Author: Lou Bloomfield

Is there any easy way to mold plastics?

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Is there any easy way to mold plastics?

The easiest way to mold plastics is to form them directly inside a mold. Most plastics are made by attaching small molecules to one another in a process called polymerization. You begin with one or more small molecules or “monomers” and cause them to link together into in a “polymer.” You can initiate this polymerization with chemical catalysts, light, or even heat. There are many plastic-forming systems that you can buy commercially. You simply mix a few chemicals together, pour the mixture into a mold and wait. Once the polymerization has finished, you have a molded piece of plastic.

If you don’t want to do the polymerization yourself, you can start with a finished plastic and melt it. Most plastics that haven’t been vulcanized into one giant molecule (as is done in rubber tires) will melt at high enough temperatures (although some burn or decompose before they melt). These molten plastics can be stretched, squeezed, or poured into molds to make just about any shape you like.

How does an ear thermometer work so quickly?

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How does an ear thermometer work so quickly? — SN, West Covina, California

An ear thermometer examines the spectrum of thermal radiation emitted by the inner surfaces of a person’s ear. All objects emit thermal electromagnetic radiation and that radiation is characteristic of their temperatures—the hotter an object is, the brighter its thermal radiation and the more that radiation shifts toward shorter wavelengths. The thermal radiation from a person’s ear is in the invisible infrared portion of the light spectrum, which is why you can’t see people glowing. But the ear thermometer can see this infrared light and it uses the light to determine the ear’s temperature. The thermometer’s thermal radiation sensor is very fast, which accounts for the speed of the measurement.

What are the relative efficiencies of the fission and fusion reactions in thermo…

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What are the relative efficiencies of the fission and fusion reactions in thermonuclear weapons? Is every last grain of fissile and fusible matter converted to energy or is there a loss somewhere?

While both fission and fusion convert substantial fractions of the mass in a thermonuclear weapon into energy, most of the bomb’s initial matter remains matter, not energy. When a uranium nucleus fissions to become smaller nuclei, about 0.1% of the uranium nucleus’s mass becomes energy. When two deuterium nuclei—the heavy isotope of hydrogen—fuse together to become helium, about 0.3% of the deuterium nuclei’s masses become energy. Despite these seemingly small percentages, this scale of matter to energy conversion dwarfs that of chemical explosives, which convert only parts per billion of their masses into energy.

While fusion is somewhat more energy efficient than fission, that’s not the whole reason why hydrogen bombs (thermonuclear bombs) are more powerful than uranium bombs (fission bombs). The main reason is that thermonuclear bombs can be much larger than fission bombs because there is no upper limit to the amount of hydrogen you can assemble in a small region of space. In contrast, if you assemble too much fissile uranium in a small region of space, a chain reaction will begin and the material will overheat and explode. At the height of the cold war, the Soviet Union built gigantic thermonuclear weapons with explosive yields as large as 100 megatons of TNT.

How does a parabolic microphone work?

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How does a parabolic microphone work? — KL, Regina, Saskatchewan

A parabolic microphone is effectively a mirror telescope for sound. When sound waves strike the dense, rigid surface of the parabolic dish, they partially reflect. This reflection occurs because sound travels much faster in a rigid solid than in the air and changes in the speed of a wave cause part of it to reflect. In this case, the reflection redirects the sound waves inward because the reflecting surface is curved and the sound waves form a real image of the distant source that produced them. While you can’t see this real image with your eyes, you can hear it with your ears. If you were to mount a large parabolic dish so that it faced horizontally and then moved your ear around in the focal plane of the dish, you would hear sounds coming from various objects far away from the dish. The same effect occurs for light when it bounces off a curved mirror—a real mirror telescope. A TV satellite dish is the same thing, but this time for microwaves! In all three cases, the real images that form are upside down. To make a parabolic microphone, you normally put a conventional microphone in the central focus of a parabolic surface so that the microphone receives all the sound coming from objects directly in front of the parabola. To listen to different objects, you simply steer the parabola from one to the other. This is exactly what a TV satellite dish does when it wants to “listen” to a different satellite—it steers from one to the other.

Why do you hear different music coming from a compact disc when the laser of the…

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Why do you hear different music coming from a compact disc when the laser of the CD player is just going around the same part of the CD over and over again? — KD, McMinnville, OR

The CD player’s laser doesn’t really go over the same part of the CD over and over again. As the disc turns, the laser slowly moves outward from the middle of the disc toward its edge. The laser beam is focused to an extremely small spot inside the disc and it is carefully following a tight spiral ridge in the aluminum layer inside. This ridge runs continuously from the center of the disc to its edge. With each revolution of the disc, the laser works its way outward by one more turn of the spiral. The ridge has interruptions in it every so often and it is this pattern of interruptions that contains the information needed to reproduce sound.

If you were out in space and could see every individual person clearly, would it…

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If you were out in space and could see every individual person clearly, would it look like they were walking at a slant? — KD, McMinnville, OR

To the astronauts orbiting the earth, up and down have very little meaning. Because they are falling all the time, these astronauts have no feeling of weight and can’t tell up from down without looking. If an astronaut were to look at a person walking on the ground below, that person might easily appear at a strange angle, depending on the astronaut’s orientation and point of view.

I heard on a news report that there is a paint that will generate heat from a 12…

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I heard on a news report that there is a paint that will generate heat from a 12-volt battery. What can you tell me about this subject? — JF

Generating heat from a battery is relatively easy. All you need is a material that conducts electricity only moderately well and you’re in business. If you allow current to flow through that material from the battery’s positive terminal to its negative terminal, the current will lose energy as it struggles to get through the material and the current’s lost energy will become thermal energy in the material. The only difficult part of this task is in choosing the right material so that it doesn’t produce too much or too little heat. In short, the electric resistance of the finished material has to be in the right range. For a solid system that you can cut and tailor, that’s not much of a problem. But for a paint, it could be tricky. To make an inexpensive paint, it would probably need to use carbon powder as the electric conductor. A thin layer of carbon granules held in place by a plastic of some sort would probably provide a suitable conducting surface that would become warm when you allowed current to flow through it from a battery. There are copper and silver conducting paints that might also work, but these are rather expensive and I’m not sure how they behave at elevated temperatures.

I heard of a laser induced fluorescence instrument that is used in aiding cancer…

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I heard of a laser induced fluorescence instrument that is used in aiding cancer diagnosis. Could you tell me how this instrument works?

You are probably referring to a device developed at the BC Cancer Research Center in Vancouver, British Columbia and now available commercially from Xillix Technologies. A scientist from that research center gave me the following description of their technique.

The instrument is based on the discovery that most tissues when illuminated by blue or UV light emit a natural fluorescence spectral signature known as autofluorescence. This fluorescence signature is the sum of the emission of the various biochemical fluorphores present in the tissue. If the tissue chemical or physical structure changes, then the spectral signature changes. By exploiting differences in the spectral signature between cancerous and healthy tissue one can create an imaging device that can “see” the difference in the color of the autofluorescence of the tissue and detect changes that may indicate the presence of cancer. The sensors used to see the low levels of fluorescence light employ similar technology to military night vision devices. Once areas of change are located and confirmed by analysis of a biopsy sample treatment can begin. This technique is primarily useful for early stage cancers that are not visually apparent to a physician.

How can I build an AM radio?

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How can I build an AM radio?

That’s a very open ended question so I’ll describe the simplest AM radio I can think of—a crystal radio. A crystal radio already addresses most of the issues of AM radio and more sophisticated AM radios just improve on its performance.

You need only four basic components for a crystal radio: an antenna, a tank circuit, a diode, and a high-impedance earphone.

The antenna is a long wire that projects upward into the electromagnetic fields of the passing radio wave so that electric charges begin to move up and down its length. The ideal length for this wire is a quarter of the wavelength of the wave you’re trying to receive, but since that’s hundreds of meters for a typical AM station, you’ll have to settle for a shorter than ideal antenna.

The tank circuit is a coil of wire that’s connected at each end to the two ends of a capacitor. In a typical crystal radio, one of these items—either the coil or the capacitor—is adjustable and forms the tuning element that allows you to select a particular AM station. The tank circuit is a resonant device—electric charges and current flow back and forth through it rhythmically at a specific frequency. If that resonant frequency is adjusted so that it coincides with the transmission frequency of an AM radio station, the small currents flowing in the antenna that’s connected to the tank circuit will excite large movements of charge and current in the tank circuit.

The diode is also connected to the tank circuit. Its job is to extract some of the charge that oscillates back and forth in the tank circuit and to send that charge to the earphone. By allowing current to flow only in one direction, the diode samples the overall amount of charge moving in the tank circuit. What it passes to the earphone is a measure of how strong the radio wave is, which is actually the form in which the AM radio station is transmitting sound information.

The high-impedance earphone uses the diode’s tiny charge deliveries to reproduce sound. The diaphragm inside the earphone moves back and forth as the amount of charge passing through the diode fluctuates up and down. Each time the radio wave increases in strength, the diaphragm moves in one direction. Each time the radio wave decreases in strength, the diaphragm moves in the other direction. Thus as the radio station varies the strength of its radio wave, the earphone’s diaphragm moves back and forth and it reproduces the sound.

Does a device that has radio waves and uses ozone and negative ions have the abi…

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Does a device that has radio waves and uses ozone and negative ions have the ability to clean the air in my home? — KTR, Halifax, Nova Scotia

There are many simple electronic devices that claim to clean the air in your home by making negative ions and ozone (if they involve any radio waves, it’s a minor side effect of their internal electronics). The claim is accurate—they do make both ozone and negative ions, and they do clean the air in your home. However, that’s not the whole story. First, ozone may have the “fresh” smell that occurs after a thunderstorm (a potent producer of ozone), but ozone is a powerful oxidizing agent and chemical irritant that’s considered an environmental pollutant rather than a charming scent. The manufacturers are taking a nuisance effect and touting it as a “valuable feature.” Second, the negative charges emitted by these electronic devices attach themselves to dust, ash, pollen, and smoke particles and cause those particles to bind themselves to your walls and furniture. The air really does become cleaner, but every surface in your home becomes dirtier as a result.

If you’re seriously interested in cleaning the air in your home, you are probably better off with a full electrostatic air cleaner. Small home versions of this common industrial workhorse are easy to obtain at a local heating and air conditioning store. Properly designed machines use positive ions to avoid producing ozone and provide a negatively charged surface for the positively charged dirt to stick to so that it doesn’t deposit itself on your walls.