Author: Lou Bloomfield

How does a TV or VCR remote control work? Is it infrared light or a laser? How d…

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How does a TV or VCR remote control work? Is it infrared light or a laser? How does the TV or VCR know what to do with the light it receives from the remote? — FC, Lafayette, CA

The remote unit communicates with the TV or VCR via infrared light, which it produces with one or more light emitting diodes (LED). The most remarkable feature of this communication is that the TV or VCR is able to distinguish the tiny amount of light emitted by the LED from all the background light in the room. This selectivity is made possible by blinking the LED rapidly at one of two different frequencies. Since it’s unlikely that any other source of light in the room will blink several hundred thousand times per second and at just the right frequency, the TV or VCR can tell that it’s observing light from the remote. The remote sends information to the TV or VCR by switching back and forth between the two different frequencies. For example, it may use the higher frequency to send a “1” bit and the lower frequency to send a “0” bit. The remote sends a long string of these 1’s and 0’s, and the TV or VCR detects and analyzes this string of bits to determine (1) whether it’s directed toward the TV or VCR (an address component in the information) and (2) what it should do as the result of this transmission (a data component in the information). Assuming that the string of bits was intended for the TV or VCR, its digital controller (a simple computer) takes whatever action the data component of the transmission requested.

How dangerous is the radiation from high voltage power lines? – K

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How dangerous is the radiation from high voltage power lines? – K

Probably not very dangerous. The radiation itself is so weak that it can’t cause significant heating in your body (as the microwaves used in diathermy treatment do) and so low frequency that it can’t do chemical damage (as the X-rays from a CT scan do). The only possible source of trouble is the small electric and magnetic fields from the power lines and there is still no credible evidence that these affect biological tissue. Moreover, there are sound physical arguments why those fields should not be able to affect biological tissue. Only in rare cases of an organ that is devoted to sensing magnetic fields (e.g., in migratory birds) is there any reasonable interaction between tissue and small magnetic fields.

Is it true that Tesla invented a way to send electrical power without the use of…

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Is it true that Tesla invented a way to send electrical power without the use of power lines? If so, how? – BS

Yes. Tesla found that the alternating electromagnetic fields around a large high frequency transformer could propel currents through wires or lamps that were located at a moderate distance from the transformer. But this technique of using the alternating fields near a transformer to provide power aren’t very practical—there is too much power wasted through radiation or in heating things that aren’t meant to be heated.

What is white noise? – AT

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What is white noise? – AT

Acoustic “white noise” is a collection of random sounds that together have the same volume at every frequency or pitch. It’s defined more accurately as having the same amount of power in each unit of its bandwidth, so that the acoustic power between 20 and 21 cycles per second is the same as the acoustic power between 500 and 501 cycles per second.

What happens to water in space?

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What happens to water in space? — DZ, Illinois

That depends on the water’s temperature. At extremely low temperatures, ice remains stable indefinitely. That’s why comets that are as old as the solar system have been able to hold on to their water despite having almost no gravity. But at more moderate temperatures, ice and water both slowly lose water molecules. These water molecules evaporate (or sublime, in the case of ice) and drift off into space. Because there’s no air pressure in space to prevent evaporation from occurring inside the body of water, water will actually boil at any temperature. That’s what boiling is: evaporation into steam bubbles located inside the water. Atmospheric pressure normally smashes these bubbles as long as the water temperature is below 212° F (100° C), but in empty space the bubbles form without opposition at any temperature.

When ice placed in water melts, does the overall volume of water increase, stay …

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When ice placed in water melts, does the overall volume of water increase, stay the same, or decrease? — AB, Riverside, CA

The volume decreases. That’s because ice at 32° F (0° C) is less dense than water at that same temperature. As the ice melts to form water, the density of its molecules increases and the overall volume of material decreases. This situation, in which the solid form of a material is less dense than the liquid form of that material, is virtually unique in nature and explains why ice floats on water.

What is an electron and what keeps its mass and charge together so that when the…

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What is an electron and what keeps its mass and charge together so that when the mass moves, the charge moves with it? — WG, Calgary, Canada

An electron is a fundamental particle that has as two of its attributes, a mass and an electric charge. Because the electron appears to be structureless, it has no size and it wouldn’t make sense for its mass to be located at a distance from its charge. With a less fundamental particle such as a proton, the charge and mass can be somewhat spread out and displaced so that the charge and mass can move slightly independently. Still, even in the case of a proton there are effects that keep the mass from getting far away from the charge.

How does electricity travel through wires?

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How does electricity travel through wires?

When the atoms that make up a metal assemble together, some of their electrons become delocalized—they stop associating with specific atoms and can move throughout the overall metal. Most importantly, these mobile electrons can respond to the presence of electric fields and electric forces by accelerating and traveling through the metal. When you turn on a flashlight, you are creating a system in which positive charges on one terminal of the battery and negative charges on the other terminal can begin to push electrons through the flashlight’s wires. The mobile electrons in those wires are negatively charged and they accelerate toward the positive terminal of the battery. New electrons from the negative terminal of the battery replace the departing electrons and soon a steady flow of electrons through the flashlight is established.

How do scientists measure the speed of light?

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How do scientists measure the speed of light? — DZ, Illinois

There are many possible methods for measuring the speed of light, but the classic technique is easiest to describe. In this method, a rapidly spinning mirror is used to direct a beam of light down a long pipe toward a stationary mirror at the end of that pipe. The first mirror is spinning in such a way that the beam it reflects sweeps across the pipe and can only strike the second mirror during that brief moment when the first mirror is perfectly aligned to direct the light down the pipe. A scientist then looks into the spinning mirror to observe the flash of light that returns from the second mirror. Because it takes a small but finite amount of time for the light to travel back and forth through the pipe, the spinning mirror will have turned a little between the moment when it sent the beam of light toward the far mirror and the moment when that beam of light returns to the spinning mirror. By studying the angle at which the reflected beam leaves the spinning mirror and by knowing how quickly the mirror is spinning, the scientist can determine the speed of light.

However, something has changed since those sorts of measurements were done: the speed of light is now a defined constant. It isn’t measured any more—it’s simply defined to be 299,792,458 meters per second. The second is defined in a similar manner—as 9,192,631,770 periods of a particular microwave emission from the cesium-133 atom. Because of these two definitions, an experiment that “measures the speed of light” is now used to determine the length of the meter.

I have seen some new 48″ fluorescent tubes rated at 25W compared to the standar…

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I have seen some new 48″ fluorescent tubes rated at 25W compared to the standard 40W. I was told I could use these in my existing fixtures without doing anything to the ballast. What effect will replacing a 40W bulb with these 25W bulbs have on my fixtures and ballasts? – ST

I would guess that the lower wattage tubes will work fine in your existing fixtures, but I am not expert enough to be certain. The 25W tube itself is evidently built so that a smaller current flows through it than through a normal 40W tubes when the two are exposed to similar voltages. The ballast’s job is to prevent a catastrophic rise in that current by adjusting the voltage across the tube dynamically during each half cycle of the power line and to keep the tube operating even as a half cycle is coming to an end. Although the 25W tube will draw less current than the ballast expects, the ballast should behave pretty well. I would expect that the tube designers have anticipated this situation and have built the tube to operate with the standard ballast. If a reader knows better, please let me know.