Author: Lou Bloomfield

How much life is consumed each time you turn on a fluorescent lamp?

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How much life is consumed each time you turn on a fluorescent lamp? — BL, San Jose, CA

The starting process erodes the electrodes of a fluorescent tube through a phenomenon called sputtering. A typical fluorescent tube will last about 50,000 hours if left on continuously but only 20,000 hours if it’s turn on for just 3 hours at a time. From that tidbit, I think its fair to say that a fluorescent tube can only start about 10,000 times. If the tube costs $5, you are spending about 0.005 cents per start. If the electricity to operate that tube costs about 0.2 cents per hour, then turning the tube off for about 1.5 minutes saves the same amount of money in electricity as it costs in tube life when you turn the tube back on. In short, if you turn the lamp off for less than about 1 minute, you’re wasting money. But if you turn it off for more than 10 minutes, you’re saving money. In between, it’s not so clear. There is a myth that turning on a fluorescent lamp consumes a huge amount of electricity so that you shouldn’t turn the lamp off and on. There is simply no basis to that myth.

How does a sewing machine work?

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How does a sewing machine work? — RD, APO

A sewing machine uses a spinning shaft to push a needle up and down through fabric. The rod that controls the needle’s height is attached to the spinning shaft away from the shaft’s axis of rotation so that as the shaft spins, the rod and needle move up and down. This motion resembles that of a child on a tricycle: as the front wheel turns, the child’s legs move up and down.

Thread from a spool held above the fabric passes through an eye in the needle’s tip, so that as the needle pierces the fabric, it carries the thread with it. A device beneath the fabric catches hold of this thread and pulls it rapidly around a smaller spool of thread (the bobbin). The thread from above the fabric thus fully encircles the thread from this bobbin and the two threads become permanently locked together. When the needle withdraws from the fabric, some of the thread that it carries remains behind, locked around the thread from the bobbin below. With each stroke of the needle, a new joint is created between the thread from above the fabric and the thread from below the fabric. If there are several pieces of fabric lying on top of one another, these pieces become locked together by the intertwined threads.

Can you get electricity or some sort of energy or power from fruit?

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Can you get electricity or some sort of energy or power from fruit? — J, Embrun, Ontario

The answer is yes, but the method may not be what you had in mind. While it’s possible to make a battery by inserting two dissimilar metal strips into the fruit, the battery that results is really powered by the metals themselves. The fruit juice just acts as an “electrolyte”—an electrically conductive liquid that facilitates the movement of electric charges. Claiming that the fruit is responsible for the energy is like claiming that the stone in “stone soup” (an old tale about a beggar who tricks the villagers in a community into contributing vegetables to spice up the soup that he’s making with his magic stone) is really the basis for the soup.

The best way to obtain energy from the fruit is to eat it! The sugars and starches in the fruit have plenty of chemical potential energy that’s released when those chemicals are oxidized in your body. This released energy is what allows you to live, work, and play.

How does an amplifier work and what are the basic components of one?

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How does an amplifier work and what are the basic components of one? — WT, Albuquerque, NM

A typical amplifier examines the current flowing in its input circuit and produces a current in its output circuit that’s proportional to but much larger than this input current. The factor by which the amplifier multiplies the input current to produce the output current is sometimes called the amplifier’s “current gain.” The tiny currents produced by a microphone attached to an audio amplifier’s input circuit are boosted into huge currents that flow through speakers attached to the amplifier’s output circuit. Since your voice is controlling these large currents, the speakers reproduce the sound of your voice.

While there are many techniques used to amplify currents, most modern audio amplifiers use transistors to do the amplification. A transistor is a device that permits a small current or electric charge to control the flow of a much larger current. The transistors inside the amplifier examine the current in the amplifier’s input circuit and these transistors control the current passing through the amplifier’s output circuit. Because the current in the output circuit needs electric power to continue flowing, a power supply inside the amplifier provides that current with power. As you talk into the microphone, the transistors adjust the current flowing through the output circuit so that that current is proportional to the current flowing through the input circuit.

If you microwaved bean plant seeds over a period of weeks while they were growin…

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If you microwaved bean plant seeds over a period of weeks while they were growing, would they grow faster or longer, and if they would, would that be due to the heat or some effect of the microwave radiation? – DS

Microwaving the bean plant seeds would be no different from heating them, except that the distribution of temperatures in the seeds and soil might be a little different from what you would get if you simply used a space heater. The particles or photons of ultraviolet light, X-rays, or gamma rays have enough energy to cause chemical changes in organic molecules and can induce mutations in living organisms. However, the photons of microwaves have so little energy that all they can do is heat living things. The most likely result of microwaving the bean plant seeds will be that the seeds will overheat and won’t grow at all. You’ll have bean stew.

My mother owns a microwave oven that is about 20 years old. It looks like new an…

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My mother owns a microwave oven that is about 20 years old. It looks like new and has always been well taken care of. However, I was wondering whether it is still safe to use. Should I have it tested for leakage? — KE, Milwaukee, WI

As long as it still cooks, it’s probably fine. Leakage of microwaves can only occur if the cooking chamber has holes in its metal walls. These walls include the metal grid over the front window and the seals around the door. If the metal grid is intact and the door still appears to close properly, the oven shouldn’t leak any more microwaves now than it did 20 years ago. However, to set your mind at ease, you can have it tested or test it yourself. www.comforthouse.com sells a simple microwave leak tester for $30. You can probably find similar devices at local appliance stores or, for a more accurate and reliable test, take your microwave oven to a service shop for inspection with an FDA certified meter. [Note added 1/10/97: I have finally found one microwave oven that leaks enough that a simple tester identifies it as dangerous—it’s the microwave oven in my laboratory and I’ve moved it around frequently and taken it apart several times for my classes. Evidently, I damaged its door hinges during my experiments because the door now sags a bit and doesn’t seal properly. The tester worked nicely in finding the leaks.]

Where does the white go when the snow melts? – JM

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Where does the white go when the snow melts? – JM

To start with, light slows down when it moves from air to ice and speeds up when it moves from ice to air. That’s because the electric charges in matter can delay a light wave and slow it down. Since electric charges are more concentrated in ice than they are in air, light travels more slowly in ice than it does in air. Next, some light reflects whenever light changes speed. That’s why a glass windowpane reflects some light from both its front and back surfaces. Similarly, light reflects from each surface of an ice crystal. Finally, snow is a jumbled heap of ice crystals. These clear crystals partially reflect light in all different directions like billions of tiny mirrors. The result is a white appearance. You see this exact same effect when you look at white sand, granulated salt, granulated sugar, clouds, fog, white paint, and so on. Each of these materials consists of tiny, clear objects that partially reflect light in all directions. Since they reflect all colors of light equally and spread that light in all direction equally, they appear white.

When the snow melts and becomes water, it stops having all those tiny surfaces to partially reflect light. Instead, it has only its top surface and this surface continues to partially reflect light. That’s why you see reflections in the top of a puddle.

Do regular fluorescent lights emit ultraviolet light? If so, how does the ultrav…

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Do regular fluorescent lights emit ultraviolet light? If so, how does the ultraviolet level compare to what we would receive if we were outside? — GF, Barstow, CA

While the electric discharge in the tube’s mercury vapor emits large amounts of short wavelength ultraviolet light, virtually all of this ultraviolet light is absorbed by the tube’s internal phosphor coating and glass envelope. As a result, a fluorescent lamp emits relatively little ultraviolet light. I think that the ultraviolet light level under fluorescent lighting is far less than that of outdoor sunlight.

What is the composition of the phosphors used in fluorescent light bulbs? – M

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What is the composition of the phosphors used in fluorescent light bulbs? – M

The exact composition depends on the color type of the bulb, with the most common color types being cool white, warm white, deluxe cool white, and deluxe warm white. In each case, the phosphors are a mixture of crystals that may include: calcium halophosphate, calcium silicate, strontium magnesium phosphate, calcium strontium phosphate, and magnesium fluorogermanate. These crystals contain impurities that allow them to fluoresce visible light. These impurities include: antimony, manganese, tin, and lead.

How does a telephone switching system work? Why was it so hard to trace telephon…

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How does a telephone switching system work? Why was it so hard to trace telephone calls? In movies we see people pulling wires in order to trace the origin of a call. – AZ

Before the advent of electronic telephone switching systems, the automatic switching was done by electromechanical relays. These remarkable devices were essentially 10-position rotary switches that were turned by a series of electric pulses—the same pulses that were produced by the rotary dial of a telephone. When you dialed a “5”, your telephone produced a series of 5 brief pulses of electric current and one of these relays advanced 5 positions before stopping. Each number that you dialed affected a different relay so that your called was routed through one relay for each digit in the number that you called. To trace a called, someone had to follow the wires from relay to relay in order to determine what position each relay was in. From those positions, they could determine what number had been dialed. The first few digits of the telephone number determine which exchange (which local switching system) was being called, so those first relays were located in the caller’s telephone exchange building. The last few digits determine which number in the answerer’s exchange was being called, so those relays were located in the answerer’s telephone exchange. As you can imagine, finding your way through all those relays and wires in at least two different buildings was quite a job.