How does an internal voltage regulator type auto alternator work and are they an…

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How does an internal voltage regulator type auto alternator work and are they any better than an external regulator type? – H

An alternator is a device that uses rotary motion to generate electricity. As the car engine turns, it spins a magnet (the rotor) in the alternator and this spinning magnet induces electric currents in a set of stationary wire coils (the stator). The alternator’s ability to generate electric currents by spinning a magnet past stationary wires is an example of electromagnetic induction. Induction is a general phenomenon in which a moving or changing magnetic field creates an electric field, which in turn pushes electric charges through a conducting material. Overall, some of the engine’s mechanical energy is converted into electric energy.

The amount of energy given to each electric charge that flows through the wires in the stator depends on the speed with which the magnet turns and the strength of that magnet. Whether it’s internal or external, the voltage regulator monitors this energy per charge—also known as the voltage—to make sure that it’s correct. If not, it adjusts the strength of the alternator’s magnet. It can do this because the alternator’s magnet is actually an electromagnet and its strength depends on how much current is flowing through its wire coils. The voltage regulator carefully adjusts the current flowing through the electromagnet in order to obtain the proper output voltage from the alternator. Actually, the alternator itself produces alternating current, so a set of solid-state diodes converts this alternating current into direct current. A car’s electric system, particularly its battery, operates on direct current. Since the alternator’s operation is the same whether the voltage regulator is inside it or external to it, neither version should be better than the other.

What are watts and amps? – NS

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What are watts and amps? – NS

The watt is the standard unit of power—that is, it’s the way in which we measure how much energy is being transferred to or from sometime each second. 1 watt is equivalent to 1 joule of energy per second. A 100 watt light bulb consumes 100 joules of electric energy each second. Anytime energy moves from one place to another, you can determine how much power is flowing. For example, the food energy in a jelly donut is about 1 million joules, so if you eat 1 jelly donut in 100 seconds, you receive 10,000 watts of power. Since your body only consumes about 100 watts of power while you are resting, it will take you 10,000 seconds to use up all that food energy.

The amp (or ampere) is the standard unit of electric current—that is, its the way in which we measure how many electric charges flow past a certain point each second. 1 amp is equivalent to 1 coulomb of electric charge per second. Since 1 coulomb of electric charge is the charge on 6,240,000,000,000,000,000 protons, even a current of only 1 amp means that a great many electric charges are passing each second. The current passing through a 100-watt light bulb is roughly 1 amp on average, while the current used in starting a car is about 100 amps.

How does a magnetically levitated transit vehicle work?

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How does a magnetically levitated transit vehicle work? — LB, West Palm Beach, FL

Although there are a variety of schemes for magnetically levitating trains, perhaps the most promising is a technique called electrodynamic levitation. In this scheme, the train contains very strong magnets (probably superconducting magnets like those used in MRI medical imaging systems) and it travels along an aluminum track. The train starts out rolling forward on wheels but as its speed increases, the track begins to become magnetic. That’s because whenever a magnet moves past a conducting surface, electric currents begin to flow in that surface and electric currents are magnetic. Thus the moving magnetic train makes the aluminum track magnetic. For complicated reasons having to do with electromagnetic induction, the track’s magnetic poles are oriented so that they repel the magnetic poles of the train—the two push apart. While the track can’t move, the train can and it floats upward as much as 25 cm (10 inches) above the track. Once the magnetic forces can support the train, the wheels are retracted and the train floats forward on its magnetic cushion. To keep the train moving forward against air resistance (and a small magnetic drag force), there is also a linear electric motor built into the train and track. This motor uses additional electromagnets in the train and track to push and pull on one another and to propel the train forward (or backward during braking).

If E=mc2 and we know light exists, why is it that light doesn’t have …

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If E=mc2 and we know light exists, why is it that light doesn’t have infinite mass and consequently why aren’t we all squashed? – M

The equation that you present is a simplification of the full relationship between energy, mass, momentum, and the speed of light, and is really only appropriate for stationary massive particles. In it, E is the particle’s energy, m is the particle’s rest mass, and c is the speed of light. Since light has no rest mass, the previous equation is simply not applicable to it. I should note that this equation is sometimes used to describe moving massive particles, in which case the m is allowed to increase to reflect the increasing energy of the moving particle. But the use of this equation for moving particles and the redefinition of mass as something other than rest mass often leads to confusion.

A better way to deal with moving particles, particularly massless particles, is to incorporate momentum into the problem. The full equation, correct for any particle, is E2=m2c4+p2c2. In this equation, E is energy, m is the rest mass of the particle (if any), p is the momentum of the particle (if any), and c is the speed of light. While light has no rest mass, it does have momentum and it’s this momentum that gives light an energy. Light travels along at the speed of light with a finite momentum and a finite energy. On the other hand, the momentum of a massive particle increases without limit as the particle approaches the speed of light and so does the particle’s energy. Thus massive particles can’t ever reach the speed of light.

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.

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.

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.

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.

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.]

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.