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#128578 - 06/09/03 01:14 PM magnetic circuits
electricman03 Offline
Junior Member

Registered: 06/08/03
Posts: 7
how does a magnetic circuit work? does it make electricity by the conductor moving? also , how are volts measured, by that i mean what does 1 volt equal?

thanks , scott

#128579 - 08/20/03 01:37 AM Re: magnetic circuits
cavil Offline
Junior Member

Registered: 08/19/03
Posts: 6
A volt is the metric unit of electric potential. Formally 1 volt = 1 joule per coulomb
(In short 1 V = 1 J/C).
Potential must always be measured with respect to some reference level. A voltmeter measures the potential difference between the two points to which its probes are attached. This number is the energy (in joules) that one coulomb of charge would acquire if it moved from the higher to the lower potential solely under the action of the electric force. For example, the chemical reactions in a 1.5V battery 'give' each coulomb of charge 1.5 J of energy as they move through the battery from the lower potential to the higher potential.

#128580 - 09/05/03 11:01 AM Re: magnetic circuits
JohnS Offline

Registered: 07/31/03
Posts: 36
Loc: Cleveland, Ohio USA
First of all, why not go to this ite;

And look up the units in question. And remember all electrial units are SI units.

volt (V):

the SI unit of electric potential. Separating electric charges creates potential energy, which can be measured in energy units such as joules. Electric potential is defined as the amount of potential energy present per unit of charge. Electric potential is measured in volts, with one volt representing a potential of one joule per coulomb of charge. The name of the unit honors the Italian scientist Count Alessandro Volta (1745-1827), the inventor of the first battery.

No Scott, the conductor does not move. The electricity it self "moves" or oscillates back and forth. This is known as the frequency. The changing electric field when passing through a conductor will induce a current in the conductor.

Only a changing current can induce a current in an conductor. However, a steady (DC) current can produce a magnetic field. But, a DC magnetic field can not induce a current in a conductor, except when it is rising or collapsing.

A transformer is a perfect example of a changing electric current in the primary winding, producing a changing magnetic field in the transformer core and that in turn inducing a current in the secondary winding. The frequency of oscillation is equal to the frequency of the incoming current. For example, transformers used in power distributuion, the current oscillates at either 50 Hz or 60 Hz depending on location.

And, it is the current (amperes) and not the voltage that produces the magnetic field.

Magnet units:

weber (Wb)

the SI unit of magnetic flux. "Flux" is the rate (per unit of time) in which something crosses a surface perpendicular to the flow. If the something is a magnetic field, then the magnetic flux across a perpendicular surface is the product of the magnetic flux density, in teslas, and the surface area, in square meters. If a varying magnetic field passes perpendicularly through a circular loop of conducting material, the variation in the field induces a electric potential in the loop. If the flux is changing at a uniform rate of one weber per second, the induced potential is one volt. This means that numerically the flux in webers is equal to the potential, in volts, that would be created by collapsing the field uniformly to zero in one second. One weber is the flux induced in this way by a current varying at the uniform rate of one ampere per second. The weber is a large unit and practical fluxes are usually fractions of one weber. (Because of this, when we want to induce an electric potential in a conductor with a changing field, as we do in all electric generators, transformers and electric motors, we loop the conductor into hundreds of coils, thus adding together the small voltages induced in each loop by the changing field.) The unit honors the German physicist Wilhelm Eduard Weber (1804-1891), one of the early researchers of magnetism.

tesla (T)
the SI unit of flux density (or field intensity) for magnetic fields (also called the magnetic induction). The intensity of a magnetic field can be measured by placing a current-carrying conductor in the field. The magnetic field exerts a force on the conductor, a force which depends on the amount of the current and on the length of the conductor. One tesla is defined as the field intensity generating one newton of force per ampere of current per meter of conductor. Equivalently, one tesla represents a magnetic flux density of one weber per square meter of area. A field of one tesla is quite strong: the strongest fields available in laboratories are about 20 teslas, and the Earth's magnetic flux density, at its surface, is about 50 microteslas (┬ÁT). The tesla, defined in 1958, honors the Serbian-American electrical engineer Nikola Tesla (1856-1943), whose work in electromagnetic induction led to the first practical generators and motors using alternating current.

ampere per meter (A/m) or ampere-turn per meter

the SI unit of magnetic field strength. The ampere per meter is also the SI unit of "magnetization" in the sense of magnetic dipole moment per unit volume.

#128581 - 10/01/03 11:08 PM Re: magnetic circuits
cavil Offline
Junior Member

Registered: 08/19/03
Posts: 6
" But, a DC magnetic field can not induce a current in a conductor, except when it is rising or collapsing."

It's easy to induce currents with DC magnetic fields, just move the wire through the steady field. (Michael Faraday 1831)

#128582 - 10/05/03 09:56 PM Re: magnetic circuits
cavil Offline
Junior Member

Registered: 08/19/03
Posts: 6
"And remember all electrial units are SI units"

Not if they are cgs units like statvolts and abamperes.

Fortunately such units are seldom used and most theoretical texts are adopting SI units. But still in use is the "natural system" of units in which the charge of the electron and the speed of light are both unity. This elegant system is used by physicists.


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