magnetic induction

Nikola Tesla was an inventor, discoverer, electrical engineer, mechanical engineer, theoretical and experimental physicist, mathematician, futurist and humanitarian. He is responsible for over ninety percent of the transmission of electrical power the world relies on today thanks to his discovery of the rotating magnetic field. The inventor utilized this discovery in his invention and patent of the first commutatorless alternating current induction motor which changed the future of power transmission. All electrical technology using or generating alternating current today is due to Tesla, without which all our trolley cars, electric vehicles, subways, manufacturing/industrial plants and electrified power lines, which bring power to almost every single electrical appliance/equipment in our homes/work, would be impossible.

Tesla was a Serbian born on July 10, 1856 at midnight in Smiljan, Lika (in what is now Croatia). He was educated at an early age by his parents before attending the Gymnasium Karlovac in Croatia, the Polytechnic Institute in Graz, Austria; and the University of Prague excelling in linguistics, mathematics and sciences. He was a hyper-polyglot who could speak eight languages including: Serbo-Croatian, English, Czech, French, German, Hungarian, Italian, and Latin. He claimed to have had a three-dimensional memory and thought process that tormented him in his youth, but later aided him with building his inventions in his own mind without wasting any physical energy. He was known to be able to recite by heart full books, mathematical formulas and poetry such as Goethe’s “Faust,” Njegoš’ “The Mountain Wreath,” Dante’s “Divine Comedy,” Shakespeare’s “Hamlet,” Byron’s “Childe Harold’s Pilgrimage,” and Pushkin’s “Eugene Onegin.”

In 1881 while walking with a friend in a City Park reciting Goethe’s “Faust,” Tesla first envisioned the rotating magnetic field and his induction motor– complete, perfect, and operable in form. This visualization would represent the same diagrams shown in a lecture given before the American Institute of Electrical Engineers in 1888.

After his revelation, in 1882, Tesla’s began working for a telephone company in Europe, while he worked independently on his induction motor. In 1884, he moved to America in hopes of capitalizing on his new discovery. Initially, Tesla was hired by Thomas Edison, but the famous American inventor was not interested in Tesla’s alternating current system, due to his already strong interest in direct current power transmission. Tesla would continue working for Edison until Edison promised him $50,000 to make improvements on his DC generation plants. After completing the task, Tesla asked to be paid, but Edison denied him his offer and explained that the offer of $50,000 was just an “American joke.” Edison offered Tesla a small raise, but Tesla resigned instead.

After his fallout with Edison, Tesla was offered his own lighting company by some small investors, but unfortunately, they were also not interested in Tesla’s alternating current system. Tesla would invent a new and efficient arc lamp for the company, but would be forced out of the business after completing his work. This was a bitter blow to the young Serbian who resorted to digging ditches for $2 an hour in order to get by in a new country.

Tesla’s luck would soon change in 1887, after he received a chance to demonstrate his system of alternating currents to some financiers with his famous “Egg of Columbus” demonstration. This great event would lead to the filing of his Alternating Current Poly-phase Induction Motor patent. This opened a wide door for the introduction and commercial development of alternating current motors.

Tesla pushed forward building apparatuses equal in productivity to DC motors, forcing the scientific community to recognize his work. Because of this work, in May of 1888, a publication of Tesla’s work was read before the American Institutes of Electrical Engineers. Prior to Tesla’s invention, it was considered impossible to eliminate the brushes and commutators on the old motors, but the introduction of Tesla’s new electrical theory and practice was an obvious departure from the old into the new. It was completely revolutionary yet so simple. The introduction of his new patent would spark a strong interest in American entrepreneur, George Westinghouse, who would later buy Tesla’s patents, and throw all his resources into the development of Tesla’s work. This new industry in power transmission would eventually start a feud between the Westinghouse Company and Thomas Edison’s General Electric Company–known as the “War of Currents" (AC/DC)…

(to be continued…)

21p-s  asked:

hey! i'm doing electric power at school and i'm really confused about which equation to use when you're finding the induced emf? (-n∆flux) / (∆t) or nBA2pif???? thank you!

Hi! Both equations you mention are actually very valid to help you find the induced EMF! Since I am in the midst of making posts about electromagnetism, I’ll go through this is detail.

Although I will use both calculus with vectors and scalar, pre-calc representations, for your level I’d recommend the equations with non-infinitesimal changes (signified by an ‘approximately equal to’ ‘≈’ symbol and a ‘Δ’ symbol in place of ‘d’.)

The first equation

If we consider the first equation for induced EMF you’ve provided, which states that

(equation 1) where N is the total number of turns in a loop of wire, t is time and ΦB is the flux of an inductive magnetic field B through a surface S (which we can define for each situation,) given by

in which: “⋅” represents the scalar (‘dot’) product; ϕ is the angle between the field lines of the magnetic field and the normal to the surface. It is worth noting that the cos ϕ part of the expression comes directly from the scalar representation of the dot product.

This is the most general expression for the induced EMF – describing the effect a changing magnetic field (or a moving/changing surface, for that matter) has on the motion of charges through a circuit. It tells us that when we move a conducting rod through a loop of current-carrying wire, we expect to observe a current induced through the rod since lines of flux are being intersected by our rod (which is our surface, in this case.)

However, if we move our rod through the wire loop—which will, for now, be carrying a DC (i.e. direct current; non-changing) signal—and hold it at the centre, we notice this new current produced by the induced EMF will drop off in proportion with how fast we move it through the field. This is because less lines of flux are being intersected per unit time, signified by the ratio of flux change to time change. This is an important feature of electromagnetic induction because it means that if the current in the first wire is constantly changing, we need not vary the position or dimensions of our rod to allow an induced current.

The second equation

A changing field is produced using an AC circuit, which varies the voltage from a positive value to a negative value within a specific time frame, given by the frequency f of the signal which oscillates over 2π radians, allowing us to define the angular frequency ω = 2πf. This principle is vital to modern life and has applications in communications methods such as Wifi, radar, GPS and Blutooth. I hope to write a set of posts about radio communications in the future but we’ll have to wait and see whether I end up having time!

We can visualise the inductive effects of an alternating current by considering how it is principally generated – using a rotating magnet in a solenoid of N turns (a solenoid is long of wire coiled multiple times to form a sort of wire tube.)

Let’s define our flux surface as the area of a wire loop so we can see the how the flux of the magnetic field through the solenoid. To simplify the situation, we’ll ignore the integration and say that S := A, where A is the cross-sectional area of the solenoid, which means that

It is worth noting the time-dependency of the angle here: our magnetic field source is now rotating, so the angle between the field lines and the surface normal will be changing with time, too! Thus, with a little bit of thinking, we can determine ϕ(t).

We know our magnet, which is producing field lines through its poles, is rotating with an angular frequency ω = 2πf and we know that f = 1∕T, where T is the time period, so

This may help us conceptually when considering the timing of the magnet’s angle, since we can express the time in terms of the total period of the motion.

Let’s say at time t = 0, the magnet has its North pole towards the surface; the angle here is zero, meaning the induced EMF is at a maximum.

One complete revolution later, where t = T, the magnet has returned to its original position and now has ϕ(T) = 2π = 0. Therefore, by substituting the current time for our period we find that

Through rearrangement (multiply both sides by t,) this becomes

and, since we know that ϕ(T) = 2π

and we know that ϕ(T) = ϕ(t), so finally:

This is our time-dependent angle, discovered through inference alone! We can check this for any stage rotation in terms of the period and will find the correct angle. This expression throughout in oscillations throughtout physics.

So,

Now we have to use a little calculus. Recall our original expression for the induced EMF, given by equation 1, and substitute our new expression for the magnetic flux density:

By applying the chain rule, which states that

we find that

and so

which, when evaluated at t = 0 (or t = T, and so on) for maximum EMF, yields the equation you provided:

From following the derivation through, it can be seen that this expression outlines the maximum EMF induced in a wire which follows a regular looping pattern around a cross sectional area A (as with a solenoid of N turns) by a magnetic field density B for some alternating current (or regular oscillation) having a frequency f. This could be used for any AC-based induction, any system involving periodically rotating magnets or something involving periodic changes in solenoid dimensions. The key point here of that this equation requires periodic oscillation oscillation and, evidently, this describes a much more specific scenario than the first equation.

The mathematical derivation itself may be a little difficult to follow as it uses mathematics that you haven’t explicitly met yet but the key concepts lie in the derivation. Just try to understand the scenario outlined and the arguments made so you can know whether a scenario is applicable.

For a little more information, which should be more aimed at the specific syllabus you are studying, see the following posts:

I hope this helps! Let me know if you have any more questions!

“Ahead of His Time: A Mini Biography of Nikola Tesla.

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This mini biography is intended to share the life of Nikola Tesla and the work he produced, in simplistic form. I hope to enlighten the readers on how he developed his inventions and discoveries, and how he envisioned his wildest aspirations for the future.

Enjoy… (((:

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Nikola Tesla was an inventor, discoverer, electrical engineer, mechanical engineer, theoretical and experimental physicist, mathematician, futurist and humanitarian. He is the primary cause for over ninety percent of the transmission of electrical power the world relies on today thanks to his discovery of the rotating magnetic field. The inventor utilized this discovery in his invention and patent of the first commutatorless alternating current induction motor which changed the future of power transmission. All electrical technology using or generating alternating current today is due to Tesla, without which all our trolley cars, electric vehicles, subways, manufacturing/industrial plants and electrified power lines, which bring power to almost every single electrical appliance/equipment in our homes/work, would be impossible.

One could argue that Tesla is responsible for the creation of the Twentieth Century, and the present day we enjoy today. He was the first to demonstrate the transmission of wireless energy, and is the true father of radio. In his labs experiments, he conducted a range of experiments with mechanical oscillators/generators, electrical discharge tubes, photography, electrical therapy, and some of the first X-ray imaging. He was the first to demonstrate remote control, building a wireless controlled boat first exhibited in 1898. At Colorado Springs, in 1899, he created artificial lightning bolts 100 feet long, and sent currents around the Earth from his transmitter and back with a mean velocity of 292,815 miles per second. Although not recognized for, he was the first to discover the electron, radioactivity, terrestrial resonance, stationary waves (scalar waves), and cosmic rays, which he recorded traveling up to fifty times faster than light. Tesla predicted television, the internet, smart phones, weather control, and interplanetary communication. He theorized an idea to produce an artificial Aurora Borealis to light the night skies, and a particle beam to be used for defense in war. He intended to unify all his innovations into one big machine known as his “World System,” but lacked the investments and funds to finish his work on a large scale. His failure to accomplish his goals left him with a distorted persona of a mad scientist, and a dreamer whose imagination created an unrealistic hope for the future. 

Tesla was a Serbian born on July 10, 1856 at midnight in Smiljan, Lika (in what is now Croatia). He was educated at an early age by his parents before attending the Gymnasium Karlovac in Croatia, the Polytechnic Institute in Graz, Austria; and the University of Prague excelling in linguistics, mathematics and sciences. He was a hyper-polyglot who could speak eight languages including: Serbo-Croatian, English, Czech, French, German, Hungarian, Italian, and Latin. He claimed to have had a three-dimensional memory and thought process that tormented him in his youth, but later aided him with building his inventions in his own mind without wasting any physical energy. He was known to be able to recite by heart full books, mathematical formulas and poetry such as Goethe’s “Faust,” Njegoš’ “The Mountain Wreath,” Dante’s “Divine Comedy,” Shakespeare’s “Hamlet,” Byron’s “Childe Harold’s Pilgrimage,” and Pushkin’s “Eugene Onegin.”

In 1881 while walking with a friend in a City Park reciting Goethe’s “Faust,” Tesla first envisioned the rotating magnetic field and his induction motor– complete, perfect, and operable in form. This visualization would represent the same diagrams shown in a lecture given before the American Institute of Electrical Engineers in 1888.

After his revelation, in 1882, Tesla’s began working for a telephone company in Europe, while he worked independently on his induction motor. In 1884, he moved to America in hopes of capitalizing on his new discovery. Initially, Tesla was hired by Thomas Edison, but the famous American inventor was not interested in Tesla’s alternating current system, due to his already strong interest in direct current power transmission. Tesla would continue working for Edison until Edison promised him $50,000 to make improvements on his DC generation plants. After completing the task, Tesla asked to be paid, but Edison denied him his offer and explained that the offer of $50,000 was just an “American joke.” Edison offered Tesla a small raise, but Tesla resigned instead.

After his fallout with Edison, Tesla was offered his own lighting company by some small investors, but unfortunately, they were also not interested in Tesla’s alternating current system. Tesla would invent a new and efficient arc lamp for the company, but would be forced out of the business after completing his work. This was a bitter blow to the young Serbian who resorted to digging ditches for $2 an hour in order to get by in a new country.

Tesla’s luck would soon change in 1887, after he received a chance to demonstrate his system of alternating currents to some financiers with his famous “Egg of Columbus” demonstration. This great event would lead to the filing of his Electro Magnetic Motor patent which utilized the rotating magnetic field principle. Prior to this patent, it was considered impossible to eliminate the brushes and commutators on the old motors, but the introduction of Tesla’s new electrical theory and practice was an obvious departure from the old into the new. It was completely revolutionary yet so simple, and it opened a wide door for the introduction and commercial development of AC motors.

Tesla pushed forward building apparatuses equal in productivity to DC motors, forcing the scientific community to recognize his work. Because of this work, in May of 1888, a publication of Tesla’s work was read before the American Institutes of Electrical Engineers. The introduction of Tesla’s apparatus showed how inefficient the old motors were compared to his own, which utilized poly-phase currents in such a way that made the commutators of the old motors obsolete. This new system would spark a strong interest in American entrepreneur, George Westinghouse, who would later buy Tesla’s patents, and throw all his resources into the development of Tesla’s work. This new industry in power transmission would eventually start a feud between the Westinghouse Company and Thomas Edison’s Electric Light Company–known as the “War of Currents" (AC/DC).   

Compensating off his new patents and now working with the Westinghouse Company, Tesla was finally free to test the limits of his invention on larger scales than before, but to his dismay, the inventor was forced to find ways to build his machines using high frequency electricity instead of the low frequency he was used to in order to better fit his machines with the Westinghouse Company’s production. This presented complications for Tesla, but thanks to his years of study in electricity, Tesla was able to utilize Lord Kelvin’s theory on condenser discharges, which led to the invention of his “Tesla Coil.” With this invention, he was now able to experiment with his work at much higher potentials and frequencies – enabling him to build an AC apparatus of efficiency surpassing that of DC motors.

In 1891, just before becoming an American citizen, Tesla was asked to repeat his experiments before the AIEE. During his lecture, titled “Experiments with Alternate Currents of Very High Frequency and Their Application to Methods of Artificial Illumination,“ Tesla left the audience of America’s greatest engineers spell-bound as he demonstrated by experiments a new theory of light. He demonstrated that incandescent lamps do not require the faulty carbon filament widely used at that time, but could be replaced with a solid block of carbon powered by a single wire branched from his AC generator. Tesla implied that this new application to lamps could be made at little cost, and could be just as dependent and reliable as a gas burner. He went even further and demonstrated that electric light was possible without incandescent lamps. Throughout his investigations of high frequency phenomena, Tesla satisfied himself with a conclusion that an electric field of sufficient intensity could fill a room and light electrodeless vacuum tubes. This would be his first public demonstration of his “art of wireless transmission,” making him the true father of wireless. This was done by connecting two large sheets of zinc to the terminal of the circuit with the sheets being spread apart about fifteen feet away from each other. The sheets served as condensers and both received the charge of electricity from the wires connecting the sheets to the transformer, creating an electric field between the two. Tesla introduced a glass tube from which the air had been exhausted, and,when this vacuum tube was placed between the zinc sheets, it gave out a bright illumination sufficient to light a room. Tesla waved the tube around freely, like a Jedi showcasing the first light saber, and the tube continued to glow as long as it remained in the electric field. The electrical wizard went on to show the absolute harmlessness of his electric system by passing thousands of volts of electricity through his body–lighting light bulbs and shooting sparks out of his finger tips. He accomplished this without killing himself by upping the speed of his dynamo, transforming his AC current into a continuous flow of static currents, which allowed him to pass a large amount of energy through his body without any harm. To help better explain this, DC currents carry an electric charge along a conductor which travel in one single direction, like a straight line, while the charge in AC currents alternate back and forth in waveform. Static currents, on the other hand, are stationary with no movement. Tesla would speed up his AC currents so fast that they would transform into a static current, allowing him to safely store this electricity in his body until he discharged it into his light bulbs resulting in illumination.

These amazing demonstrations would set Tesla apart from the rest of the scientific world. The inventor would be showered with awards and invitations from all around the world begging him to share his work. In 1892, he would finally be persuaded to give two lecturers in London, and one in Paris before returning to America to continue his work.

Back in America, Tesla and George Westinghouse remained consistent in their fight to market their new AC system, despite the heavy smear campaign conducted by Thomas Edison to show the dangers of AC. Edison went as far as holding public demonstrations using AC to electrocute dogs, cats and an elephant to prove his point. He is also responsible for the creation of the electric chair, in 1890. Edison did everything he could to make sure history remembered him and not Tesla, and it is rumored that Edison spent a fortune every year trying keep his own name before the public. Regardless of his inhumane campaign, it still didn’t take away the fact that AC was more efficient than DC. In 1892, the General Electric Company merged with another rival of the Westinghouse Company, the Thomson-Houston Electric Company. This merger would introduce some major competition for the Westinghouse Company since this new formed company now controlled three quarters of the electrical business in the United States. In 1893, the Westinghouse Company caught a break and was contracted to power the World’s Colombian Exposition, in Chicago. Tesla’s Poly-phase System installed at the exposition made certain that AC was superior to DC, ensuring the Westinghouse Company the contract to harness Niagara Falls. This would put an end of the “War of Currents” and force businesses to accept the new system. Since the AC patents were controlled by the Westinghouse Company, Elihu Thomson, the manager of the Thomson-Houston Electric Company, hired Charles Steinmetz in hope that both could somehow bypass Tesla’s AC patents and secure their own AC system that would allow General Electric to compete with the Westinghouse Electric Corporation. Their jobs were basically reduced to finding ways to pretend like they created a new invention. In order to do so, they paid a janitor to steal Tesla blueprints from the Westinghouse plant in Pittsburgh. After the Thomson-Houston company was caught committing industrial espionage, they claimed that “they needed to study Tesla’s motor designs to make sure their’s were different.” Embarrassed by his actions, Steinmetz deliberately omitted Tesla from his major works including “Theory and Calculations of Alternating Current Phenomena,” and “Theoretical Elements of Electrical Engineering.” The associates of General Electric gave Tesla no reference at all in their works which made them popular, even though Tesla was the forefront of the field, and his book, “The Inventions, Researches, and Writings of Nikola Tesla” was basically a Bible for electrical engineers at that time. Elihu Thomson, Charles Steinmetz, Mihajlo Pupin, Thomas Edison and others basically took a huge shit on Tesla because they despised him and wanted him forgotten.

Regardless of the drama, Tesla carried on with his work. Now financially comfortable and free to experiment as he pleased, Tesla vigorously continued his investigations into the unknown…

(To be continued…)

4

Magnetic induction - the levitating bbq

At the Palais de la Decouverte in Paris, a 1kg aluminium plate is levitated above a large coil of wire that is being supplied with 800A of alternating current at 900Hz.

Note the flare of the globes on the lamp when he moves it into the magnetic field and the steam coming off the surface - it’s also humming with the frequency of the alternating current. If you have time I recommend watching the video - it is very entertaining.

Video source

“One afternoon I was walking with a friend in the City Park and reciting poetry. At that time I knew entire books by heart, word for word. One of these was Goethe’s “Faust;” and the setting sun reminded me of the passage:

“The glow retreats, done is the day of toil; It yonder hastes, new fields of life exploring; Ah, that no wing can lift me from the soil, Upon its track to follow, follow soaring!“

“Even while I was speaking these glorious words, the vision of my induction motor, complete, perfect, operable, came into my mind like a flash. I drew with a stick on the sand the vision I had seen. They were the same diagrams I was to show six years later before the American Institute of Electrical Engineers. My friend understood the drawings perfectly; and to me the images were so real that suddenly I cried, “Look! Watch me reverse my motor!” And I did it, demonstrating with my stick.

This discovery is known as the “rotating magnetic field.” It is the principle on which my induction motor operates.”

–Nikola Tesla

“Making Your Imagination Work For You.” American Magazine, April, 1921.

Requested Anonymously

Radio, television, and wifi are all forms of long-distance electromagnetic communication. They all use electromagnetic waves of various wavelengths to send signals through free space. However, these signals use electric fields and antennae to communicate. Beldum uses a magnetic field to talk to others of its kind.

Using a magnetic field to send signals is known as near-field magnetic induction communication, or NFMIC. It’s inherently different than radio or wifi signals for a few reasons, the most significant being the first letter–near. Radio and wifi waves propagate over long distances and through free space. NFMIC signals exist only within a localized magnetic field.

The first step to NFMIC is to create a magnetic field then. In long-distance signals, antennae are used to emit EM radiation that contains the message (see Dedenne). In typical NFMIC, coils are used to create a magnetic field. The energy of the field can create electromagnetic waves much like an antennae, typically with wavelength a frequency in the same range as radio, television, and wifi waves. Again, unlike other kinds of communications which go out into free space, the signal only exists inside of the magnetic field.

So that’s how beldum communicates with others of it’s kind. It connects to others via generating a magnetic field, and sends electromagnetic pulses to each other using radio waves inside of the field. 

The other part of beldum’s pokédex entry states that beldum actually doesn’t have blood, but rather a magnetic force. At first, this doesn’t seem to make sense. Blood is a physical liquid, and magnetism is a force. Substituting blood for magnetism would be like substituting a meal in exchange for a game of bowling. It’s comparing apples and oranges, but even more extreme. You can’t satisfy hunger and gain nutrients by knocking down bowling pins. You can’t transport oxygen and fight off viruses with a magnetic force.

But that doesn’t mean the pokédex is lying. Beldum is a fairly funky pokémon, almost more robot than animal. And if that’s the case, it wouldn’t need blood. Robots wouldn’t need to breathe or eat or transport nutrients, so they don’t need a bloodstream. They do, however, need wires and capacitors to move electricity to their various limbs. This is where the magnetism comes in. Moving charges (electric current) create magnetic fields, and magnetic fields can push charges along.

Actually, every animal (including humans) has electrical signals coursing through their bodies. Our nervous system is nothing but a series of electrical signals that lets us move our muscles, feel pain, and in general makes us function. Our entire brain consists of these little electronic signals firing off–that’s what makes thinking possible.

So beldum doesn’t have to be a robot at all: it simply has magnetism coursing through its nervous system, controlling its body and letting it communicate with others of its species. This whole electrical system runs its body and makes it “alive”, even if it doesn’t have blood. Lots of organisms don’t have blood: jellyfish, plants, algae, fungi, microbes and so on.

Beldum uses near-field magnetic induction communication to talk with others of its species. It’s nervous system is run by magnetic energy, and it doesn’t have blood.

When I was a boy of seven or eight I read a novel titled “Abafi"—The Son of Aba—a Servian translation from the Hungarian of Josika, a writer of renown. The lessons it teaches are much like those of “Ben Hur,” and in this respect it might be viewed as anticipatory of the work of Wallace. The possibilities of will-power and self-control appealed tremendously to my vivid imagination, and I began to discipline myself. Had I a sweet cake or a juicy apple which I was dying to eat I would give it to another boy and go through the tortures of Tantalus, pained but satisfied. Had I some difficult task before me which was exhausting I would attack it again and again until it was done. So I practiced day by day from morning till night. At first it called for a vigorous mental effort directed against disposition and desire, but as years went by the conflict lessened and finally my will and wish became identical. They are so to-day, and in this lies the secret of whatever success I have achieved. These experiences are as intimately linked with my discovery of the rotating magnetic field as if they formed an essential part of it; but for them I would never have invented the induction motor.
— 

Nikola Tesla

“Some Personal Recollections.” Scientific American, June 5, 1915.