Author: Lou Bloomfield

How does heat affect magnetism?

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How does heat affect magnetism? — MC, Capitol Heights, MD

The magnetism we associate with a permanent magnet or with steel’s response to that permanent magnet involves the careful ordering of tiny magnetic electrons within the materials. Just as heat tends to destroy all forms of order in a newspaper when you put it in the fire, so heat tends to destroy the magnetic order in a permanent magnet or in steel when you bake them. Many permanent magnets lose their magnetism when heated to oven temperatures and even steel becomes non-magnetic when heated red-hot.

How can I make 1000 nanometer light waves visible to the human eye?

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How can I make 1000 nanometer light waves visible to the human eye? — DMB, Broken Aarow, OK

Although our eyes are insensitive to 1000 nanometer infrared light, there are two ways to detect it effectively. The easiest is to use an inexpensive black-and-white surveillance video camera. Many of these cameras are sensitive to a broader spectrum of light than are our eyes and they can see 1000 nanometer light. If you check around, you should be able to find one that sees the light you’re interested in. The other technique is to use a phosphorescent or “glow in the dark” material. When exposed to visible light, the atoms in such a material become trapped in electronic states that can emit visible light only after a very long random wait. But exposing a phosphorescent material to infrared light can shift the states of the atoms in the material to new states that can emit light immediately. Thus exposing some phosphorescent materials to infrared light causes them to emit light promptly. You can then see these materials glow particularly brightly after storing visible light energy in them and then exposing them to infrared light. However, they’ll only glow briefly before you have to “recharge” them by exposing them to more visible light.

Can we make an electric fence with no physical wire?

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Can we make an electric fence with no physical wire? — AW, Karachi, Pakistan

No. An electric fence needs at least one real wire. When you put a large electric charge on this wire, anyone who touches it and the ground at the same time will serve as the path through which that charge will flow into the ground. They will receive a shock. But without either the charged wire or the ground, they won’t carry any electric current and they won’t receive a shock.

What is induced polarization and what are its applications?

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What is induced polarization and what are its applications? — PSD, Rio de Janeiro, Brazil

An electrically neutral object contains both positive and negative electric charges, however, those opposite charges are equal in amount and therefore cancel one another. But this cancellation doesn’t mean that the charges are unaffected by another nearby charge. If you hold an electrically neutral object near an electrically charged object, the charged object will cause a slight rearrangement of the charges in the neutral object. Charges opposite to that of the charged object will shift toward that object while charges like that of the charged object will shift away from that object. The neutral object will acquire an “induced polarization”, meaning that it its positive and negative charges are displaced relative to one another and that this displacement is “induced” by the presence of nearby charge. Induced polarization is a common effect and is present whenever lightning is about to strike the ground. As an electrically charged cloud drifts overhead, the objects on the ground acquire induced polarization. Their tops become covered with charge opposite that of the cloud and a lightning strike may occur between the cloud and the oppositely charged top of a tree or building.

What makes a paper airplane fly when its wings are not shaped like real airplane…

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What makes a paper airplane fly when its wings are not shaped like real airplane wings? — JC, Idaho Falls, ID

Even though a paper airplane’s wings are flat, they experience all of the aerodynamic forces found in more sophisticated wings. For example, when the air flowing past the paper airplane encounters the lower surfaces of its wings, this air slows down and its pressure rises above atmospheric pressure. However, while the air flowing over a sophisticated airplane wing experiences a substantial increase in speed and consequently a drop in pressure, this effect is very small in a paper airplane’s wing. Depending on how the air flows over or around the wing’s leading edge and whether or not it breaks away from the wing’s upper surface, the air pressure above the wing will be at or slightly below atmospheric pressure. Nonetheless, the air pressure below the wing is always slightly higher than that above the wing and the wing experiences a net upward aerodynamic force—a lift force. If you examine the airflow around a well-designed paper airplane wing, all of the flow features that occur around a sophisticated wing will be present but weak. Bowing the wing outward, as is done in a sophisticated wing, simply enhances those features so that the wing can lift a larger load.

Einstein’s famous equation E=mc2 says that mass is directly proportio…

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Einstein’s famous equation E=mc2 says that mass is directly proportional to energy. Does this mean that an object that is suspended overhead has more mass than an object located at ground level? — ST, Denver, CO

Yes, the mass/energy of a suspended object is greater than the mass/energy of that same object at ground level. The extreme example of this result comes with lowering an object slowly toward the surface of a black hole—as the object descends, its mass/energy diminishes until it reaches zero at the surface of the black hole.

What is a vacuum? Is it filled with charges with no mass?

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What is a vacuum? Is it filled with charges with no mass? — AW, Karachi, Pakistan

In principle, a vacuum is a region of space containing no real particles (no atoms, molecules, electrons, or other subatomic particles). Because the universe is filled with particles that pass easily through lots of matter (neutrinos, for example), it’s very hard to obtain a true vacuum. But let’s suppose that you could actually obtain a region of space with no real particles in it. That region of space would still contain large numbers of virtual particles at any given moment. These virtual particles are temporary quantum fluctuations of the vacuum; brief excursions of the quantum fields associate with various subatomic particles. These excursions are permitted by the Heisenberg uncertainty principle, which allows temporary violations of the conservation of mass/energy as long as those violations are extremely brief. While the presence of these virtual particles can only be detected indirectly, they are not massless. Except for their short lifetimes, these particles have characteristics similar to those of normal particles. In fact, if enough energy is used in the process of looking for a virtual particle, that virtual particle can be converted from virtual to real so that it can be detected directly. The energy of detection serves to “pay” for the mass of the particle so that it can leave the virtual realm and become a real, permanent particle.

Can one’s health be adversely affected by the use of certain wraps, films, or co…

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Can one’s health be adversely affected by the use of certain wraps, films, or containers, when heating food in the microwave?

When various plastics become hot, their molecules become more mobile. The most obvious such case is when a plastic actually melts. But even before it melts, a plastic can begin to lose molecules to objects that are touching it. However, the plastics used in cooking are pretty non-toxic, so that even eating pieces of those plastic won’t cause you any significant trouble. On the other hand, I would be careful with plastics that weren’t intended for cooking. Some non-food related plastics are mixed with additives called “plasticizers” that keep them softer than they would be if they were pure. These plasticizers have a tendency to migrate out of the plastics, giving such things as “vinyl” their characteristic odors. Heating a plastic containing a plasticizer can drive this plasticizer out of the plastic and into something else. I don’t think that it’s a good idea to eat plasticizers so I would suggest not cooking with plastics that weren’t intended for use with food. Still, not all plasticizers are bad—water is an excellent plasticizer for such common plastics as hair and cotton.

What are the key components of a microwave oven?

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What are the key components of a microwave oven?

In addition to the digital controller that runs the microwave, it contains (1) a power relay that allows the controller to turn on and off the microwave source, (2) a power transformer that produces the high voltage electricity needed by the magnetron, (3) a power rectifier that converts the alternating current from the transformer into the direct current needed by the magnetron, (4) a capacitor that smoothes out ripples in the direct current leaving the rectifier, (5) a magnetron that uses the high voltage direct current to produce an intense beam of microwaves, (6) a wave guide that transports the microwaves from the magnetron to the cooking chamber, and (7) a cooking chamber in which the food absorbs the microwaves and becomes hotter.