sun on the eastern limb or the western limb? Can you explain this to me?
The moon orbits the earth from west to east. By that, I mean that if the earth were to stop turning, the moon would then rise in the west and set in the east. During a total solar eclipse, the moon is drifting directly in front of the sun. Since the moon moves from west to east, it will first block the western edge of the sun, the western limb. In contrast, during a total lunar eclipse, the moon is drifting into the earth's shadow. Since it is moving from west to east, its eastern edge will enter the shadow first.
. Is it possible to create a "fog" in a small enclosed area without using dry ice or ultrasound?
The two techniques you mention, dry ice and ultrasound, are both intended to make tiny droplets of water in the air, effectively producing an artificial cloud. While I can't think of any better ways to make such water droplets, I can think of ways to make fogs of other materials. Tiny particles of any clear material will work because what you are seeing is the random scattering of light as it's partially reflected from the front and back surfaces of clear particles. I'd suggest a chemical process that produces tiny clear particles. The easiest one I can think of is to place a dish of household ammonia (ammonium hydroxide—ammonia gas dissolved in water) and a dish of hydrochloric acid (hydrogen chloride gas dissolved in water, sold as muriatic acid by hardware stores) in your enclosed area. The two gases will diffuse throughout your enclosure and react to form tiny clear particles of ammonium chloride. The enclosure will fill with a dense white fog. The particles are so small, that they will remain in the air for a very long time, but they will eventually settle on surfaces and leave a white powdery residue. So, unlike a water fog, this chemical fog is a little messy. You shouldn't breathe the fog, either.
. How do color-changing eyeglasses work?
These eyeglasses are made from a special photochromic glass that contains about 0.01% to 0.1% silver halide crystals. These crystals are transparent and so small that they leave the glass almost perfectly clear. But when the glasses are exposed to bright sunlight, which contains substantial amounts of ultraviolet light, the silver ions in those crystals are reduced to silver atoms and begin to form tiny silver particles inside the glass. Like the particles that form in black and white photography, these silver particles are so jagged and imperfect that they're light absorbing rather than shiny. The glasses thus darken when exposed to sunlight. But when the eyeglasses are returned to the dark, the halogen gas atoms recombine with the silver atoms and reform the silver halide crystals. The eyeglasses once again become clear. Incidentally, the glasses can also be rendered clear by exposing them to elevated temperatures, so a short time in the oven should help to clear them up if darkness alone doesn't do the trick. That assumes, of course, that you don't melt the frames, overheat the glass, or expose the glass to sudden thermal shocks.
. What would happen if you saturated the uranium side of a fusion bomb with cobalt? I think it would destroy our planet.
A fusion bomb, also known as a thermonuclear or hydrogen bomb, releases enormous numbers of fast-moving neutrons. Neutrons are uncharged subatomic particles that are found in the nuclei of all atoms except the normal hydrogen atom. A normal cobalt nucleus contains 32 neutrons and is known as cobalt 59 (for its 59 nuclear particles: 32 neutrons and 27 protons). When a neutron collides with a cobalt 59 nucleus, there is a substantial probability that the cobalt 59 nucleus will capture it and become cobalt 60 (for its 60 nuclear particles: 33 neutrons and 27 protons). Cobalt 60 is radioactive—it falls apart spontaneously with a 50% probability each 5.26 years. When a cobalt 60 nucleus decays, it begins by emitting an electron and an antineutrino to becomes nickel 60 (for its 60 nuclear particles: 32 neutrons and 28 protons). But this nickel 60 has extra energy in it and it soon emits two high-energy gamma rays (electromagnetic particles, with more energy than x-rays) to become normal nickel 60, a common form of the nickel atom. A fusion bomb containing cobalt 59 could be expected to make lots of cobalt 60, which would then undergo this radioactive decay over the next few decades, releasing gamma rays as it does.
So a fusion bomb containing cobalt would release a large amount of cobalt 60 into the environment. This would certainly give the bomb long lasting radioactive fallout that would make it much more damaging to the environment than a pure fusion bomb would be. Whether it would destroy the planet, I can't say. The bomb's explosion wouldn't be any more destructive, but its long-term toxic effect to animals and plants certainly would be.
. What is the difference between a fruit and a vegetable?
A fruit is the ripened ovary of a flowering plant, often with a woody stem, while a vegetable is the edible product of a herbaceous plant (a plant with a soft stem).
. Why is steam so efficient when cooking food and can you explain how so much heat is released when the steam changes phase, i.e. condenses?
Steam is the gaseous form of water and consists of independent water molecules. When steam comes in contact with relatively cool food, the water molecules have the opportunity to stick to one another and the steam condenses into liquid water. While most small molecules bind relatively weakly to one another, water molecules bind remarkably strongly. They form hydrogen bonds, in which negative charge on the oxygen atom of one water molecule attracts positive charge on a hydrogen atom of another water molecule. Water's hydrogen bonds are so strong that water remains a liquid well above room temperature while most other small molecules (carbon dioxide, methane, nitrogen, oxygen, etc.) are gases even at very cold temperatures. So when water molecules condense from steam to liquid, they form strong bonds with one another and release a great deal of energy. This energy takes the form of heat and it quickly raises the temperature of the food on which the water is condensing. That's why steam cooks food so quickly and efficiently.
. If microwaves "bounce" or reflect inside the cooking chamber, is it important for all of the surfaces (walls) of the oven to be flat? What would happen if the cooking chamber were cylindrical or circular? Would the microwaves bounce off the walls and then cancel each other out?
A microwave oven with a cylindrical or spherical cooking chamber would have a problem with non-uniform cooking. But before I look at why, I should note that even a microwave oven with a box-like cooking chamber exhibits non-uniform cooking. That's because the microwaves that are bouncing around inside the cooking chamber are all coherent—they are parts of a single, giant wave—and they can interfere strongly with one another. That means that several reflected microwaves can cancel or enhance one another as they cross, leading to regions inside the cooking chamber that cook quickly and other regions that cook slowly. That's why it's important to move the food around the cooking chamber during cooking—so that the food cooks evenly.
If the oven's cooking chamber weren't box-like, there would be a new problem to contend with: a tendency for the microwaves to be concentrated or focused in a particular region. Just as a cylindrical or spherical mirror bends the light rays it reflects, so the curved walls of a non-boxlike cooking chamber would bend the microwaves it reflects. It would tend to focus those microwaves in particular regions (such as the center of the cylinder or sphere) so that there would certain regions inside the chamber where the microwaves would be particularly intense and cooking would proceed very quickly.