why magnetic field is sensed by moving charge only ?
88063
The previous correspondent confirmed that only a moving charge is affected by a magnetic field, but didn't actually address the question of *why* that is the case.  I will attempt to do so.  First, realize that electric fields  and magnetic fields are, under the theory of special relativity, two interrelated aspects of the same thing. Like momentum and energy, or space and time, they vary, depending on the reference frame of the observer. The values for the electric and magnetic fields in one reference frame can be transformed to the values for another reference frame by using the Lorentz transformation.\n\nNow, imagine a charge at rest in a given reference frame.  It exerts a force on other charges given by Coulombs' law.  The amount of force it exerts on those other charges depends only on the amount of charge each of our charges has, and the distance between them.  Another way of looking at this is to say our charge sets up an electric field, and the force on the other charges depends only on the strength of the field and the amount of the other charges.\n\nNow imagine that we are looking at this charge from the point of view of a reference frame that is moving with respect to the charge, so that to us the charge appears to be moving.  We take the formula for the force exerted by the charge, apply the Lorentz transformations which we have to use to relate quantities in different reference frames, and lo and behold, we not only get a force that depends on the amount of the other charges, we get a term that depends on the relative velocity of the charges.  What's more, the force of this new term is at right angles to the relative motion.  We identify this new part of the force, the part that depends on relative velocity of the charges, as the magnetic force.  Hence, the magnetic force depends on the relative motion of the charges.
969954
I think that metal detectors just work by setting up a magnetic field. When the apparatus move over a location that has a magnetic material a flux is produced that induces an electric current in the metal detector, activating a sensor.\n\nIf this is the case (i'm 95% sure it is), then the only factors affecting it's quaility would be within the machine itself as far the smallest current that activates the sensor.\n\nHeat and moisture would not change the magnetic field (moisture might theoretically alter the detectors magnetic field a little bit, but certainly not enough to measure). The both give the same result.
152758
The measure magnetic fields with a magnetometer.
88042
Actually, according to my text book (I'm a physics major at the University of Rochester), there is one reported observation of a magnetic monopole in the literature - that of B. Cabrera in 1982.\n\nApparently, magnetic monopoles were first suggested by Dirac in 1929, and are also proposed by a number of GUTs. Dirac showed that relativistic quantum mechanics leads to the quantization of both the electric charge e and the magnetic charge qm. The magnetic charge of a magnetic monopole would be given by:\n\nqm = n(h-bar)c/(2e) where h-bar = (plank's constant)/(2pi), e=the charge on the electron, n=an integer, and c=the speed of light. \n\nThe mass of a magnetic monopole is predicted to be on the order of 10^6 MeV/c^2, and, therefore, far beyond the range of what we can produce in any accellerator. Numerous cosmic ray searches have concluded that the flux is about 10^-15 cm^-2 s^-1 per unit solid angle (in other words, if magnetic monopoles do exist in cosmic rays, they are extroardinarily rare.) As I said before, there is a single reference in my text book to the only purported observation of a magnetic monopole - that of B. Cabrera in 1982.
81207
None of them, coz a magnetic field does not affect static charges.\n\nUnless that was the answer you were looking for, I get a feeling something is amiss in the question.
585103
a positive and negitive charge attact eachother because of the electromagnetic force, which suggests that 2 charged particles will exert a force on eachother.\n\nTo find the magnetitude and direction of the force you use Coulombs law:\n\nF = (1/4πε).(q1q2/|r|²).r
345474
electrostatics, charge need not be 'static' in the sense of unchanging. Instead 'static' implies that the dynamic coupling between electric and magnetic fields can be ignored. In electrostatics we study e-fields, voltage, and charge, but ignore any magnetic fields generated by the motion of these charges or that may be present for other reasons. Because of the electric field's relationship to and interaction with magnetism, electrostatics is a subfield of electromagnetism.\nThe electrostatic approximation\nThe validity of the electrostatic approximation rests on the assumption that the electric field is irrotational:\n\n \n\nFrom Faraday's law, this assumption implies the absence or near-absence of time-varying magnetic fields:\n\n \n\nIn other words, electrostatics does not require the absence of magnetic fields or electric currents. Rather, if magnetic fields or electric currents do exist, they must not change with time, or in the worst-case, they must change with time only very slowly.\n\nIn some problems, both electrostatics and magnetostatics may be required for accuratete predictions, but the coupling between the two can still be ignored.\n\n[edit]\nElectrostatic potential\nBecause the electric field is irrotational,is possible to express the electric field as the gradient of a scalar function, called the electrostatic potential (also known as the voltage). Thus, the electrostatic potential Φ is related to the electric field E by the equation:\n\n \n[edit]\nFundamental concepts\n[edit]\nCoulomb's law\nThe fundamental equation of electrostatics is Coulomb's law, which describes the force between two point charges:\n\n \n[edit]\nThe electric field\nThe electric field (in units of volts per meter) is defined as the force (in newtons) per unit charge (in coulombs). From this definition and Coulomb's law, it follows that the magnitude of the electric field E created by a single point charge Q is:\n\n \n[edit]\nGauss's law\nGauss' law states that "the total electric flux through a closed surface is proportional to the total electric charge enclosed within the surface." The constant of proportionality is the permittivity of free space.\n\nMathematically, Gauss's law takes the form of an integral equation:\n\n \n\nAlternatively, in differential form, the equation becomes\n\n \n[edit]\nPoisson's equation\nThe definition of electrostatic potential, combined with the differential form of Gauss's law (above), provides a relationship between the potential Φ and the charge density ρ:\n\n \n\nThis relationship is a form of Poisson's equation.\n\n[edit]\nLaplace's equation\nIn the absence of unpaired electric charge, the equation becomes\n\n \n\nwhich is Laplace's equation.\n\n[edit]\nStatic charge generation\n[edit]\nCharge separation by contact\nThe presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the triboelectric effect. Rubbing two non-conductive objects generates a great amount of static electricity. This is not just the result of friction; two non-conductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually insulators, i.e., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Some examples of these substances are rubber, plastic, glass, and pith. Conductive objects only rarely generate charge imbalance except, for example, when a metal surface is impacted by solid or liquid nonconductors. The charge that is trans
262366
Yes, but it is a small magnetic field
212659
Electromagnetic fields. In the classical view, a charged particle experiences a magnetic force when it is at some non-zero velocity with respect to a magnetic field. This is in addition to any electric force from any electric field that is present.\nRelativity theory unites these two fields as it reveals that a magnetic field is just what an electric field "looks like" to a charged particle when there are non-zero relative velocities involved.\nQuantum field theory (specifically quantum electrodynamics aka QED) further simplifies this by viewing electromagnetic force interactions as exchanges of "virtual photons".\nAs was said before, depending on the scale of the system, any of the other 3 fundamental forces may non-negligibly affect the particle as well.
118901
Why does it?  Because currents produce magnetic fields in all directions.  In order to use the magnetic field around a closed loop to determine the current flowing through it, you have to consider all the magnetic fields that the current produces.
1041895
when the magnetic needle (a magnet) is places close to any metal, the magnetic field generated by the magnet will cut the metal and causes some electron to move inside the metal, which causes to metal to have different electric charge at each end. now because there is electric charge, it causes an electromagnetic field (EMF). this newly generated EMF interacts with the magnetic field created by the magentic needle and causes it to reflect.\nI remeber doing a physics experiment that illustrates this same effect. we had two small synlindrical metals, one of them was metal the other just normal metal. we put each one of them seperatly from one end of a metal tube and let it fall through to the other end, the metal usually gets from the other side quickly because it is falling free fall in the tube, however, when we put the metal inside it, it took much much longer time for the metal to fall through, the reason, as the magnit is moving (falling down) inside the tube, it is generating a current in the tube which in tern creats a magnetic field which opposes the magnetic field created by the magnet therefor the magnetic field creats a force that tried to repel from the falling magnet and it creates a force that tries to push the magnet up in the tube, of course the gravity is stronger and eventually the magnet comes out from the other end, but it didn't fall a free fall therefor it came out late..\n\nI hope this helps.
91676
I answered your question already.  Magnetic field strength is governed by amount of current flow.
689737
There is a symbol for magnetic fields, which is B and has the unit Tesla.  \n\nGenerally, all forces are represented by F, and you just specify the context in which the force takes place.\n\nFor example:\n\nA charged particle moving through a magnetic field experiences a magnetic force given by:\n\nF = qv X B\n\nWhich is the charge, q, times its velocity v, in a cross product with the magnetic field.  \n\nAlso, there is a an equation for magnetic force between two magnetics that is similar to that of gravity and electricity:\n\nF = Km1m2/r^2\n\nWhere K is the constant, m one and m two are called magnetic moments, and r is the distance between them.  Still, the symbol for the force is just F.
959062
The ions are acceerated through the potential difference V. The kinetic energy they achieve going through that potential is\n\n0.5*m*v^2 = Q*V\n\nwhere m is the mass, v is the speed, Q is the charge, and V is the potential difference.\n\nThe moving charge in the applied magnetic field will result in a force that is at right angles to the motion. The ion will traverse a curved path, and as a result will experience centripetal acceleration. The force of the applied magnetic field (Q*v*B) is balanced by the centrifugal force.\n\nQ*v*B = m*v^2/r\n\nQ*B = m*v/r\n\nUsing v derived from the energy balance above\n\nv = sqrt(2*Q*V/m)\n\nso that\n\nQ*B = (m/r)*sqrt(2*Q*V/m) = sqrt(2*m*Q*V)/r\n\nSolving for the mass m\n\nm = (Q*B*r)^2/(2*Q*V)\n\nsimplifying\n\nm = (0.5*Q/V)*(B*r)^2
441745
When you move the card through the reader pulses of current (not voltage) are generated in the coil(s) which reads your card (the Faraday effect).  The more quickly the card moves through the reader, the higher amplitude current is generated.  If you move the card too slow, the current generated is too small, and then the electronics attached to the read coil(s) cannot see a signal large enough to be detected as pulses which are interpreted as the 1's and 0's of the data on your card.\nTry the first link below and move the magnet slowly and quickly and observe what the difference is on the meter.
31611
Well even though humans have known about magnets for thousands of years, the real reason they work is still somewhat mysterious. Depending on how deep you want to investigate, it can be a very complicated phenomenon. \n\nA magnet is, at its foundation, caused by the movement of electrical charge (yes this is the Biot-Savart Law). When charges (like electrons for example) move, they produce magnetic fields. If a charge moves in a loop, it creates a magnetic field. The magnetic field can be basically represented by an invisible set of arrows in space, that point in a direction. In the case of the loop, the arrows of the magnetic field will point out of the loop for a positive charge moving counter clockwise (this is the so-called "right hand rule"), and into the loop for a charge moving clockwise (some pictures are in the reference attached). \n\nThe magnetic field has a "north" end and a "south end". The little arrows from our moving charge are pointing in the "north" magnetic direction, and away from the "south" magnetic direction. It is a mysterious and interesting property of electromagnetism that two objects with fields that oppose each other, i.e., the little arrows of the field do not line up, so either the north end of one field is facing the north end of the other field, or the two south ends are facing each other, repel, or resist movement of the two objects towards each other with some force. \n\nOn the other hand, if the little arrows line up, the two objects attract each other with some force. \n\nThe forces that result from magnetic fields (and for that matter, electric fields) are fundamental forces, and part of the four fundamental forces of the universe (strong, weak, electromagnetic and gravity).  It is believed that these forces are caused, at their base, by particles passing "messenger particles" back and forth. In the case of electromagnetism, the messenger particle is a photon. How this actually works is still somewhat poorly understood, and is involved with the world of quantum mechanics, which is very counterintuitive but interesting. \n\nHowever, what is important is that we understand it well enough to make models of magnetism, and to make predictions based on those models which we can verify and use. All of electricity and electric motors are based on our ability to design systems with magnets and to be able to build and use them.
229163
In physics, a magnetic field is an entity produced by moving electric charges (electric currents) that exerts a force on other moving charges. (The quantum-mechanical spin of a particle produces magnetic fields and is acted on by them as though it were a current; this accounts for the fields produced by "permanent" ferromagnets.) A magnetic field is a vector field: it associates with every point in space a (pseudo-)vector that may vary in time. The direction of the field is the equilibrium direction of a compass needle placed in the field.