Author: Lou Bloomfield

If air in a rigid 80 cubic foot scuba tank is pressurized to 3000 psi, giving th…

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If air in a rigid 80 cubic foot scuba tank is pressurized to 3000 psi, giving the diver a certain amount of breathing time, then why does bottom time decrease with depth? I know about external pressure, but how does the pressure affect air inside the tank? – RJ

The deeper a scuba diver goes, the greater the water pressure and the more the water presses in on the diver’s chest. To be able to breathe, the air in the diver’s mouth must have roughly the same pressure as the water around the diver’s chest. That way, the diver will be able to use chest muscles to breathe the air into the diver’s lungs. But the pressure of the air in the diver’s mouth is proportional to its density and thus to the number of air molecules contained in each liter of air. At great depths, the diver must breathe dense, high-pressure air and this air contains a great many air molecules per liter. Since the scuba tank contains only so many air molecules, these molecules are consumed more rapidly at great depths than they are at shallow depths. The scuba regulator automatically controls the density of air entering the diver’s mouth so that the air pressure is equal to the surrounding water pressure. That way, the air is easy to breathe. The deeper the diver goes, the more air molecules the regulator releases into each of the diver’s breaths and the faster the air in the scuba tank is consumed.

Is heating milk by microwave advisable? – I

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Is heating milk by microwave advisable? – I

Microwave cooking leaves no permanent mark on the food. It causes virtually no chemical damage and absolutely no radioactivity. The only drawback with heating milk by microwave is that the heating may be uneven and may denature some protein molecules in regions of the milk that become excessively hot. Since most protein molecules are disassembled by your digestion anyway, this treatment probably has no effects worth worrying about. Even with infant formula, my only concern would be the hot spots. If you carefully shake the milk after heating, so that its temperature is uniform, it should be just fine. I suspect that companies warn you not to heat milk in a microwave because they are worried that you will either not shake the milk to distribute its temperature evenly or that you will overcook it until it boils and the bottle explodes.

How do the 2″ diagonal color LCD screens used in some of the new digital video …

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How do the 2″ diagonal color LCD screens used in some of the new digital video cameras work? — M, Waynesboro, MS

Like most liquid crystal displays (LCD), these devices use liquid crystals to alter the polarization of light and determine how much of that light will emerge from each point on the display. Liquid crystals are large molecules that orient themselves spontaneously within a liquid—much the way toothpicks tend to orient themselves parallel to one another when you pour them into box. The liquid crystals used in an LCD display are sensitive to electric fields so that their orientations and their optical properties can be affected electronically. The liquid crystals in the display occupy a thin layer between transparent electrodes and two polarizing plastic sheets. Light from a fluorescent lamp passes through a polarizing sheet, an electrode, the liquid crystal layer, another electrode, and another polarizing sheet. The orientation of the liquid crystal determines whether light from the first polarizing sheet will be able to pass through the second polarizing sheet. When electric charges are placed on the two electrodes, the liquid crystal’s orientation changes and so does light’s ability to pass through the pair of polarizing sheets.

To create a full color image, the display has many rows of electrodes on each side of the liquid crystals and a pattern of colored filters added to the sandwich. In “active” displays, there are also thin-film transistors that aid in the placement of charges on the electrodes. Overall, the display is able to select the electric charges on each side of every spot or “pixel” on the screen and can thus control the brightness of every pixel.

What would things look like if I could see wavelengths of the spectrum other tha…

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What would things look like if I could see wavelengths of the spectrum other than just visible light (e.g., X-rays, radio waves, ultraviolet, infrared, gamma rays, etc.)? — SH, Hurricane, UT

As you looked around, you would see a general glow of radio waves, microwaves, and infrared light coming from every surface. That’s because objects near room temperature emit thermal energy as these long-wavelength forms of light. While we don’t normally see such thermal radiation unless an object is hot enough for some of it to be in the visible range, your new vision would allow you to see everything glow. The warmer an object is, the brighter its emission and the shorter the wavelengths of that emission. People would glow particularly brightly because of their warm skin.

You would also see special sources of radio waves, microwaves, and infrared light. Radio antennas, cellular telephones, and microwave communication dishes would be dazzlingly bright and infrared remote controls would light up when you pressed their buttons.

You would see ultraviolet light in sunlight and from the black lights in dance halls. But there wouldn’t be much other ultraviolet light around to see, particularly indoors. X-rays and gamma rays would be rare and you might only see them if you walked into a hospital or a dentist’s office. Gamma rays would be even rarer, visible mostly in hospitals.

Why do colors fade in the sun? – RD

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Why do colors fade in the sun? – RD

While light travels as electromagnetic waves, it’s emitted and absorbed as particles called “photons.” Each photon carries with it a tiny bit of energy. The amount of energy in a photon depends on the wavelength of the light associated with it. While a photon of red light contains too little energy to cause chemical processes to occur in most molecules, a particle of violet or ultraviolet light contains enough energy to cause significant chemical damage to a typical molecule. Since sunlight contains a substantial amount of violet and ultraviolet lights, it can cause a fair amount of chemistry to occur in the molecules that absorb it. That’s why colors often fade in sunlight. Many colored molecules are relatively fragile and are damaged by photons of ultraviolet light. The portion of a dye molecule that gives it its color is called a “chromophore” and is usually the most fragile part of the molecule. Destroying its chromophore will often leave a dye molecule colorless. Exposure to sunlight was the traditional way to bleach fabrics and make them white.

How do flashing lights, chasing lights, and any type of Christmas lights work? -…

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How do flashing lights, chasing lights, and any type of Christmas lights work? – N

Years ago, many strings of Christmas lights consisted of about 20 or 30 light bulbs in series. In this series, electric current passed from one bulb to the next and deposited a small fraction of its energy in each bulb. The result was that each bulb glowed brightly so long as every bulb was working. If a single bulb burned out, the entire string went dark because no current could flow through the open circuit. If you replaced one of the bulbs in a working string with a special blinker bulb, the whole string would blink. The blinker bulb contained a tiny bimetallic switch thermostat that turned it off whenever the temperature rose above a certain point. At first, the bulb would glow and the whole string would glow with it. Then the thermostat would overheat and turn the bulb and string off. Then the thermostat would cool off enough to turn the bulb and string back on. This pattern would repeat endlessly.

But modern electronics has replaced the blinker bulbs with computers and transistor switches. Transistorized switches determine which bulbs or groups of bulbs receive current and glow at any given time and carefully timed switching can make patterns of light that appear to move or “chase.” As for the problem with one failed bulb spoiling the string, a reader has informed me that the bulbs are now designed with a fail-safe feature. If a bulb’s filament breaks, the sudden surge in voltage across that bulb activates this fail-safe mechanism. Wires inside the bulb connect to allow current to bypass that bulb completely. The remaining bulbs in the string glow a little more brightly than normal and their lives are shortened slightly as a result.

Radioactive elements’ half-lives are fixed and they decay at a constant rate. Th…

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Radioactive elements’ half-lives are fixed and they decay at a constant rate. Their decay rates have been determined thanks in part to our nuclear weapons research. Under what circumstances can a radioactive element have its decay rate changed? Can the element’s radioactivity be destroyed (cancelled) by applying high temperatures? If so, how high would the temperature have to go to achieve this? — RD, Humble, TX

Since radioactivity is a feature of atomic nuclei, the only way to alter radioactivity is to alter atomic nuclei. But there aren’t many ways to change atomic nuclei. Of various atomic and subatomic particles, only a neutron can enter a nucleus easily and cause it to rearrange. However, it’s more common for a neutron to increase radioactivity than to destroy it, so that’s not a good approach. Furthermore, the only practical way to obtain neutrons is with radioactivity.

Heating a collection of nuclei can cause them to collide and rearrange. However, this process is also fraught with problems. The products of the fusion and fission events that occur when nuclei collide will probably be radioactive themselves, so that it’s unlikely that heating radioactive materials will make them less radioactive. Instead, it’s likely that heating radioactive materials will make them more radioactive. Furthermore, the temperatures at which nuclei will begin to collide are extraordinarily high. Even the smallest nuclei repel one another fiercely so that they need temperatures of 100 million degrees C or more to begin colliding effectively. Larger nuclei, such as those common in nuclear wastes, won’t collide until their temperatures exceed 1 billion degrees C. The only way to reach these temperatures is with nuclear weapons and they certainly don’t reduce the radioactivity of nearby materials. In short, the only way to get rid of radioactivity is by waiting patiently.

Can you explain how the telephone wiring in my home works for the telephone? My …

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Can you explain how the telephone wiring in my home works for the telephone? My touch-tone phone has 4 wires, but I understand that only 2 wires are used. Does the phone use the other 2 wires for the light on the phone pad, etc.? — DS, Larkspur, CA

Your telephone performs all of its functions using only those 2 wires. The 2 extra wires are virtually never used by a single-line telephone. The only exception that I’m aware of is the old “Princess Telephone,” which had a special light powered by the extra pair of wires. In most telephones, even the power for the lighted keys comes from the 2 main wires. While the telephone is off the hook, the telephone company sends a constant DC current through those two wires. This current powers the telephone’s electronics and its lights. When you talk, the microphone causes the telephone’s electric impedance to fluctuate up and down and this variation causes sound to be reproduced in your friend’s earpiece. Pressing the dialing buttons causes similar fluctuations in impedance and the telephone company uses these tones to make the proper connections. When the telephone company rings your telephone, they send a higher voltage AC current through the two wires and the telephone’s bell rings.

How does an infrared sensor faucet work?

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How does an infrared sensor faucet work? — DD, Sacramento, CA

The sensor has two lenses: one that emits a beam of infrared light and the other that looks for a reflection of that light. As long as there is nothing beneath the faucet, there is very little infrared light reflected back toward the sensor and the sensor prevents any water from flowing out of the faucet. But when you hold your hands under the faucet, the infrared light reflects from your hands and some of it returns to the sensor. The sensor detects this light and opens an electronic valve to permit water to flow out of the faucet. The lenses are aimed so that only objects under the faucet itself will reflect the infrared light back toward the lens. A more distance object may reflect some of the infrared light, but the light won’t pass through the sensor at the proper angle and won’t be detected.

How fast is the earth moving through space? Does this movement affect our percep…

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How fast is the earth moving through space? Does this movement affect our perception of time? — GR, Grabil, IN

Because there is no preferred reference frame for the universe, we can only talk about the earth’s speed in reference to other objects. For example, the earth is moving at about 5 kilometers per second relative to the sun and about 30,000 kilometers per second relative to the center of the galaxy. These speeds do affect our perceptions of time, so that times passes at a different rate for us than for someone closer to the sun or to the galactic center. However, gravitational wells also affect the perception of time, so that the effects are complicated. The earth is also receding extremely rapidly from objects at the far side of the universe; so fast that time passage is dramatically affected. Those distant objects appear to be aging very slowly and their light is shifted substantially toward the red.