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From Wikipedia

Choke (electronics)

A choke is an inductor designed to block (have a high reactance to) higher frequencies in an electrical circuit while passing signals of much lower frequency or direct current.

Description

Choke coils are inductances that isolate AC frequency currents from certain areas of a radio circuit. Chokes depend upon the property of self-inductance for their operation. They can be used to block alternating current while passing direct current (contrast with capacitor).

Common-mode choke

Common-mode choke coils are useful in a wide range of prevention of electromagnetic interference (EMI) and radio frequency interference (RFI) from power supply lines and for prevention of malfunctioning of electronic equipment. They pass differential currents (equal but opposite), while blocking common-mode currents.

Types and construction

Chokes used in radio circuits are divided into two classes – those designed to be used with audio frequencies, and the others to be used with radio frequencies. Audio frequencycoils, usually called A.F. chokes, can have ferromagneticiron cores to increase their inductance. Chokes for higher frequencies often have iron powder or ferrite cores (see Ferrite bead). Chokes for even higher frequencies have non-magnetic cores and low inductance simulating the effects of an air-core.

Solid-state chokes

Solid-state chokes (SSC) can manage higher currents than traditional chokes. They can help reduce the high frequency buzzing noises that occur when running under high electrical currents.


Magnetic circuit

A magnetic circuit is made up of one or more closed loop paths containing a magnetic flux. The flux is usually generated by permanent magnets or electromagnets and confined to the path by magnetic cores consisting of ferromagnetic materials like iron, although there may be air gaps or other materials in the path. Magnetic circuits are employed to efficiently channel magnetic fields in many devices such as electric motors, generators, transformers, relays, lifting electromagnets, SQUIDs, galvanometers, and magnetic recording heads.

The concept of a "magnetic circuit" exploits a one-to-one correspondence between the equations of the magnetic field in an unsaturated ferromagnetic material to that of an electrical circuit. Using this concept the magnetic fields of complex devices such as transformers can be quickly solved using the methods and techniques developed for electrical circuits.

Some examples of magnetic circuits are:

Magnetomotive force (MMF)

Similar to the way, that EMF drives a current of electrical charge in electrical circuits, magnetomotive force (MMF) 'drives' magnetic flux through magnetic circuits. The term 'magnetomotive force', though, is a misnomer since it is not a force nor is anything moving. It is perhaps better to call it simply MMF. In analogy to the definition of EMF, the magnetomotive force \scriptstyle \mathcal{F} around a closed loop is defined as:

\mathcal{F}=\oint \mathbf{H} \cdot d\mathbf{l}.

The MMF represents the potential that a hypothetical magnetic charge would gain by completing the loop. The magnetic flux that is driven is not a current of magnetic charge; it merely has the same relationship to MMF that electric current has to EMF. (See microscopic origins of reluctance below for a further description.)

The unit of magnetomotive force is the ampere-turn (At), represented by a steady, direct electric current of one ampere flowing in a single-turn loop of electrically conducting material in a vacuum. The gilbert (Gi), established by the IEC in 1930 [http://www.iec.ch/about/history/], is the CGS unit of magnetomotive force and is a slightly smaller unit than the ampere-turn. The unit is named after William Gilbert (1544–1603) English physician and natural philosopher.

\begin{matrix}1\,\operatorname{Gi} & = & {\frac {10} {4\pi}} \ \mbox{At} \\ & \approx & 0.795773 \ \mbox{At}\end{matrix}

The magnetomotive force can often be quickly calculated using Ampere's law. For example, the magnetomotive force \mathcal{F} of long coil is:

\mathcal{F} = N I,

where N is the number of turns and I is the current in the coil. In practice this equation is used for the MMF of real inductors with N being the winding number of the inducting coil.

Magnetic flux

An applied MMF 'drives' magnetic flux through the magnetic components of the system. The magnetic flux through a magnetic component is proportional to the number of magnetic field lines that pass through the cross sectional area of that component. This is the net number, i.e. the number passing through in one direction, minus the number passing through in the other direction. The direction of the magnetic field vector B is by definition from the south to the north pole of a magnet inside the magnet; outside the field lines go from north to south.

The flux through an element of areaperpendicular to the direction of magnetic field is given by the product of the magnetic field and the area element. More generally, magnetic flux Φ is defined by a scalar product of the magnetic field and the area element vector. Quantitatively, the magnetic flux through a surface S is defined as the integral of the magnetic field over the area of the surface

\Phi_m = \int \!\!\!\! \int_S \mathbf{B} \cdot d\mathbf S.

For a magnetic component the area S used to calculate the magnetic flux Φ is usually chosen to be the cross-sectional area of the component.

The SIunit of magnetic flux is the weber (in derived units: volt-seconds), and the unit of magnetic field is the weber per square meter, or magnetic fields. In electrostatics, the charges are stationary, whereas here, the currents are steady or dc(direct current). As it turns out magnetostatics is a good approximation even when the currents are not static as long as the currents do not alternate rapidly.

Applications

Magnetostatics as a special case of Maxwell's equations

Starting from Maxwell's equations and assuming that charges are either fixed or move as a steady current \vec{J}, the equations separate into two equations for the electric field (see electrostatics) and two for the magnetic field. The fields are independent of time and each other. The magnetostatic equations, in both differential and integral forms, are shown in the table below.

The first integral is over a surface S with oriented surface element d\vec{S}. The second is a line integral around a closed loop C with line element \vec{l}. The current going through the loop is I_\text{enc}.

The quality of this approximation may be guessed by comparing the above equations with the full version of Maxwell's equations and considering the importance of the terms that have been removed. Of particular significance is the comparison of the \vec{J} term against the \frac{\partial \vec{D}} {\partial t} term. If the \vec{J} term is substantially larger, then the smaller term may be ignored without significant loss of accuracy.

Re-introducing Faraday's law

A common technique is to solve a series of magnetostatic problems at incremental time steps and then use these solutions to approximate the term \frac{\partial \vec{B}} {\partial t}. Plugging this result into Faraday's Law finds a value for \vec{E} (which had previously been ignored). This method is not a true solution of Maxwell's equations but can provide a good approximation for slowly changing fields.

Solving magnetostatic problems for currents

If all currents in a system are known (i.e. if a complete description of \vec{J} is available) then the magnetic field can be determined from the currents by the Biot-Savart equation:

\vec{B}= \frac{\mu_{0}}{4\pi}I \int{\frac{\mathrm{d}\vec{l} \times \hat{r}}{r^2}}

This technique works well for problems where the medium is a vacuum or air or some similar material with a relative permeability of 1. This includes Air core inductors and Air core transformers. One advantage of this technique is that a complex coil geometry can be integrated in sections, or for a very difficult geometry numerical integration may be used. Since this equation is primarily used to solve linear problems, the complete answer will be a sum of the integral of each component section.

For problems where the dominant magnetic material is a highly permeable magnetic core with relatively small air gaps, a magnetic circuit approach is useful. When the air gaps are large in comparison to the magnetic circuit length, fringing becomes significant and usually requires a finite element calculation. The finite element calculation uses a modified form of the magnetostatic equations above in order to calculate magnetic potential. The value of \vec{B} can be found from the magnetic potential.

Strongly magnetic materials

Strongly magnetic materials (i.e.,Ferromagnetic, Ferrimagnetic or Paramagnetic) have a magnetization that is primarily due to electron spins. In such materials the magnetization must be explicitly included using the relation

\vec{B} = \mu_0(\vec{M}+\vec{H}).

Except in metals, electric currents can be ignored. Then Ampère's law is simply

\nabla\times\vec{H} = 0.

This has the general solution

\vec{H} = -\nabla U,

where U is a scalar potential. Substituting this in Gauss's law gives

\nabla^2 U = \nabla\cdot\vec{M}.

Thus, the divergence of the magnetization, \nabla\cdot\vec{M}, has a role analogous to the electric charge in electrostatics.

Here "magnetostatic" is a misnomer, since the modified magnetostatic equations can be applied even to fast magnetic switching events where the magnetization is reversing itself in nanoseconds or faster.


Photon belt

The Photon Belt (also called the Photon Band, Photon Ring, Manasic Ring, or Golden Nebula) is a pseudo-scientificbelief, largely linked to some parts of the New Age Movement. It postulates that a belt or ring of photons is going to envelop the Earth, causing a cataclysm and/or initiating a spiritual transition ( referred to variously as a "shift in consciousness," the "Great Shift," the "Shift of the Ages," the "Zero Point," or the "Ascension Point"), with the time period leading up to "the Shift" referred to as "The Quickening." The concept of the Photon Belt also ties in to various prophecies including the Mayan Long Count Calendar, extraterrestrial life, and 2012 millenarianism.

The core of the Photon Belt beliefs is that there is an immense belt of photons orbiting around the Pleiades. According to some New Age beliefs, Earth will pass though this belt of photons, resulting either in humanity's elevation to a higher plane of existence, the end of the world, or both. Authors Virginia Essene (born 1928) and Sheldon Nidle (born 1946) write that the Photon Belt represents a temporary window for spiritual transition during which time humans can reach a higher level of existence, which they term the "galactic" level.

The concept of the Photon Belt was first presented in 1950 by Paul Otto Hesse ( died 1958 ) in his work Der Jüngste Tag ( The Last Day ). This concept was repeated and expanded upon by Samael Aun Weor in a lecture he gave in 1977 titled "The Rings of Alcyone," but the Photon Belt didn't become popular in New Age circles until August 1981, when an article on the topic titled "And So Tomorrow" by Shirley Kemp was published in the Australian International UFO Flying Saucer Research Magazine.

History

Original texts

German engineer and esotericist Paul Otto Hesse ( died Dec. 30, 1958 ) described his beliefs about the Photon Belt and its impact on humanity and planet Earth in his book Der Jüngste Tag ( First Edition, 1950 ) ( English: The Last Day ). The concept of the Photon Belt was further developed by Samael Aun Weor ( Víctor Manuel Gómez Rodríguez ) ( 1917-1977 ) in his lecture "The Rings of Alcyone ( 1977 ) ( original transcript title: "Conferencia Sobre Alcione" ).

In his lecture "The Rings of Alcyone" Weor states the following ( citing Paul Otto Hesse ):

"If the Earth enters [the Photon Belt] first, everything will look like a great blaze, like real pictorial fireworks. But if the Sun were to enter [the Photon Belt] first, according to the calculations that have been made, a radiation would interfere with the solar rays and for this reason there would be a darkness that would last 110 hours, after which everything would return to normal and, unlike the first case, in which everything would look like a great blaze, in the second case, darkness would envelope the Earth. But there would be no darkness really, because everything would be sprinkled with lights; to give you an idea, it would be like a rainfall of stars upon the face of the Earth. Afterwards, everything would return to normal. In any case, our Earth, deep within Alcyone's rings, will be submitted to a very special radiation. The molecules, these being iron, phosphorus, calcium, copper, nitrogen, carbon, starch, etc., etc., would be completely modified due to this radiation. This means that you will see a change in matter."

Weor refers to the Photon Belt as "Alcyone's rings" ( or "the rings of Alcyone" ). Weor claims that "Alcyone is the principal sun of the Pleiades and in its orbit gravitate seven suns, our sun being the seventh which circles Alcyone." According to Weor, Alcyone has rings made of "radiation" caused by the "splitting of the electron." Weor refers to this "radiation" as "manasic" ( from the Sanskrit term for the mind, manas ), and indicates that "it in some way relates to [the distinction between] the inferior manas ( lower mind or lower self ) and the superior manas ( higher mind or Higher Self )." Weor purports that "the electrons in Alcyone's rings release a type of unknown energy".

Elsewhere in his lecture "The Rings of Alcyone" Weor states the following:

"Thereabout, in the year of 1974, three astronauts who were circling the Earth reported a type of radiation, or a type of unknown energy, unsuspected by official science. Obviously, since 1962, specifically since the 4th of February of that year, our planet Earth, and in general, the whole solar system, has been on the verge of entering the terrible rings of Alcyone ... These rings extend for some light years; they are instantly enormous. Nevertheless, at any given moment, our solar system will enter Alcyone’s rings."

Popularity in New Age circles

The Australian International UFO Flying Saucer Research Magazine, Issue #12 ( August 1981 ) published an article on the Photon Belt by Shirley Kemp titled "And So Tomorrow." About 10 years later, Kemp's article was reprinted in Nexus Magazine ( Vol. 2, No. 2 ) under the title "The Photon Belt Story." According to the late Colin Norris (former head of AIUFOFSR, the organization that publishes Australian International UFO Flying Saucer Research Magazine), Kemp's article was actually co-authored by Kemp and a young university student who later became employed as a physicist at a well-known nuclear facility. It appears that Shirley Kemp was serving as librarian for the AIUFOFSR at the time her article was published in the organization's magazine, and that the young university student who co-authored the article was also a member of AIUFOFSR at that time ( August 1981 ).It was Kemp's article which made the topic of the Photon Belt popular in New Age circles. Kemp's article doesn't mention Samael Aun Weor, but it does briefly discuss the contributions of the following scholars, scientists, and astronomers to subjects such as the Pleiades, photons, and the Photon Belt: Nostradamus, Sir Edmund Halley, Friedrich Wilhelm Bessel, Josep Comas Solá, German engineer and esotericist Paul Otto Hesse ( died Dec. 30, 1958 ), Paul Adrien Maurice Dirac, Carl David An


From Yahoo Answers

Question:I'm really stuck... I have performed 3 tests, a no load test a blocked rotor test as well as a load test and i was wondering what equations to use to calculate the equivalent circuit?(ie the values of resistors and inductors shown in this image http://www.ele.auckland.ac.nz/~kacprzak/Image56.gif)

Answers:Don't you have an electric machinery text book? The calculations involve about a dozen equations and a half dozen supporting equations. You need a basis on which to assume how to divide the total blocked rotor reactance into X1 and X2. In the text that I have, the proportions range from .3/.7 to .5/.5 depending on NEMA design class. Did you perform a DC stator resistance measurement? The core loss conductance is assumed to be zero (infinite resistance in parallel with Xm). Here are some notes as a PDF file: http://www.watri.org.au/~zhub/tut/elec3305%202009/Tut%201-6/induction%20machine%20tests.pdf

Question:I mean with or Without Enamel and Varnish. Would thicker copper wire make for a better magnet at high voltages? Whats the difference between using Think and thick copper wire? Also..what about the core? isit better to have a metal core or a AIR core or any other Core you can suggest? Thanks Thin instead of Think``

Answers:You need insulated wire to avoid the turns shorting each other. varnished wire, "magnet wire" is best. Iron core is much better than air core. Thick wire allows more current to flow while minimizing losses. But thicker wire doesn't allow as many turns, and the more turns the more magnetic field. But the more current also increases the magnetic field. So it's a compromise between thick and thin. The size depends on a lot of factor like number of turns and battery voltage and desired field. wikipedia: A magnetic core is a piece of magnetic material with a high permeability used to confine and guide magnetic fields in electrical and electromechanical devices such as electromagnets, transformers, electric motors, and inductors. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a coil of wire around the core that carries a current. The presence of the core can increase the magnetic field of a coil by a factor of several thousand over what it would be without the core. .

Question:1. What causes the movement of the lithospheric plates? 2. How can the density of the Earth be calculated? 3. How does the density of the Earth provide evidence that the interior of the earth is denser than the surface? 4. Name three main layers of the Earth. 5. Why is the inner core of the Earth solid, even though it is hot? 6. How are convection currents set up? 7. What part of the Earth's interior layers are in motion due to density differences? Thank you so much.

Answers:1. Litho means earth or stone. The lithospheric plates are basically floating on the underlying magma. In thin areas of the plate (hot spots) or areas of stress and fractures, magma will flow up and push the plates apart. When plates collide, one may go under the other (subduction zone) or just crumple together and form mountains (the Himalayas). See also #7 currents will push plates around also. 2. Gravitational pull is based on the mass of an object. A planet with low gravitational pull will be less dense than a planet of the same size (volume) with higher gravitational pull. 3. If you determine the density of the Earth to be 1, and average density of material on the surface is .5, then you can infer that material within the Earth is denser, so that it averages out to 1. Also the Earth's magnetic field reveals that the Earth must contain molten iron and other heavy metals. 4. Lithosphere, Mantle and Core. 5. The tremendous pressure that is exerted on the core causes it to be a solid. Like a pressure cooker allows water to reach a higher temp before it changes from a liquid to a gas, pressure in the Earth prevents the core from changing from a solid to a liquid. Known as a change of phase. 6. Heat rises and cold sinks, within the Mantle same as ocean currents and air currents. Hot is lighter than the same material when it is cold, as it expands and becomes less dense 7. The mantle is in motion just like ocean and air currents. Cooler mantle sinks, then the pressure at depth heats it up and it rises. It just keeps circulating.

Question:The complete collapse of the Twin Towers has more to do with the construction than anything else. Yes, it was the loss of fireproofing and subsequent fires that collapsed the building but if it were not for the construction, a total collapse may not have occurred. Ironically, the construction also saved many lives by letting the towers stand as long as they did. These pages explain the construction and provide evidence for collapse by fire. "Tube in a Tube" The designers coined the term "Tube in a Tube" to describe the buildings construction. The design was an innovation of its day. Thick steel columns ran up the middle of the building. This housed the elevators, stairwell, electrical conduits, water, sewer and other services which ran up and down the length of the buildings. For you to understand the collapse, you will have to remember four main elements. Core columns Perimeter columns Floor Trusses Fire proofing The columns of the building normally found evenly spaced out on a given floor became the outer wall of the building. This left large open areas for renting. A good explanation of this can be found on PBS. Instead of encasing each column in heavy concrete, (normal fire proofing) the designers relied on 'sprayed on' fire proofing with a 2 hour rating to protect the load bearing columns and trusses from fire. Each WTC tower was essentially bolted together like an erector set. Each average floor had 376 5/8" bolts, 188 Truss seats, 120 ViscoElastic pieces and 120 gusset plates. Below is a diagram of the truss system with connections. Trusses connected Perimeter columns to the core. Without this connection neither one could stand alone. Note how the columns are constructed in threes known as column trees. Each column is bolted onto the column beneath and to the tree beside it. There was a 3 to 4 inch layer of concrete on the average floor. There were reinforced concrete floors in the core as well. Contrary to what some conspiracy theorists say, the core walls were NOT concrete reinforced. This was an error made by a news organization which grew a life of its own. The fire proofing was sprayed on after the steel went up. This is called "Passive" fire proofing. Here is a photo of the core sub levels during construction. You can see just how deep below ground level the buildings went. This type of construction makes a very open floor plan. There is a big difference between this type of construction and others like the Landmark Towers in Fort Worth, Texas, which is often used as a comparison by conspiracy theorists. There are large I-Beam columns encased in concrete. Large I-Beams also hold up the floors. The photo below was taken during preparations to demolish the building. Note the vertical column above still has some concrete around it. The Windsor Tower in Madrid is similarly built but with a concrete reinforced core added. Now you have the general idea of the differences in construction between the towers and other high rise buildings. So why did it collapse the way it did? A major factor was the fire proofing on the impact floors. The impact blew off the fire proofing as in the above PBS special. Sources: http://www.debunking911.com I'm hearing a great deal of rhetoric from our "conspiracy theorists", but little fact. I thought you could debunk anything that disproved 9/11 being a government conspiracy! Austingirl: Nice try! But once again, no cigar. If you check prior posts from approx. two days ago, I provided the mathmatical calculations that explain the speed at which the buildings pancaked. You are basing your info on "Loose Change" or some other site that simply doesn't understand the science. If you have a "credible", "scientific" source, I will be happy to take a look at it. Austingirl: I visited your recommended site. But when I clicked on their "Resources and References", there was nothing there. Interesting don't you think!

Answers:The conspiracy nuts won't read your q I bet. But thanks for posting it.

From Youtube

MIT Physics Demo -- Resonant RLC Circuit :A variable capacitor (C), large inductor or solenoid (L), and 200W light bulb (R) are connected in series to 120 VAC. The inductance of the inductor can be varied by inserting an iron core, and the capacitance can be varied by a row of switches. By varying the inductance and capacitance, we can achieve the resonance of the circuit, where maximum current flows through the resistor (light bulb). See the original post on MIT TechTV - techtv.mit.edu

Physics Demo -- Jumping Ring :A solid metal ring is placed on an iron core whose base is wrapped in wire. When DC current is passed through the wire, a magnetic field is formed in the iron core. This sudden magnetic field induces a current in the metal ring, which in turn creates another magnetic field that opposes the original field. This causes the ring to briefly jump upwards. If there is a cut in the ring, it cannot form current inside it, and thus will not jump. When the ring is cooled in liquid nitrogen, the resistance of the metal is lowered, allowing more current to flow. This lets the ring jump higher. However, the magnetic field curves away at the top of the iron coil, meaning with DC power, the ring will never fly off the top. When AC current is passed through the wire, the ring flies off the top of the iron core. This is due to the fact that the current lags the emf by 90 degrees in inductors (which is what we have here). This yields forces on the ring that are always pointing upwards, even as the current oscillates. Original posting on MIT TechTV - techtv.mit.edu