What is the difference between a tube amplifier and a solid-state amplifier? Doe…

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What is the difference between a tube amplifier and a solid-state amplifier? Does the human ear prefer one over the other?

The only difference between a well-designed tube amplifier and a well-designed solid-state amplifier is the device doing the amplification. In fact, a vacuum tube and an metal-oxide-semiconductor field-effect-transistor or MOSFET are extremely similar in behavior, so that amplifiers built with the two devices can be extremely similar. If these amplifying devices are used properly in a good amplifier, that amplifier should only boost the power of its input signal and shouldn’t add anything that wasn’t present in the input signal. As a result, you shouldn’t be able to tell whether the audio amplifier you are listening to is based on tubes or on solid-state components.

When you make a telephone call, you send an analog signal from your phone to a c…

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When you make a telephone call, you send an analog signal from your phone to a central station. Is this direct current or alternating current? How do you and your neighbors share the line?

When you are talking to a friend over the telephone, the telephone company uses a special power supply to send a constant (direct current) through your telephones. Your telephone and your friend’s telephone share this current so that if your telephone draws more, your friend’s telephone receives less. When you talk into the microphone of your telephone, the current your telephone draws fluctuates up and down with the air pressure fluctuations at the microphone. As a result, the current through your friend’s telephone fluctuates down and up, the reverse of the current fluctuations in your telephone. A speaker in your friend’s telephone uses these current fluctuations to recreate the sound of your voice. When there are other extensions active in your home, they are all sharing this current so that talking into one telephone causes sound to be reproduced in all of the other telephones, both in your home and in your friend’s home. While modern electronics have changed the telephone system extensively, so that this direct current sharing isn’t quite the reality it was 30 years ago, all of the complicated electronic circuitry works to simulate this same relationship.

If microwaves “bounce” or reflect inside the cooking chamber, is it important …

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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.

Why is steam so efficient when cooking food and can you explain how so much heat…

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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.

What would happen if you saturated the uranium side of a fusion bomb with cobalt…

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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.

How do color-changing eyeglasses work?

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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.

Is it possible to create a “fog” in a small enclosed area without using dry ic…

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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.

During a total solar eclipse, does the moon make first contact with the sun on t…

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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.

Why are you required to have an item in the microwave oven while it is operating…

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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.