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MAGNETIC MONOPOLE. A hypothetical elementary particle with a nonzero magnetic charge is a point source of a radial magnetic field. A magnetic charge is the source of a static magnetic field in exactly the same way that an electric charge is the source of a static electric field.

The laws of nature reveal a great degree of similarity between electric and magnetic fields. The field equations established by J. Maxwell, the same for both fields. There is, however, one big difference. Particles with electricity. charges, positive and negative, are constantly observed in nature, they create Coulomb electricity in the surrounding space. field. Magnetic charges, neither positive nor negative, have never been observed separately. A magnet always has two poles of equal magnitude at its two ends - positive and negative, and the magnetic field around it is the resulting field of both poles.

The laws of classical electrodynamics admit the existence of particles with one magnetic pole - magnetic monopoles and give them certain field equations and equations of motion. These laws do not contain any prohibitions, by virtue of which M.M. could not exist.

In quantum mechanics, the situation is somewhat different. Consistent equations of motion for a charged particle moving in the field of M. M., and for M. M. moving in the field of a particle, can be constructed only if the electric. the charge e of the particle and the magnetic charge n MM are related by the relation:

en = 1/2nhc, (*) where h is the Bar constant, c is the speed of light, and n is a positive or negative integer. This condition arises due to the fact that in quantum mechanics particles are represented by waves and interference effects appear in the motion of particles of one type under the influence of particles of another type. If M/ m with a magnetic charge n exists, then the formula (*) requires that all charged particles in its vicinity have a charge e equal to an integer multiple of the value hc/2n. I.e., electric. the charges must be quantized.

But it is the multiplicity of all observed charges to the electron charge that is one of the fundamental laws of nature. If M. M. existed, this law would have natures. explanation. There is no other explanation for the quantization of electricity. the charge is not known.

Assuming that e is the electron charge, the value of which is determined by the ratio e2/hc = 1/137, it is possible using the formula (*) to obtain the smallest magnetic charge along the monopole, determined by the equality po2/hc = 137/4. Thus, up to significantly more than E. It follows from this that the track of a fast-moving M.M. in a Wilson chamber or in a bubble chamber should stand out very much against the background of tracks of other particles. A thorough search for such tracks has been undertaken, but so far M. M. has not been found.

M. M. is a stable particle and cannot disappear until it meets another monopole having an equal in magnitude and opposite in sign magnetic charge. If m.m. are generated by high-energy cosmic rays continuously falling on the Earth, then they must occur everywhere on the Earth's surface. They were searched for, but also not found. The question remains whether this is due to the fact that M. M. are very rarely born, or whether they do not exist at all, P. A. M. Dirac.

From the editorial office. The hypothesis about the possibility of the existence of an M. M. particle having a positive or negative magnetic charge was expressed by P. A. M. Dirac (1931), therefore M. M. is also called the Dirac monopole.

MAGNETIC POLE, a section of the surface of a magnetized sample (magnet) on which the normal component of magnetization J is different from zero. If the magnetic flux in the sample and the surrounding space is graphically represented using magnetic field induction lines, then the magnetic field will correspond to the intersection of the sample surface with these lines (see Fig.). Usually the area of the surface from which the lines of force come out, naz. northern (N) or positive MP, and the section in which these lines are included is southern (S) or negative. The eponymous M. P. are repelled, the dissimilar ones are attracted. If we follow the analogy with the interaction of electricity. The surface density of magnetic charges bt = Jn, which is different from zero, can be attributed to M. P., although in reality there are no magnetic charges (see Magnetic Monopole). The absence of magnetic charges in nature leads to the fact that the lines of magnetic induction cannot be interrupted in the sample and in a magnetized sample, along with a magnetic field of one polarity, there must always be an equivalent magnetic field of the other polarity. For many technical purposes, magnets and electromagnets with a large number of m. p. pairs are used (for example, in electric. DC machines).

In the doctrine of terrestrial magnetism, M. P. is also considered (see Geomagnetic Poles and Magnetic Poles of the Earth). The arrow of the magnetic compass with its northern M. P. indicates the direction to the North pole of the Earth (more precisely, to the south M. P. of the Earth, which is located in the Northern hemisphere), the South pole - the direction to the South pole (north M. P. of the Earth).

Magnetic field and poles (N and S) of a magnetized steel rod. The lines with arrows indicate the lines of magnetic induction (the lines are closed in the space surrounding the rod).

MAGNETIC POTENTIOMETER, a device for measuring the difference of magnetic potentials between two points of a magnetic field or a magnetomotive force in a closed loop, which covers conductors with a current that creates a magnetic field. Magnetic potential is a conditional concept, because due to the closeness of the magnetic field lines (the absence of magnetic charges in nature) this field is not a potential one. However, with the technical. calculations and measurements often use the concept of the difference of magnetic potentials (magnetic voltage) Umag between two points of the field, defining Umag as the work of moving a single magnetic charge between selected points of the field.

M. P. is an induction coil (field coil). It has a flexible or rigid frame (usually flat with a constant cross-section along the length), on which a winding of a thin wire is uniformly wound (Fig.). The ends of the winding are attached to the meter, a ballistic galvanometer or a microwebermeter is usually used as a device for measurements in permanent magnetic fields, a voltmeter or an oscilloscope is used in alternating magnetic fields. If such M. P. If the magnetic field is in a constant magnetic field, and its ends are located at points with different magnetic potentials, then the magnetic flux penetrating the magnetic field - the flow coupling of the potentiometer - is proportional to the magnetic voltage between its ends (Umag). When the MP is removed from the field, its ends are closed or the field is turned off, the ballistic galvanometer needle is discarded, proportional to the change in the current coupling of F. The measured magnetic voltage Umag = F / k, where k is the constant M. P. According to the magnitude of Umag, the average strength of the magnetic field NSR between the ends of M is calculated. P.: Nsr = Umag/l, where l is the distance between the fixed points of the field. If the MP is closed, covering conductors with a current that creates a magnetic field, then the measured DF is proportional to the magnetomotive force.

Schematic representation of magnetic potentiometers with a field coil: a - rigid arc potentiometer, 6 - rectilinear potentiometer, b - potentiometer on a flexible frame (Rogovsky belt). B - lines of magnetic field induction.

Magnetic potential differences (magnetomotive force) can be measured starting from 10-3-10-2a (in the International System of Units, the magnetomotive force is measured in ampere turns or amperes).