We Wikipedia editors write articles for selfish motives.
This is understandable. We are not being paid to do this. For academically/scientifically/technologically-oriented editors (geeks) like me, who fancy ourselves as "experts" in some subject, the rewards are usually a combination of learning more about our favorite subjects in the course of preparing to write articles, and showing off (in a nice way) our expertise writing about the subjects we are knowledgeable in, feeding our ego.
There's nothing wrong with this, most of the time. It is why WP is so phenomenally successful; it is a "win-win", the ego rewards attract knowledgeable experts to write content for free that they would otherwise have to be paid for, and our readers reap the benefits. The problem comes when these essentially selfish motives conflict with the requirements of writing a good encyclopedia article. The issue is that, by the very fact that we edit articles we are interested in or have expertise in, we editors do not represent a "generic" or "average" reader of the article. Our view of the article, and its subject, and its readers, is inevitably going to be that of an insider, an expert, a hobbyist, a partisan, a fan, or at least an interested aficionado.
This affects our writing. If we are experts, our interest may lie mainly in more abstruse, advanced areas of the subject, and we may be bored with the basic stuff that goes in the introductory sections. On the other hand we may know the subject as a hobbyist, or a member of a fandom, and write for that perspective. Almost always it means we have trouble viewing the article with the fresh eyes of a "neophyte", an unknowledgeable person. But it is vitally important that we do so. Because here is a dirty little secret. Most of the readers of an article will be laypeople who are not knowledgeable in the subject, and don't want to be. 95 out of 100 readers will not read beyond the introduction, and many will only look at the first paragraph. They want only the simplest, most basic information about the topic.
I know, I know. It's difficult to accept the fact that 99 out of 100 readers won't even look at that beautiful elegant proof you wrote in the third section.
"Horse manure", you say. "Knowledgeable people are just as likely to come to an article as neophytes. And other people are going to be just as interested in that fascinating specialized aspect I wrote that long advanced polysyllabic 7 paragraph section on, as I was."
Are they? Be honest. How do you use Wikipedia when you are not editing, when you are actually looking for information? Do you rely on it for expert information on topics you are knowledgeable in? Or do you use it more for general reference?
I do. I don't usually rely on WP articles to learn about electrical engineering, my profession. I may look at an article. But for that I have textbooks, and professional journals and websites written by people who do engineering for a living. With all due respect to my editor colleagues, I would rather trust a professional source than take my chances on Wikipedia. What I use WP for is general reference; getting a brief grounding in topics I know nothing about. I have my laptop open when I am listening to the news, or watching television, or reading, and I look up subjects I don't know about. I suspect that is the most common way Wikipedia is used. And I don't often read even to the end of the introduction, much less the body of the article.
But that means it is a lot more important to make the article comprehensible to the layperson than to the expert. And here, of course, is the rub. Many of us editors just don't want to waste time writing the boring introductory stuff for the noobs. We want to write stuff that we are interested in; that will engage and show off our superior intellect and knowledge. In fact we may have forgotten how to see the subject from the point of view of a noob.
It is easy to see the result. The signature of this kind of "selfish" editing is all over Wikipedia, particularly in the introduction, which should be written for general readers if at all possible. The intro of specialized subjects is often skimpy and incomprehensible to lay people, using buzzwords from the field without defining them. Another problem in technical articles is the definition in the lead sentence gets expanded and abstracted to deal with esoteric caveats and special cases until it is totally incomprehensible to general readers. The article will often be unbalanced, covering a particular "trendy" aspect of the topic extensively, but lacking a broad coverage that includes the "unsexy" areas that general readers need to know. The worst is the "drive by" style of editing, where an editor descends on a poor innocent stub, adds a lengthy, highly technical section on one specialized aspect of the subject, and moves on. And always, always, the writing bears the smarmy imprimatur of the insider, the expert, the geek, not the encyclopedia writer.
Here are some examples. For those articles that I have improved the link it to the "before" version:
The timekeeping element in mechanical clocks and watches, the pendulum or balance wheel, is in physics called a harmonic oscillator (resonator). It consists of a mass which is returned to its equilibrium position by a restoring force proportional to its displacement. Its advantage for timekeeping is that it oscillates preferentially at a specific resonant frequency or period independent of the width (amplitude) of swing, dependent only on its physical characteristics, and resists oscillating at other rates. The resonant frequency is determined by the moment of inertia of the resonator and the restoring force: in balance wheels the elasticity of the hairspring, in pendulums gravitational force.
The escapement is a feedback control device, the drive force is triggered each time the resonator reaches a specific point in its cycle. The resonator (pendulum or balance wheel) and escapement together form a mechanical feedback oscillator, analogous to the electronic oscillator circuit in a quartz watch. It is driven by the continuous force (torque) of the timepiece's mainspring or weights, transmitted through the wheel train. The job of the escapement is to apply this force in short pushes to the pendulum or balance wheel to maintain the oscillating motion, with minimal disturbance to the period.
Escapements are challenging to understand because they are bidirectional devices: energy (impulses) to keep the oscillator going passes through the escapement from the wheel train to the oscillator, but timing signals, locking and release of the escape wheel, which control how fast the wheel train and clock hands advance, pass in the opposite direction from the oscillator to the wheel train.
The interaction of the escapement with the oscillator inevitably disturbs the period slightly, and in precision clocks and watches this is often the major cause of inaccuracy. The escapement must interact with the oscillator to perform two functions each swing: when triggered at a certain point in the oscillators swing it releases the clock's wheels to move forward a fixed amount, and it applies an impulse force to the oscillator to replace the small amount of energy lost to friction each cycle.
The resonance of the oscillator is not infinitely "sharp". It has a small natural frequency range around its resonant frequency called the resonance width . In operation the actual frequency of the oscillator can vary randomly within this range in response to variations in the impulse of the escapement, but outside this frequency range the oscillator does not work at all.
The measure of the possible accuracy of a harmonic oscillator as a timekeeper is a dimensionless parameter called the Q factor, which is equal to the resonant frequency divided by the resonance width: . The larger the factor, the smaller the resonance width as a fraction of the resonant frequency so the more precisely the oscillator regulates the rate of the timepiece. The decreases with friction.
The is also equal to 2π times the ratio of the stored energy in the pendulum or balance wheel to the energy lost to friction during each cycle, which is equal to the energy added by the escapement impulse each cycle. So the larger the is, the smaller the energy loss, the smaller the impulse that has to be applied each cycle to keep it oscillating, and the smaller the disturbance to the oscillator's natural motion. The of balance wheels is around 300, that of pendulums is 103 - 105, while that of quartz crystals in quartz clocks is 105 - 106. This explains why balance wheels are generally less accurate timekeepers than pendulums, which are less accurate than quartz clocks.
If the impulse applied by the escapement could be identical and applied at the identical point each cycle, the response of the oscillator would be identical and its period would be constant, and the escapement would not cause any inaccuracy. However this is not possible. There are unavoidable small variations in the drive force applied to the escapement in all timepieces, due to causes such as the mainspring running down, variations in lubrication viscosity with temperature, lubrication drying up, accumulation of dirt and corrosion, changes in friction due to wear, thermal expansion of parts with temperature changes, and "positional error" in watches: changing friction when the watch is turned and the weight of gear wheel arbors presses against bearing surfaces.
Therefore the goal of escapement design is to apply the impulse in a way that minimizes the change in period with changes in drive force. This is called isochronism. In 1826 George Biddell Airy showed that for maximum isochronism the best place in its cycle to apply the impulse to a harmonic oscillator is at its equilibrium position; in a pendulum at the bottom of its swing, and in a balance wheel at its center rest position, where the restoring force of the spring is zero. Airy proved that, if driven by an impulse symmetrical about its equilibrium point, an ideal harmonic oscillator is isochronous; its period is independent of its drive force and amplitude of swing. The best escapements such as the deadbeat and the lever approximate this condition.
Even if the escapement operation were perfectly isochronous, the pendulum or balance wheel itself inevitably has small inherent departures from isochronism, caused by failure of the restoring force to be exactly proportional to amplitude. In balance wheels this is due to small nonlinearities in the balance spring. In pendulums this is due to circular error, a small increase in the period of swing with amplitude.
Since the impulses are the source of error in precision timepieces, in general the more the oscillator is left undisturbed during its cycle by the escapement to swing freely, the more accurate it can be. Escapements are classified by how much of the oscillator's cycle the escapement exerts force (impulse) on it:
A major source of inaccuracy is friction between the sliding parts of the escapement; the escape wheel tooth sliding as it pushes on the pallet. In precision timepieces the pallet surfaces are made of jewels, principally synthetic sapphire, whose ultrahard surfaces have only 10-20% of the coefficient of friction of metal on metal. The surfaces are lubricated to reduce friction further. In the most accurate escapements, such as the detent escapement, the duplex escapement, and the coaxial escapement, the escape wheel tooth moves almost parallel to the pallet during impulse, reducing the friction.
A traditional terminology is used by clockmakers and watchmakers to describe the complex mechanics of escapements:[1][2][3][4]
The usual measure of amplification, gain, the ratio of output power to input power, is difficult to define for a NR device, since it only has one port. In a NR amplifier, the "input power" from the signal source can be negative, the amplifier can dissipate power in the source as well as the load. Instead, amplification is usually measured by "transducer gain", the radio of power output from the amplifier to the maximum power available from the source
In a shunt NR amplifier (right), current from the source iS is divided between the three conductances , , and , with g having a negative sign because the negative resistance acts like a current source[1]
Derivation of transducer gain Using the current divider formula, the current through the load is therefore So the output power is The maximum power from the source is obtained when a load resistance equal to the source resistance. is attached.[1] In that case the current divides equally between source and load resistance[1] |
Thus the transducer gain (in the passband) is[2][1]
The amplifier is stable for , that is for .[2] The gain increases asymptotically as the parallel source and load resistance approaches the point of instability, the negative resistance r.[2] This is different from the behavior of two-port amplifiers,[2] which are normally unconditionally stable.
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You might be interested to know that, in addition to many student papers, I ran across at least one paper published in a scientific journal that included the pseudoscientific fantasies of GLPeterson. This paper: Chaurasia, Dilip; Ahirwar, Santosh (July 2013). "A Review on Wireless Electricity Transmission Techniques" (PDF). Current Trends in Technology and Sciences. 2 (4): 298–300. ISSN 2279-0535. is a cut-and-paste copy of most of the old Wireless power article including the Tesla "Electrical Conduction" section. Although this paper is a piece of schlock written by hacks, I feel sorry for these guys. They undoubtedly looked at the article, saw all GLPeterson's inline citations, and assumed the content was based on reliable sources.
So, in other words, one editor, if he's persistent enough, can get his totally unsupported bogus theories into the engineering technical literature via Wikipedia. Scary. I think removing the pseudoscience added to WP by the Tesla cult is a real service, particularly for students in developing countries who rely on the massive English Wikipedia as a reference source.
=
In physics and mechanics, the moment of inertia of a body is the property which determines its resistance to being rotated, just as a body's mass determines its resistance to linear acceleration. The amount of torque τ (rotational force) required to give a rigid body an angular acceleration of α about an axis is proportional to its moment of inertia I about the axis: τ = Iα
The moment of intertia of a rigid body depends on the body's mass and the distribution of the mass in space; how far the mass is located from the axis of rotation. So the moment of inertia of the same body can be different depending on the axis of rotation. The moment of inertia of a single particle around a given axis is defined as I = mb2, where m is the mass of particle and b is the distance from the particle to the axis of rotation. The moment of inertia of more complicated objects is determined by summing up the moments of inertia of the particles that make up the object. Moment of inertia in the SI system has units of kilogram-meters2.
Telephone repeaters were developed by early telephone carriers in the US and Europe starting around 1903. They are important in the history of science because they were the first use of amplification, and the early repeaters were the first
The need for repeaters arose with long distance telephone lines. As telephone companies extended their trunklines further to link distant cities, they found that the audio signal was distorted and lost power as it travelled down the pairs of long wires. The distortion, caused by reactance on the line, was solved by the addition of loading coils, but the power loss caused by the resistance of the copper wires put a limit of about ___ miles on a telephone line.
The first practical repeater was the Shreeve carbon repeater invented by ____. The carbon microphone, consisting of granules of carbon in a cell between two electrodes, was familiar to telephone companies because it was . Because the carbon microphone does not generate its own output current but acts as a variable resistor to modulate a DC current passed through it from an external source, it can act as an amplifier, producing more AC audio output power than the power of sound waves impinging on it. The Shreeve electromechanical repeater was essentially a speaker driver and carbon microphone coupled together. The weak incoming audio signal passed through a voice coil wrapped around a magnet, vibrating an iron plunger armature. The armature vibrated a diaphragm attached to a cell of carbon granules through which a strong current was passed. This became the current on the outgoing line.
The Shreeve repeater was a very unsatisfactory amplifier. It had an uneven frequency response, with a sharp peak at the resonant frequency of the plunger acoustic system. Second, the carbon microphone produced an inherent electrical noise, which was heard as a roaring sound in the background on the line. Third, the microphone resistance and thus the DC current through it varied with temperature, causing DC offset problems on the line.
Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After the turn of the century it was found that negative resistance mercury lamps could amplify, and they were used.[1] The invention of audion tube repeaters around 1916 made transcontinental telephony practical. In the 1930s vacuum tube repeaters using hybrid coils became commonplace, allowing the use of thinner wires. In the 1950s negative impedance gain devices were more popular, and a transistorized version called the E6 repeater was the final major type used in the Bell System before the low cost of digital transmission made all voiceband repeaters obsolete. Frequency frogging repeaters were commonplace in frequency-division multiplexing systems from the middle to late 20th century...