Month: December 1996

Is the fact that the small magnetic fields generated by appliances change due to…

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Is the fact that the small magnetic fields generated by appliances change due to the alternating electric current the reason that EMFs may cause health problems? — MC, Independence, KS

I believe that the alternating nature of the electromagnetic fields around appliances is at least part of the reason they’re suspected of causing health problems. Since these fields are created by an electric current that alternates in direction, they alternate in direction, too. However, I have not seen any credible evidence for there being a relationship between these appliance-related fields and health problems, nor have I heard any sensible physical theory for such a possibility. On the contrary, I have read a number of compelling arguments for why the tiny electromagnetic fields around appliances should have no biological effects at all. I think that the worries about EMFs are unfounded.

Can plastic melt in a microwave oven? How does this process work? Can plastic bu…

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Can plastic melt in a microwave oven? How does this process work? Can plastic burn in a microwave oven? – HD

Most plastics are unaffected by microwaves and do nothing at all in a microwave oven. For them to absorb energy from the microwaves, the plastics must either conduct electricity or their molecules must undergo the twisting motions that water molecules experience in the microwave oven. There are a few conducting plastics and these may melt or burn in a microwave as the microwave electric fields propel electric currents through them. There are also some plastics that trap water molecules and these may also melt or burn as the water molecules gather energy from the microwaves. I suppose that there are also a few plastics that have polar molecules in them that respond to the microwaves the way water does. However, most plastics do none of these and only melt or burn if they accidentally come in contact with very hot food or pieces of metal that happen to be in the microwave oven.

What is a photoconductor?

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What is a photoconductor? — MN, Chicago, IL

A photoconductor is a material that behaves as an electric insulator in the dark but becomes an electric conductor when exposed to light. An insulator is unable to transport electric charges because its own electrons can’t respond to modest electric forces. Because of quantum physics, electrons can only follow specific paths called “levels” as they move through a material and all of the easily accessible levels in an insulator are completely filled. For reasons of symmetry, there are always as many electrons traveling to the right in an insulator as are traveling to the left, so that on average, no electrons move anywhere, even when they are exposed to electric forces. But when light energy shifts some of the electrons from the filled levels to a collection of formerly unoccupied levels that previously weren’t accessible, these shifted electrons can respond to electric forces and transport electric charge through the material. In the light, a photoconductor stops acting as an insulator and starts acting as a conductor. Such photoconductors are the basis for xerographic copiers and laser printers.

How does a Bourdon tube pressure gauge work? – AM

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How does a Bourdon tube pressure gauge work? – AM

A Bourdon tube pressure gauge works on much the same principle as a party favor that inflates and unrolls when you blow in its tube. The hollow Bourdon tube of the pressure gauge isn’t circular in cross-section—it’s somewhat oval. When the pressure inside the tube increases, the tube’s oval walls are distorted and the tube’s cross-section becomes slightly more circular. However, the tube is wrapped in a coil and as its walls become more circular, the tube uncoils slightly. The amount of uncoiling that occurs is almost exactly proportional to the pressure inside the Bourdon tube. As the tube uncoils, its motion activates a rack-and-pinion gear system that turns the needle on the pressure dial of the gauge. While all that you see when you look at the gauge is this needle pointing at the current pressure, you should understand that there is a small, bent tube that’s coiling and uncoiling with each change in the pressure inside that tube.

What is gravity and how do you define it?

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What is gravity and how do you define it?

There are two levels at which to work. First, there is Newtonian gravity—an attraction that exists between any two objects and that pulls each object toward the center of mass of the other object with a force that’s equal to the gravitational constant times the product of the two masses, divided by the square of the distance separating the two objects. For example, you are attracted toward the earth’s center of mass with a force equal to the gravitational constant times the product of the earth’s mass and your mass, divided by the square of the distance between the earth’s center of mass and your own center of mass. This force is usually called “your weight.” The earth is attracted toward your center of mass with exactly the same amount of force.

Second, there is the gravity of Einstein’s general relativity—a distortion of space/time that’s caused by the local presence of mass/energy. Space is curved around objects in such a way that two freely moving objects tend to accelerate toward one another. As long as those objects aren’t too large or too dense, this new description of gravity is equivalent to the Newtonian version—they both predict exactly the same effects. But when one or both of the objects is extremely massive or very dense, general relativity provides a more accurate prediction of what will happen. In reality, mass/energy really does warp space/time and general relativity does provide the correct view of gravity in our universe. The next level of theory, quantum gravity (which will reconcile the theory of general relativity with the theory of quantum physics), is still in the works.