The property that objects can attract iron, cobalt, nickel and other substances is called magnetism.Magnetism meansmagnetA characteristic that can attract paramagnetic matter is determined by the nature of the magnet itself.Magnetic force isInteraction forceThe magnet itself has no magnetic force, which is the result of the interaction between two magnetsrepulsionAnd gravity.
It can only be said that "the two poles of the magnet have the strongest magnetic force", not "the two poles of the magnet have the largest magnetic force".When it comes to the properties of magnets, we must say magnetism, and when it comes to the interaction between magnets, we should say magnetism.
Magnets and magnetic fields
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magnet
Magnet, as the name implies, refers to the object with magnetism, which can beMagnetic sourceIt can also be a magnetic conductor, such asFerriteAfter the two poles of the magnet are added with the iron plate, the magnetic field will concentrate on the edge of the iron plate.It has an invisible force, which can absorb some things and arrange some things.The force exerted by magnets to attract or repel objects is magnetic force.Since magnetic force is a force, it has magnitude, and the magnitude of magnetic force is closely related to the magnet itself.
Magnet scale capable of maintaining its magnetism for a long timepermanent magnet 。Such as natural magnetite (magnetite) and artificial magnet (aluminum nickel cobalt alloy).Also calledHard magnet。
If a straight metal wireThrough current, the space around the wire will produce a circlemagnetic field。wirewayMidstreamThe greater the overcurrent, the stronger the magnetic field generated.The magnetic field is rounded around the wire.The direction of the magnetic field can be determined according to“Right hand spiral rule”To determine: extend the thumb of the right hand, and bend the other four fingers together to the palm.At this time, the direction of thumb is the direction of current, and the direction of other four fingers is the direction of magnetic field[3]。In fact, the magnetic field generated by this straight wire is similar to the effect of placing a circle of small magnets with NS poles connected end to end around the wire[2]。
Right hand spiral rule
Solenoid electromagnetic field[2]
If a long metal wire is wound on a hollow cylinder in one direction, the object formed is calledsolenoid。Energize the solenoid. After the solenoid is energized, each turn of the solenoid will generate a magnetic field. The direction of the magnetic field is shown by the circular arrow.Then, at the position between two adjacent turns, the total magnetic field will cancel due to the opposite magnetic field direction;Inside and outside the solenoid, the magnetic fields generated by each turn of the coil are superimposed on each other to form a magnetic field shape.It can also be seen that the shape of the magnetic field outside the solenoid is the same as that generated by a magnet.The magnetic field inside the solenoid is just closed with the external magnetic fieldMagnetic line of force。The solenoid is represented as two rows of circles, which seems to cut the solenoid from the middle.There is a fork in the upper row, indicating that the current is fromFluorescent screenInternal outflow;There is a black dot in the lower row, indicating that the current flows from the outside to the inside of the fluorescent screen.[2]
3，flowLiquid metal。Cause of magnetic force, exceptPermanent magnetandElectrogenerated magnetismoutside.Scientists have found that flowing metal can produce a strong magnetic field. Some scientists have done experiments: pour molten iron into the sphere and make the sphere rotate, thus producing a huge magnetic force.It is speculated that there may be a liquid iron core in the earth and it is rotating constantly, thus forming a magnetic field.Also giveGeomagnetic fieldThe changes in strength and weakness, and even the changes in the history of the North and South Poles, have found the basis.
Simple definition: there is a magnetic field in the space where magnetic force can be generated.Magnetic field is a special material.There is a magnetic field around the magnet, and the changing electric field can also produce a magnetic field. The interaction between magnets is mediated by the magnetic field.
Magnetic line of forceThe closed magnet shows no magnetic field, and only the magnet with open magnetic line of force shows magnetic field.The magnetic field can be shielded by objects with magnetic conductivity, once the magnetic force line of the magnet isMagnetic conductorIt will occur after the shielding is closedMagnetic field weakening, or loss of magnetic force.
Current, moving charge, magnet or a special form of material in the space around the changing electric field.Since the magnetism of the magnet comes from the current, which is the movement of the charge, generally speaking, the magnetic field is generated by the moving charge or the changing electric field.
The basic feature of the magnetic field is that it can apply the moving chargeForce, the force of magnetic field on current, magnet ormoment of forceIt all comes from this.Modern theory shows that magnetic force isElectric field forceThe relativistic effect of.
Similar to the electric field, the magnetic field isSpace areawithinContinuous distributionOfVector field, the basic physical quantity describing the magnetic field isMagnetic inductionVector B can also be usedMagnetic induction line。However, as a vector field, the nature of magnetic field is quite different from that of electric field.The magnetic field generated by a moving charge or a changing electric field, or the total magnetic field of the sum of the two, is a passive rotational vector field. The magnetic lines of force are a closed family of curves that do not break or cross.In other words, there is no source that emits magnetic lines of force in the magnetic field, and there is no convergence of magnetic lines of forceEndThe closing of the magnetic line of force indicates that the loop integral along the magnetic line of force is zero, that is, the magnetic field is rotating rather thanpotential field（Conservative field）There is no scalar function like potential.
Magnetic induction: The number of magnetic force lines passing through the unit area perpendicular to the direction of magnetic force lines, also called the density of magnetic force lines, also calledMagnetic flux density, expressed in B, and the unit is T (tera).
Magnetic flux: magnetic flux is the total number of magnetic lines of force passing through a certain section area, expressed in Φ, and the unit isweber(Weber), the symbol is Wb.Magnetic flux passing through a coilexpressionIs: Φ=B · S (where B is the magnetic induction intensity and S is the area of the coil.)1Wb=1T·m2
Magnetic induction line: draw some curves in the magnetic field to make any point on the curvetangentThe direction is the same as that of the magnetic field at this point. These curves are called magnetic force lines.The magnetic line of force is a closed curve.It is specified that the direction of the north pole of the small magnetic needle is the direction of the magnetic force line.The magnetic force lines around the magnet all come out from the N pole to the S pole, and the magnetic force lines inside the magnet go from the S pole to the N pole.
The electromagnetic field isElectromagnetic actionThe medium and carrier of is a unified whole. Electric field and magnetic field are its two closely related and interdependent sides. Changing electric field generates magnetic field, changing magnetic field generates electric field, and changing electromagnetic field propagates in space in the form of wave.electromagnetic waveIt spreads at a limited speed, has exchangeable energy and momentum, the interaction between electromagnetic waves and objects, and the mutual transformation between electromagnetic waves and particles, all of which prove that electromagnetic fields areobjective existenceThe "special" of the substance is that it has noStatic mass。
