Author: Lou Bloomfield

How much water power do you need to turn on a light bulb? How much wind power do…

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How much water power do you need to turn on a light bulb? How much wind power does it take to turn on a light bulb? Can artificial light make a solar paneled car run? If so, how bright? — BB, Stafford Springs, CT

If you are trying to light a 60 watt bulb, you must deliver 60 watts of electric power to it (unless you are willing to have it glow relatively dimly). So the answers to your questions are 60 watts of waterpower and 60 watts of windpower. But you are probably more interested in how much water or wind is needed to run those power sources. An efficient water generator that produces 60 watts of power lowers about 6 liters (or one and a half gallons) of water about 1 meter (or 3 feet) each second. An efficient wind generator that produces 60 watts of power stops about 1 cubic meter (or 32 cubic feet) of air moving at 36 km/h (or 21 mph) each second. Finally, a solar powered vehicle needs at least several hundred watts of power to operate. Since solar panels are only about 20% energy efficient and artificial light sources are also only about 10 to 50% energy efficient, it would take thousands of watts of artificial lighting to operate a solar powered car. Not very practical.

I have to do an experiment for school on the electromagnetic properties of iron,…

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I have to do an experiment for school on the electromagnetic properties of iron, steel, and aluminum. The only problem is that I am not too sure what I should be testing. Any ideas? — CP, Nassau, Bahamas

Iron and steel (not stainless) are ferromagnetic metals, meaning that they are intrinsically magnetic. While this magnetism is normally hidden by the formation of millions of tiny, randomly oriented magnetic domains, it becomes apparent when you hold a magnet near the iron or steel: they are attracted! Aluminum has no intrinsic magnetism and is not attracted to a magnet. There are far more non-magnetic metals than magnetic ones. Why don’t you try to see which metals will stick to a magnet. Only the ferromagnetic ones will. Even common stainless steel is non-ferromagnetic.

How do stalactites and stalagmites form in caves?

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How do stalactites and stalagmites form in caves? — GS, Conroe, TX

They form when various minerals come out of solution in water and crystallize on the surfaces of a cave. To understand how this process occurs, we must look at the interface between the water and the cave surface. Whenever water is in contact with a mineral surface, there is a chance that an atom of the surface will suddenly leave the surface and dissolve in the water. If there are atoms already dissolved in the water, there is also a chance that one of them will suddenly come out of solution in the water and attach to the surface. Atoms leave and return to cave surfaces all the time as water drips from the ceiling of a cave to its floor.

What is important for the growth of stalactites and stalagmites is that more atoms stick to the cave surfaces than leave those surfaces. That is exactly what happens and it does so because the water has already picked up more than enough dissolved atoms before it reaches the stalactite. Either because of temperature changes or because of evaporation, the water that runs across the cave roof and down the sides of a stalactite deposits more atoms on the stalactite’s surface than it removes. The same goes for the stalagmite after the water drips down to the cave floor. As the atoms build up on the cave surfaces, the stalactites grow down and the stalagmites grow up.

At times a very thin invisible layer of ice forms on road surfaces. The road sur…

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At times a very thin invisible layer of ice forms on road surfaces. The road surface appears dry and does not have the telltale reflections of ice. Many people refer to this as “black ice.” How is this ice formed? What are the crystal properties that make it invisible? – BK

Black ice is a layer of ice that is almost free of internal defects or air bubbles and that does not have a smooth surface. The absence of internal defects or air bubbles is what makes it transparent rather than white. Snow and crushed ice appear white because they contain countless tiny surfaces. Whenever light changes speed, as it does in going from ice to air or air to ice, some of that light reflects. Since snow and crushed ice contain many ice/air interfaces, they reflect light extensively and appear white. In contrast, black ice contains no internal ice/air interfaces and doesn’t reflect any light from inside. Any light that makes it into the black ice goes all the way to the roadway. If the roadway reflects any of this light, it again passes unscathed through the black ice. The only evidence that the black ice exists at all comes from its surface, but here again the ice offers little that you can see. Since true black ice is microscopically rough, the small amount of light that reflects as it enters the ice from the air is reflected randomly in all directions. So little of that reflected light travels in any one direction that you can barely see it at all. Overall, black ice reflects so little light that you see only the roadway itself. While I am not sure, I think that it forms when moisture in the air condenses to dew on the roadway and then freezes into ice. Whatever process forms it must leave it almost without holes and therefore invisible.

What is analog? I hear about digital audio being better than analog, but nobody …

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What is analog? I hear about digital audio being better than analog, but nobody defines what analog is. — DG, Houston, TX

In analog audio, the air pressure fluctuations of sound at the microphone are represented by a continuously variable physical quantity such as an electric current, a voltage, or a magnetization. Thus as the air pressure at a tape recorder’s microphone rises during one moment of a song, an electric current in the recorder will rise and a region of a magnetic tape surface will become particularly strongly magnetized in a particular direction. Overall, each value of air pressure is converted to a particular value of the physical quantity.

The problem with analog recording is that when the sound is recreated, any defect in the physical quantity representing air pressure will lead to an imperfection in the reproduced sound. For example, if the magnetization of the recording tape has changed slightly due to how it was stored, the sound that the tape recorder produces won’t be exactly the same as the sound that the microphone heard. Digital recording avoids this problem by recording the information as bits. The physical quantity such as magnetization is representing bits (which take only two possible values) rather than the air pressure itself (which can take a broad range of values). Minor changes in the physical quantity representing these bits won’t change the bits. Thus imperfections in the recording or playback process won’t affect the sound quality.

How do fletchings stabilize an arrow in flight after it is shot from a bow?

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How do fletchings stabilize an arrow in flight after it is shot from a bow? — SH, Newton, TX

Like all isolated objects, the arrow naturally pivots about its own center of mass, a point located near its geometric center. If the arrow had no fletchings (or fins) it would tend to rotate wildly in flight. But the fletchings experience substantial aerodynamic forces whenever the arrow isn’t flying point first and these aerodynamic forces twist the arrow back toward its proper orientation. Thus whenever the arrow begins to rotate so that its point isn’t first, the air pushes hard on the fletchings and returns the arrow to its point-first orientation. The same effect keeps airplanes and birds flying nose (or beak) forward.

If I want to create a radio controlled device, how do I make sure it does not cr…

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If I want to create a radio controlled device, how do I make sure it does not create interference with other devices or receive interference. How does digital RF work and does it stop interference problems? — KG, New York, NY

Radio interference occurs whenever two nearby radio transmitters are simultaneously emitting radio waves that overlap in space and frequency. The receivers for these two waves can’t tell them apart and end up receiving both at once. This interference is familiar with AM radio, where you can sometime hear two broadcasts at the same time. With FM radio, the receivers are clever enough to distinguish one radio wave from another, but they can’t determine which broadcast they’re supposed to follow. Instead, they lock onto whichever wave is strongest and will often flip back and forth from one station to the other as their signal strengths fluctuate.

The only way to avoid interference completely is to choose a radio frequency that no one else nearby is using. That way your transmission is certain to be stronger than any other at the same frequency and your receiver will follow only your broadcast. If you have no choice but to share a particular frequency, then you must use some encoding scheme such as digital transmission so that your receiver can tell when it’s receiving a broadcast from your transmitter and not from some other transmitter. Your receiver looks for your personal encoding scheme and won’t respond to that of some other transmitter. However, if that other transmitter is strong enough, it will probably prevent your receiver from detecting your transmission. That trick of overwhelming a receiver with a second transmission is the principle behind jamming of a radio transmission.

How can I check the magnetron in a home microwave oven? I have checked the HV (h…

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How can I check the magnetron in a home microwave oven? I have checked the HV (high voltage) transformer, the rectifier, and capacitor and all are OK. Does the magnetron output decrease with age? The oven has a hum that is much louder than normal. — AA, Ontario, CA

While I have only a little experience repairing microwave ovens, I can make reasonable guesses. The loud hum you hear is probably an indication that something is overloading the power transformer. That suggests that the diode, capacitor, or magnetron are bad. If you have checked the first two carefully, at full operating voltage, and found no problems, then I would suspect the magnetron. I have been told by a reader that magnetrons usually fail by shorting out, the result of electromigration of the filament material. The tube would then draw excessive currents from the high voltage transformer. That has probably happened in your case. Still, free advice like mine is only worth what you’ve paid for it. I’d suggest you consult a local repairperson, who has test equipment that can pinpoint the problem in seconds.

When I read of scientists discovering galaxies “on the edge of the universe,” …

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When I read of scientists discovering galaxies “on the edge of the universe,” perhaps 15 billion light years away, I wonder if they are including the distance the objects must have traveled in the time it took for the light to reach their telescopes. Very distant objects are said to be receding from any other point in space at a higher rate than closer objects. If a galaxy is discovered 15 billion light years away today, the light left that galaxy 15 billion years ago while receding at a high rate. Where is it today, really? Twice as far away? — DK, Missouri City, TX

This seemingly simple question has a surprisingly complicated answer. You might expect that if the earth and one of these distant galaxies had been very near one another at the creation of the universe and had both been moving away from one another at almost the speed of light, that after 15 billion years each would have moved almost 15 billion light years in opposite directions and would thus be separated by almost 30 billion light years. That’s not the case. That simple view ignores the important effects of special relativity on rapidly moving objects.

To understand these effects, suppose that there was an observer who was stationary at the creation and watched the earth and galaxy head off in opposite directions at almost the speed of light. From that observer’s perspective, the two objects are heading away from one another at almost twice the speed of light. After 15 billion years, this observer sees the galaxy as almost 30 billion light years away from the earth.

Now suppose that there was another observer who was on the earth at the creation. From this person’s perspective, the galaxy recedes from the earth at almost the speed of light, but no more. Nothing can move faster than speed of light! After 15 billion years, this observer sees galaxy as almost 15 billion light years away from the earth.

These two observations don’t seem to agree. The problem lies in how the two observers perceive time and space. According to special relativity, observers who are moving relative to one another don’t perceive time and space in the same way. Their perceptions will be so different that they will not even agree about just when 15 billion years has passed.

With this long introduction, here is the answer to your question: no distant galaxy in the observable universe can ever be farther from us than the distance light has traveled since the creation of the universe. Since that creation was about 15 billion years ago, the most distant possible galaxy is almost 15 billion light years away.

How does a dishwasher machine work?

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How does a dishwasher machine work? — WW, Bochum, Germany

A dishwasher is really a number of simple machines that work together to clean dishes. These machines are controlled by a mechanical or electronic timer and include an electrically operated water valve, a water level sensor, one or two water pumps, a thermostat, an electric heating element, one or more rotating spray nozzles, and a fan.

The cycle begins when the timer sends electric current through a coil of wire in the water valve, making that coil magnetic and pulling the water valve into its open position. Water flows then flows from the high pressure in the water line to the atmospheric pressure in the cleaning chamber. When the water sensor detects that the dishwasher is adequately filled, it shuts off current to the valve and the valve closes.

The thermostat measures the water temperature and may delay the start of the cycle if the water is too cool. If so, it directs electric current through the heating element, where that current’s energy is converted into thermal energy and transferred to the water. When the water is hot enough, the cycle continues.

During the cleaning cycle, one or more pumps operate. They add energy to the water and increase its pressure. This high-pressure water flows slowly to the rotating nozzles and then accelerates to high speeds as it enters the narrow openings and sprays out into the low-pressure cleaning chamber. As the high-speed water collides with the dishes and slows down, its pressure rises again and begins to exert substantial forces on the food particles. The food particles are pushed off the dishes and fall into the bottom of the dishwasher. Soap added to the cleaning water forms tiny spherical objects called micelles that trap and carry away fats that would otherwise not mix with water. At the end of the cycle, the water, food particles, and fat-filled soap micelles are pumped down the drain.

The cleaning cycle may repeat with fresh water and is then followed by a rinse. A soap-like surfactant may be added to the rinse water to lower its surface tension and prevent it from beading up on the dishes. When the pumps have removed the last of the rinse water, a fan begins to blow air over the dishes. The heating element may heat this air to assist evaporation. The water molecules leave the surfaces of the dishes and become gaseous water vapor. The dishes are left clean and dry.