An experimental method for comparing the magnetic fields of an inner core and an outer core

Abstract

The application discloses an experimental method for comparing the magnetic fields of an inner core and an outer core. When a solenoid has an inner core and an outer core, which forms an electromagnet, a closed conductor loop is designed in the same plane at a certain distance below the inner core and the outer core. The magnetic field distribution of the inner core and the outer core is compared by comparing the induced current in the conductor loop. The new law beyond the Faraday's law of electromagnetic induction and the Lenz's law can be found by comparing the magnetic field distribution and the electromagnetic induction result. The magnetic field direction of the inner core and the outer core can be detected by the force of a small magnetic needle or a magnet. The above experimental method can be used to manufacture instruments for teaching and scientific research. The above experimental method can also be used to detect other magnetic field distributions similar to the inner core and the outer core.

Description

Technical Field

[0001] This invention relates to electromagnetic induction technology and electromagnet technology, and to comparing the distribution of magnetic fields of an inner iron core and an outer iron core by designing an electromagnetic induction circuit to compare the electromagnetic induction results. Background Technology

[0002] Whether it is electromagnetic induction technology or electromagnet technology, the outer iron core can play a certain role. Moreover, by comparing the magnetic field distribution characteristics of the inner and outer iron cores, physical laws can be further explored. This patent provides an experimental method for electromagnetic induction circuit to compare the magnetic fields of the inner and outer iron cores. By comparing the magnetic field distribution of the inner and outer iron cores, combined with the theory of induced electric field generated by changing current (see "Induced Electric Field Generated by Changing Current" [J]. Science and Technology Wind, 2019(02): 248) and "Electromagnetic Induction Law of Induced Electric Field Generated by Changing Current" [J]. Science and Technology Wind, 2020(18): 129), electromagnetic laws can be further revealed. The above experimental methods can also be used to make corresponding electromagnetic experimental teaching instruments and carry out further scientific research. Summary of the Invention

[0003] This invention provides an experimental method for comparing the magnetic field distributions of inner and outer iron cores. This method allows for the comparison of the differences in magnetic field distributions between the inner and outer iron cores. It also shows that when the same magnetic field direction passes through an induction circuit, the different magnetic field distributions can induce currents in opposite directions within the circuit. Applying this experimental method can further reveal electromagnetic laws and facilitate the fabrication of instruments for teaching and experimental research. The details are as follows:

[0004] A solenoid 1 is formed by tightly winding an insulating wire around the outside of an insulating cylinder. A cylindrical inner iron core 1 of the same height as the solenoid 1 is inserted into the solenoid 1, and a cylindrical outer iron core 1 of the same height as the solenoid is fitted around the outside of the solenoid. The inner iron core 1, the solenoid 1, and the outer iron core 1 together form an electromagnet 1. The electromagnet 1 can be placed vertically, and the magnetic fields at the same distance directly below the outer iron core 1 and the inner iron core 1 can be compared when the electromagnet 1 is energized. After a steady current is applied to the electromagnet 1, the direction of the magnetic field at the same distance from the bottom of the outer iron core 1 and the inner iron core 1 can be detected by a small magnetic needle or a magnet. By detecting the magnetic force of the small magnetic needle or magnet, it can be known that the direction of the magnetic field at the same distance from the bottom of the outer iron core 1 and the inner iron core 1 is the same. If the bottom of the outer iron core 1 attracts the N pole of the small magnetic needle, the bottom of the inner iron core 1 at the same distance will also attract the N pole of the small magnetic needle. If the bottom of the outer iron core 1 attracts the S pole of the small magnetic needle, the bottom of the inner iron core 1 at the same distance will also attract the S pole of the small magnetic needle. A closed conductor loop is designed near the bottom of the inner iron core 1 and the outer iron core 1 respectively. The magnetic field distribution of the inner iron core 1 and the outer iron core 1 is compared by comparing the induced current generated in the closed conductor loop, so as to find the relationship between the magnetic field distribution and the induced current. At a certain distance directly below the outer iron core 1, an insulated wire is wound around a small circle 1 with the same inner diameter as the outer iron core 1. The two ends of the insulated wire are folded outward at the point where the small circle 1 is about to close, and then the two ends extend outward in parallel with each other (the two segments of the wire extending outward in parallel with each other are parallel to one diameter of the small circle 1). When the circle formed by the outer diameter of the outer iron core 1 is projected at that distance, the two ends of the wire are folded in the opposite direction, and then wound around the projected circle to form a large circle 1. The two ends of the insulated wire are folded outward again at the point where the large circle 1 is about to close, and then the two ends extend outward in parallel with each other to a distance and then connect to an ammeter to form a closed conductor circuit 1. The large circle 1 and the small circle 1 are in the same plane and parallel to the bottom surface of the outer iron core 1. In this way, the area enclosed by the large circle 1 and the small circle 1 when they are wound around the outer iron core 1 to form a closed conductor circuit 1 is approximately equal to the area of ​​the bottom surface of the outer iron core 1. Draw a concentric small circle 2' inside the large circle 2' formed by the circular bottom edge of the inner iron core 1. On the plane where the conductor loop 1 is located directly below the inner iron core 1, referencing the closed conductor loop 1, use an insulated wire to wind a closed conductor loop 2. The winding method is as follows: On the plane where the conductor loop 1 is located, use an insulated wire to wind a small circle 2 (the small circle 2 is directly below the small circle 2') directly below the inner iron core 1 along the projection of the small circle 2'. At the point where the wound small circle 2 is about to close, fold the two ends of the insulated wire outwards, and then extend the two ends outwards in parallel (the two outwardly extending wire segments are parallel to one diameter of the small circle 2). After the projection of the large circle 2' formed by the bottom edge of the inner iron core 1 onto the plane of the conductor circuit 1, the two ends of the wire are bent in opposite directions, and then wound around the projection of the large circle 2' onto the plane to form a large circle 2. The wire with insulation is bent outward again at the point where the wound large circle 2 is about to close, and then the two ends are closely attached and extended outward in parallel to a distance to connect to the ammeter to form a closed conductor circuit 2. The conductor circuit 1 and conductor circuit 2 mentioned above are in the same plane and parallel to the bottom surface of the electromagnet 1. In this way, the area enclosed by the large circle 2 and the small circle 2 wound around the closed conductor circuit 2 near the bottom of the inner iron core 1 is approximately equal to the area between the large circle 2' and the small circle 2'. At the instant the current to the energized electromagnet 1 is disconnected, induced currents are generated in both closed conductor circuit 1 and closed conductor circuit 2. The directions of these induced currents are opposite, one clockwise and the other counterclockwise. This opposite direction is not because the magnetic field lines passing through closed conductor circuit 1 and closed conductor circuit 2 are in opposite directions when the electromagnet 1 is energized, but because the magnetic field distribution of the outer and inner iron cores 1 is different: the magnetic field near the bottom of the outer iron core 1 between the large circle 1 and the small circle 1 increases, while the magnetic field near the bottom of the inner iron core 1 between the large circle 2 and the small circle 2 decreases. The electromagnetic induction experiment using conductor circuits 1 and 2 demonstrates the difference in magnetic field distribution directly below the outer and inner iron cores 1. The applicable range of Faraday's law of electromagnetic induction combined with Lenz's law is actually the case where the magnetic field weakens from the outside to the inside (as in the case of the electromagnet 1 without the outer iron core 1). From the results obtained using the above experimental method, a conclusion can be derived: when the conductor and... The current that generates the magnetic field is parallel. When the current that generates the magnetic field changes, the conductor is equivalent to a power source. The induced electromotive force (EMF) generated by the conductor is proportional to the length of the conductor. The longer the conductor, the greater the rate of change of the current over time, and the closer the conductor is to the changing current, the greater the induced EMF generated in the conductor. (Approximately described using magnetic fields: When a conductor cuts magnetic lines of force in a magnetic field, and the magnetic field changes at the conductor, the longer the conductor and the greater the rate of change of the magnetic field strength at the conductor, the greater the induced EMF generated in the conductor.) The direction of the induced electric field is determined by the direction of the current that generates the magnetic field and the change in the strength of that current. There are three factors that determine the direction of the induced current in a closed conductor loop: in addition to the direction and strength of the changing current that generates the changing magnetic field, it is also related to the distribution of that changing current. (Approximately described using magnetic fields: There are three factors that determine the direction of the induced current in a closed conductor loop: in addition to the known reasons for the direction of the magnetic field and the change in the strength of the magnetic field, there is also the reason for the distribution of the magnetic field.) The electromagnetic induction experimental methods for winding closed conductor circuit 1 and closed conductor circuit 2 described above can also be used to compare the magnetic field distribution in other similar situations, and are not limited to the cases of inner iron core and outer iron core described above. The tools and materials such as iron cores and wires, as well as the shapes and relative positions of iron cores and conductor circuits, described in the above methods are only for illustrating the technology and not for limiting it. The above methods and techniques can be used to make corresponding instruments to facilitate teaching or scientific research. Attached Figure Description

[0005] The embodiments of the present invention will be further described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0006] Figure 1 This is a schematic diagram showing the direction of the magnetic field of the inner iron core 1 and the outer iron core 1 using a small magnetic needle and a bar magnet;

[0007] Figure 2 This is a schematic diagram comparing the magnetic field distribution of the inner and outer iron cores 1 when a closed conductor circuit is made directly below the outer and inner iron cores 1 of the electromagnet 1.

[0008] Figure 3 It is a schematic diagram that uses the current distribution as an analogy to the situation where there is both an inner iron core and an outer iron core, and then constructs a closed conductor circuit to compare the magnetic field distribution through the induced current generated.

[0009] Figure 4 An electromagnet is made of multiple layers of wire. The magnetic field of this electromagnet is compared with the magnetic fields of the outer and inner iron cores. Then, a closed conductor circuit is made to compare the magnetic field distribution through the phenomenon of electromagnetic induction. Detailed Implementation

[0010] To enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. Example 1

[0011] A solenoid 1 is formed by tightly winding an insulating wire around the outside of an insulating cylinder. A cylindrical inner iron core 1 of the same height as the solenoid 1 is inserted inside the solenoid 1, and a cylindrical outer iron core 1 of the same height as the solenoid is fitted around the outside of the solenoid. The inner iron core 1, the solenoid 1, and the outer iron core 1 together form an electromagnet 1. Figure 1 The left image below is a bottom view of electromagnet 1; the direction of the magnetic field near the outer iron core 1 and inner iron core 1 of electromagnet 1 is detected using a small magnetic needle and a bar magnet; like Figure 1 As shown, the top image from left to right is: an electromagnet with an inner iron core 1 inserted into an insulating cylinder with tightly wound wires at the same height as the cylinder; an outer iron core 1 at the same height as the solenoid; the bottom image from left to right is: a bottom view of the electromagnet 1; a side cross-section of the electromagnet 1, which includes the inner and outer iron cores 1, placed vertically, cut along its diameter; an illustration of the inner and outer iron cores 1 attracting small magnetic needles; and a magnetic force test diagram of the electromagnet 1 attracting a bar magnet. Using a small compass needle, the magnetic fields at the same distance directly below and near the outer iron core 1 and the inner iron core 1 are in the same direction. If the outer iron core 1 attracts the north pole (N) of the compass needle at a certain distance directly below it, then the inner iron core 1 at the same distance will also attract the N pole. Similarly, if the outer iron core 1 attracts the south pole (S) of the compass needle at a certain distance directly below it, then the inner iron core 1 at the same distance will also attract the south pole. Figure 1 The diagram on the right below shows the inner and outer iron cores 1 attracting the N pole of a small magnetic needle; I conducted the following experiment using a small magnetic needle, as follows: Figure 1 As shown in the left image above, the diameter of the inner iron core cylinder is 9.1 cm, and the diameter of the insulating cylinder is 9.2 cm; Figure 1 As shown in the right figure above, the inner diameter of the outer iron core 1 is 9.6 cm and the outer diameter is 10.8 cm; the height of both the inner and outer iron cores 1 is 4.35 cm; as... Figure 1 As shown in the right figure below, 0.3 cm directly below electromagnet 1, the outer iron core 1 attracts the N pole of the compass needle, and the inner iron core 1 also attracts the N pole of the compass needle. I used a bar magnet to detect the direction of the magnetic fields of the outer iron core 1 and the inner iron core 1. I conducted the following experiment: Figure 1 As shown in the right figure below, a bar magnet is tied to both ends of a 1 cm wide strap, forming a loop. The strap is placed on the tray of an electronic scale, and the bar magnet hangs vertically. The magnetic force of the inner iron core 1 and the outer iron core 1 on the bar magnet is observed separately. The experiment shows that when the electromagnet 1 is energized, the outer iron core 1 has an attractive force on the S pole of the bar magnet, and the inner iron core 1 also has an attractive force on the S pole of the bar magnet, while it will repel the opposite magnetic pole of the bar magnet. Figure 1 The right image below is a schematic diagram of the magnet attracted by the iron core 1 when energized. The distance between the S pole of the bar magnet and the electromagnet 1 is 0.25 cm. The experiment shows that the value displayed by the electronic scale is smaller when the circuit of electromagnet 1 is disconnected than the value when the circuit of electromagnet 1 is energized. The value is larger when electromagnet 1 is energized because the magnetic pole formed by the iron core 1 attracts the opposite magnetic pole of the S pole of the bar magnet when energized. Example 2

[0012] The electromagnetic induction circuit is designed to compare the magnetic fields of the inner iron core 1 and the outer iron core 1 by generating induced current. At a distance of 0.25 cm directly below the outer iron core 1 of the electromagnet 1, an insulated wire is wound into a small circle 1 with the same inner diameter as the outer iron core 1. The two ends of the insulated wire are folded outwards at the point where the small circle 1 is about to close, and then extended outwards parallel to each other (the two parallel outward-extending wire segments are parallel to one diameter of the small circle 1). When the wire reaches the projection circle formed by the outer diameter of the outer iron core 1 at that distance, the two ends of the wire are reversed and wound into a large circle 1 along the projection circle. The insulated wire is folded outwards again at the point where the large circle 1 is about to close, and then extended outwards parallel to each other until it connects to an ammeter to form a closed conductor circuit 1. A concentric circle is drawn inside the large circle 2' formed by the circular bottom edge of the inner iron core 1. Small circle 2' is formed by wrapping an insulated wire around a small circle 2 (the small circle 2 is directly below the small circle 2') on the plane of conductor circuit 1, directly below the inner iron core 1. The two ends of the insulated wire are folded outward at the point where the small circle 2 is about to close, and then the two ends are closely attached and extended outward in parallel (the two outwardly extended wire segments are parallel to one diameter of the small circle 2). After extending to the projection of the large circle 2' formed by the bottom edge of the inner iron core 1 on the plane of conductor circuit 1, the two ends of the wire are folded in the opposite direction, and then wrapped around the large circle 2' on the plane. The insulated wire is folded outward again at the point where the large circle 2 is about to close, and then the two ends are closely attached and extended outward in parallel to the distance to connect to the ammeter to form a closed conductor circuit 2. like Figure 2 As shown, the top diagram is a bottom view of electromagnet 1 (slightly enlarged for easier viewing); the middle diagram is a closed conductor circuit 1 formed by winding an insulated wire 0.25 cm directly below the outer iron core 1 when electromagnet 1 is placed vertically; the bottom diagram is a closed conductor circuit 2 formed by winding an insulated wire 0.25 cm directly below the inner iron core 1 when electromagnet 1 is placed vertically; circuits 1 and 2 are on the same plane; experiments show that at the instant the current to electromagnet 1 is disconnected, the induced currents generated in circuits 1 and 2 are in opposite directions; According to Faraday's law of electromagnetic induction and Lenz's law, the induced currents generated in loop 1 and loop 2 are in opposite directions. Therefore, when electromagnet 1 is energized, the magnetic field passing through loop 1 and the magnetic field passing through loop 2 are in opposite directions. However, this conclusion does not match the experimental results of the magnetic field direction in Example 1, which showed that the magnetic field directions are the same. There is another situation: when electromagnet 1 is energized, the magnetic field distribution within the area of ​​loop 1 and the magnetic field distribution within the area of ​​loop 2 are "exactly opposite"—the magnetic field within the area enclosed by loop 1 directly below electromagnet 1 gradually increases from the outside to the inside, while the magnetic field within the area enclosed by loop 2 gradually decreases from the outside to the inside. By comparing the magnetic fields near the inner iron core 1 and the outer iron core 1, it can be found that it is this "exactly opposite" that causes the induced currents generated in the two loops to be in different directions, rather than the magnetic fields passing through the two loops being in opposite directions. The above content can be understood as follows: Magnetism is the interaction between electric currents—currents in the same direction attract each other, and currents in opposite directions repel each other; the iron core near the current is attracted by the current because it is magnetized. Therefore, the magnetized iron core has "molecular current" generated inside it (using the terminology of Ampere's molecular current hypothesis); moreover, the direction of the molecular current generated inside the iron core after it is magnetized should be the same as the current that magnetized it, so that they can attract each other. Thus, when an insulated wire is tightly wound around the outer surface of a cylinder containing an inner cylindrical iron core 1, and an outer cylindrical iron core 1 is placed around the wire coil, a steady current is passed through the wire coil to form an electromagnet. After the cylindrical iron core 1 and the inner cylindrical iron core 1 are magnetized, the "molecular current" inside the cylindrical iron core 1 and the inner cylindrical iron core 1 should be in the same direction as the current in the wire coil. In this way, the "3 layers" of current can be regarded as concentric circles in the same direction. As for the cylindrical iron core 1 and the inner cylindrical iron core 1 themselves, the closer they are to the insulated wire coil wound on the cylinder, the stronger the magnetization and the larger the molecular current; the farther away they are, the weaker the magnetization and the smaller the molecular current. Because of the different strengths of magnetization (essentially, the different magnitudes of the molecular currents formed), the above "exactly opposite" occurs; the magnetic field within the area enclosed by loop 1 at a certain distance directly below the outer iron core 1 gradually increases from the outside to the inside, while the magnetic field within the area enclosed by loop 2 at the same distance directly below the inner iron core 1 gradually decreases from the outside to the inside. Therefore, loop 1 and loop 2 generate induced currents in opposite directions, rather than the magnetic fields passing through loop 1 and loop 2 having opposite directions. Example 3

[0013] By analogy with the situation where there is both an inner and an outer iron core, a closed conductor circuit is designed to compare the magnetic field distribution through an electromagnetic induction experiment. like Figure 3As shown in the left figure, seven identical straight currents a, b, c, d, e, f, and g are uniformly parallel and have the same current intensity, I. Rectangular conducting loops ABCD and ABEF are identical and symmetrical about AB in the same plane. The plane containing the two loops is parallel to the plane containing the seven currents, with the current plane on the inside. The projections of the seven straight currents onto the plane containing ABCD are symmetrical about the projection of current d. ABCD and ABEF are also symmetrical about the projection of current d. The projection of current a onto the plane containing ABCD is on the same straight line as side CD. Current g is on the same straight line as side AB. The projection of current d on plane CD is on the same straight line as EF. The projection of current d on plane ABCD is on the same straight line as AB. The ABCD loop and the ABEF loop share a side AB. When observing the induced current of the ABCD loop, side AF is disconnected. When observing the induced current of the ABEF loop, side AD is disconnected, as shown in the figure. The experiment shows that when all 7 currents are disconnected at the same time, the induced currents generated by the ABCD loop and the ABEF loop are equal in magnitude and opposite in direction. One is a clockwise induced current and the other is a counterclockwise induced current (similar to the opposite direction of the induced currents in loops 1 and 2 in Example 2). According to Lenz's law and Faraday's law of electromagnetic induction: if the induced currents generated by the two circuits are equal in magnitude, then the rate of change of magnetic flux through the two circuits is equal; if the induced currents generated by the two circuits are in opposite directions, then the magnetic fields through the two circuits are in opposite directions. But would the magnetic fields through two conductor circuits with seven currents of the same direction and magnitude that are symmetrical on the same side be in opposite directions? The magnetic field passing through the two loops is symmetrical about the projection of the current d—the magnetic field becomes stronger from CD to AB and from EF to AB. The induced currents generated in the two loops are in opposite directions, which conforms to the magnetic field distribution condition of "exactly opposite" mentioned in Example 2, and corresponds to the case of strong magnetic field in the middle and weak magnetic field on both sides in Example 2. Will the magnetic fields passing through ABCD and ABEF be in opposite directions? This can be analyzed using a magnetic experiment with a small compass needle or magnet, or through an electromagnetic induction experiment, as follows: Experiments show that when the current g is increased to a certain value while the other six currents remain unchanged, the induced currents generated by ABCD and ABEF can be in the same direction when the currents a, b, c, d, e, f, and g are simultaneously disconnected. Increasing the current g only changes the distribution of the magnetic field strength but does not change the direction of the magnetic field. Therefore, the reason for the different directions of the induced currents is due to the distribution of the magnetic field rather than the direction of the magnetic field. The direction of the induced current generated in the electromagnetic induction circuit is different due to the different strength of the magnetic field distribution. Thus, there are three reasons for the different directions of the induced current generated in the closed circuit: originally we only knew the reason for the direction of the magnetic field and the reason for the change in the strength of the magnetic field, but now we also know the reason for the distribution of the magnetic field. Let's analyze it below. Figure 3 The magnetic field distribution under the condition that the seven currents are of equal magnitude and uniformly distributed: The reason why induced currents can be generated in loops ABCD and ABEF is that the free electrons in the wires that make up the two loops are subjected to electromagnetic forces; and the force on the free electrons depends on the change of the magnetic field at their location and is unrelated to whether the conductors form a closed loop. Furthermore, the four sides AD, BC, AF, and BE do not contribute to the induced current in these two loops but only serve to conduct electricity (experimental proof below); the magnetic field strengths at the locations of sides AB and CD in the ABCD loop are different—side AB is closest to d, c and e are next closest, b and f are next next, and a and g are next next; while side CD is closest to a, b is next next, c is next next, d is next next, e is next next, f is next next next, and g is next next next. Thus, due to the distance from the current, the magnetic field at AB can be written as: strong + 2nd strong + 2nd second strong + 2nd second strong, and the magnetic field at CD can be written as: strong + second strong + second second strong + second second second strong + second second second second strong + second second second second second strong + second second second second second strong. Therefore, the magnetic field at the location of side AB is greater than that at C. The magnetic fields at the locations of sides D and EF are equal to those at the locations of sides CD and EF. Thus, when the currents a, b, c, d, e, f, and g are simultaneously de-energized and the magnetic field changes, the induced electromotive force (EMF) generated by AB is greater than that generated by CD and EF. Although the induced current in side AB is downward due to the EMF generated by AB, the induced current in side CD is downward due to the EMF generated by CD, and the induced current in side EF is downward due to the EMF generated by EF—although all are downward, the actual induced current directions in the two circuits are clockwise and counterclockwise respectively due to the difference in the magnitude of the induced EMF. The magnitude of the induced EMF generated by the conductor is proportional to the rate of change of the magnetic field strength at the location of the conductor over time. Further experimentation: Shorten side AB while keeping the length of side CD unchanged, such as... Figure 3As shown in the diagram on the right: To clearly see the conductors connecting the circuit, a cuboid is used. CD lies on one edge of the cuboid, and AB lies on another edge parallel to CD. The conductor AB starts from point B, goes to point B' (BB' lies parallel to a long edge of the cuboid), then from B' to point C' (C' lies at a vertex of the cuboid), then from C' to point C (CC' lies on a long edge of the cuboid), then from C to point D, then from D to point D' (DD' lies on a long edge of the cuboid), then from D' to A', and finally from A' to point A, forming a closed loop (AA' lies parallel to a long edge of the cuboid). The plane containing points A, B, C, and D, and the aforementioned current... The planes containing a, b, c, d, e, f, and g are parallel, while the planes containing A, B, C, and D are on the outside. The inward projections of AB and CD fall on currents d and a. As AB shortens, the induced current in the ABCD loop decreases until it reaches zero. After reaching zero, if side AB shortens further, a reverse induced current begins to be generated; the shorter side AB is, the larger the reverse induced current. Therefore, the reverse induced current in the ABCD loop is not due to a change in the direction of the magnetic field passing through the area of ​​the trapezoidal plane enclosed by ABCD, but rather because the induced electromotive force generated by the shortening of side AB decreases. When the lengths of sides AB and CD are equal, the induced current in the ABCD loop is equal to... Figure 3 The induced current generated in the ABCD circuit in the left figure (which also verifies) Figure 3 In the left figure ABCD circuit, AD and BC do not contribute to the generation of induced current but only play a conductive role; from the above, it can be seen that the induced electromotive force generated by side AB is proportional to the length of side AB. Example 4

[0014] An "electromagnet" is made by layering tightly wound solenoids according to their different inner diameters. By analogy between the outer and inner iron cores of this electromagnet, a closed conductor circuit is designed to compare the magnetic field distribution through electromagnetic induction. like Figure 4 As shown, the left side shows the largest of the five tightly wound solenoids. The five solenoids use the same wire specifications and have the same number of turns and the same winding method. The solenoids have the same height but different inner diameters. The five solenoids with tightly wound wires on their outer walls can be nested together in order of their inner diameters. The right side shows the bottom coil diagram when the five solenoids are nested together. The coils can be numbered 1, 2, 3, 4, and 5 from the outside to the inside. A current is passed through the interlocking solenoids to form an "electromagnet" without an iron core. The currents in wires 3, 2, and 1 decrease sequentially, and the currents in wires 3, 4, and 5 decrease sequentially. Two closed conductor loops are made on the plane near the bottom of this "electromagnet," similar to those in Example 2. The magnetic field distribution is compared through an electromagnetic induction experiment. The magnetic field is strongest at the projection of coil 3 on the plane near the bottom of the electromagnet, and the magnetic field on both sides decreases sequentially. This phenomenon can be compared with the case of having an inner iron core and an outer iron core in Example 2. The magnetic field distribution of inner and outer iron cores can be better understood from Example 4.

[0015] The above examples reveal electromagnetic induction phenomena beyond Faraday's law of electromagnetic induction, namely, the phenomenon that changes in the magnetic field outside the induction coil cause the induction coil to generate a larger induced current. The electromagnet 1 described above has both an outer iron core 1 and an inner iron core 1. The projection of the coil wound around the solenoid of electromagnet 1 onto the plane of the conductor circuit 1 directly below is a circle. Now, a closed conductor circuit 3 is wound around this circle. At the instant the current to the electromagnet 1, which is carrying a current I, is interrupted, an induced current will be generated in circuit 3. When there is an outer iron core 1, the induced current generated in circuit 3 is nearly twice as large as when there is no outer iron core 1. Analyzing this experimental phenomenon, the large induced current generated in circuit 3 is the result of the electromagnetic force generated at that location by the changing magnetic field on the free electrons in circuit 3. The changing magnetic field at the conductor of circuit 3 is determined by three parts of changing current: one is the change in the current carrying in the coil wound around the solenoid of electromagnet 1, one is the change in the current of the magnetized inner iron core 1 (hypothetically, there is a molecular current in it), and the other is the change in the current of the magnetized outer iron core 1 (hypothetically, there is a molecular current in it). Is the large induced current generated due to the increased magnetic flux through circuit 3? If there were no external iron core 1 to generate this large induced current, the coil of electromagnet 1 would need to carry a much larger current I'. However, the magnetic force at circuit 3 is much greater when electromagnet 1 without external iron core 1 and carrying a large current I' than when it has external iron core 1 and carrying a current I. This can be tested experimentally: place a circular iron plate with the same area as circuit 3 at the location of circuit 3 (the iron plate is 0.011 cm thick, has the same diameter as circuit 3, and is 0.25 cm away from the internal iron core 1). Electromagnet 1, without external iron core 1 but carrying a large current I', can attract this iron plate. When current I flows through the electromagnet, it cannot attract the iron piece; even when electromagnet 1 has an external iron core 1 and a current I flows through it, it still cannot attract the iron piece (the iron piece is directly below the internal iron core 1). This indicates that the magnetic flux through circuit 3 of electromagnet 1 without external iron core 1 and with a large current I is much greater than the magnetic flux through circuit 3 when current I flows through it with external iron core 1. This also indicates that the large induced current generated in circuit 3 at the instant the current to electromagnet 1 with external iron core 1 and with current I is cut off is not entirely due to the rate of change of magnetic flux through circuit 3. Experiments show that making the iron piece larger (with the thickness of the iron piece remaining constant) and the diameter of the larger iron piece equal to... The outer diameter of the outer iron core is used to determine the size of the large iron plate. When this large iron plate is placed directly below the outer iron core on the plane of circuit 3, electromagnet 1 can attract this large iron plate when a current I flows through the outer iron core 1 (but it cannot attract the circular iron plate with a diameter equal to the diameter of circuit 3 directly below the inner iron core 1). Even without a large current I' flowing through the outer iron core 1, electromagnet 1 can still attract this large iron plate directly below it. When the magnetic flux through circuit 3 is small (with current I flowing through electromagnet 1), the large induced current generated in circuit 3 at the instant the electromagnet 1 (with outer iron core 1) is de-energized can interact with the current flowing through the outer iron core 1. When the magnetic flux through the electromagnet 1 (without the external iron core 1) is large, the large induced current generated in the circuit 3 at the instant the electromagnet 1 is de-energized is equal to that generated in the circuit 3. This indicates that the large induced current generated in the circuit 3 when the external iron core 1 is present is not only due to the rate of change of the magnetic flux through the circuit 3, but also related to the change of the magnetic field outside the circuit 3. The change of the magnetic field outside the circuit 3 is due to the presence of the external iron core 1. Moreover, the experiment shows that when the electromagnet 1 is energized with current I, the magnetic field directly below the external iron core 1 and the magnetic field directly below the internal iron core 1 on the plane of the circuit 3 are in the same direction (as shown in the magnetic force experiment results of Example 1). In essence, Faraday's law of electromagnetic induction is an invention rather than a discovery: Faraday's law of electromagnetic induction describes the rate of change of magnetic flux through a coil, and only describes the relationship between the rate of change of magnetic flux through a coil and the induced electromotive force generated in the coil. However, when there is a change in the magnetic field outside the coil, there is obviously another situation. The phenomenon that the change in the magnetic field outside the coil causes the coil to generate an induced electromotive force is a supplement to the phenomenon of electromagnetic induction.

[0016] As can be seen from the above examples, when the direction of the induced current and the direction of the magnetic field are the same and the strength changes the same, in addition to Lenz's law, different directions of induced current can also be generated due to the different magnetic field distribution in the conductor circuit. Lenz's law states that the induced current has such a direction that the magnetic field generated by the induced current always opposes the change in the magnetic flux that caused the induced current; however, Examples 2 and 3 break this "opposition" rule, and "opposition" is not the essential reason that determines the direction of the induced current. The above electromagnetic induction phenomenon is attributed to the magnetization of the iron core. The idea that "magnetic flux passes through an iron core made of low magnetic resistance material, and the iron core (its function) is to reduce magnetic resistance and leakage flux, thus increasing inductance" actually deviates from the essence of the iron core's function. In Example 2, the inner iron core 1 and the outer iron core 1 are made of the same material. The magnetic fields passing through conductor circuit 1 and conductor circuit 2 are in the same direction, and both are generated at the moment when electromagnet 1 is de-energized, causing induced currents in the two circuits. The opposite directions of the generated induced currents are due to the different magnetization of the inner iron core 1 and the outer iron core 1, not because the magnetic resistance of the two iron cores is different or the reduction of leakage flux is different (it can be seen that the role of the iron core in the above electromagnetic induction phenomenon is due to magnetization, not because the iron core has low magnetic resistance or no leakage flux, etc.). The difference in the magnetization of the iron core in Example 2 is that the outer iron core 1 is an inner coil wound near electromagnet 1, while the inner iron core 1 is an outer coil wound near electromagnet 1.

[0017] The above are merely ordinary embodiments of the present invention and the technical principles used therein, and are not intended to limit the scope of the embodiments of the present invention. Any obvious modifications and applications made without departing from the essential spirit of the present invention will constitute an infringement of the patent right and will incur corresponding legal liability.

Claims

1. An experimental method for comparing the magnetic fields of an inner iron core and an outer iron core, characterized in that: A solenoid 1 is formed by tightly winding an insulating wire around the outside of an insulating cylinder. A cylindrical inner iron core 1 of the same height as the solenoid 1 is inserted into the solenoid 1, and a cylindrical outer iron core 1 of the same height as the solenoid is fitted around the outside of the solenoid. The inner iron core 1, the solenoid 1, and the outer iron core 1 together form an electromagnet 1. The electromagnet 1 can be placed vertically, and the magnetic fields at the same distance directly below the outer iron core 1 and the inner iron core 1 can be compared when the electromagnet 1 is energized. After a steady current is applied to the electromagnet 1, the direction of the magnetic field at the same distance from the bottom of the outer iron core 1 and the inner iron core 1 can be detected by a small magnetic needle or a magnet. By detecting the magnetic force of the small magnetic needle or magnet, it can be known that the direction of the magnetic field at the same distance from the bottom of the outer iron core 1 and the inner iron core 1 is the same. If the bottom of the outer iron core 1 attracts the N pole of the small magnetic needle, the bottom of the inner iron core 1 at the same distance will also attract the N pole of the small magnetic needle. If the bottom of the outer iron core 1 attracts the S pole of the small magnetic needle, the bottom of the inner iron core 1 at the same distance will also attract the S pole of the small magnetic needle. A closed conductor loop is designed near the bottom of the inner iron core 1 and the outer iron core 1 respectively. By comparing the induced current generated in the closed conductor loop, the magnetic field distribution of the inner iron core 1 and the outer iron core 1 is compared, so as to find the relationship between the magnetic field distribution and the induced current generated. At a certain distance directly below the outer iron core 1, an insulated wire is wound around a small circle 1 with the same inner diameter as the outer iron core 1. The two ends of the insulated wire are folded outward at the point where the small circle 1 is about to close, and then the two ends extend outward in parallel with each other (the two segments of the wire extending outward in parallel with each other are parallel to one diameter of the small circle 1). When the circle formed by the outer diameter of the outer iron core 1 is projected at that distance, the two ends of the wire are folded in the opposite direction, and then wound around the projected circle to form a large circle 1. The two ends of the insulated wire are folded outward again at the point where the large circle 1 is about to close, and then the two ends extend outward in parallel with each other to a distance and then connect to an ammeter to form a closed conductor circuit 1. The large circle 1 and the small circle 1 are in the same plane and parallel to the bottom surface of the outer iron core 1. In this way, the area enclosed by the large circle 1 and the small circle 1 when they are wound around the outer iron core 1 to form a closed conductor circuit 1 is approximately equal to the area of ​​the bottom surface of the outer iron core 1. Draw a concentric small circle 2' inside the large circle 2' formed by the circular bottom edge of the inner iron core 1. On the plane where the conductor loop 1 is located directly below the inner iron core 1, referencing the closed conductor loop 1, use an insulated wire to wind a closed conductor loop 2. The winding method is as follows: On the plane where the conductor loop 1 is located, use an insulated wire to wind a small circle 2 (the small circle 2 is directly below the small circle 2') directly below the inner iron core 1 along the projection of the small circle 2'. At the point where the wound small circle 2 is about to close, fold the two ends of the insulated wire outwards, and then extend the two ends outwards in parallel (the two outwardly extending wire segments are parallel to one diameter of the small circle 2). After the projection of the large circle 2' formed by the bottom edge of the inner iron core 1 onto the plane of the conductor circuit 1, the two ends of the wire are bent in opposite directions, and then wound around the projection of the large circle 2' onto the plane to form a large circle 2. The wire with insulation is bent outward again at the point where the wound large circle 2 is about to close, and then the two ends are closely attached and extended outward in parallel to a distance to connect to the ammeter to form a closed conductor circuit 2. The conductor circuit 1 and conductor circuit 2 mentioned above are in the same plane and parallel to the bottom surface of the electromagnet 1. In this way, the area enclosed by the large circle 2 and the small circle 2 wound around the closed conductor circuit 2 near the bottom of the inner iron core 1 is approximately equal to the area between the large circle 2' and the small circle 2'. At the instant the current to the energized electromagnet 1 is disconnected, induced currents are generated in both closed conductor circuit 1 and closed conductor circuit 2. The directions of these induced currents are opposite, one clockwise and the other counterclockwise. This opposite direction is not because the magnetic field lines passing through closed conductor circuit 1 and closed conductor circuit 2 are in opposite directions when the electromagnet 1 is energized, but because the magnetic field distribution of the outer and inner iron cores is different: the magnetic field near the bottom of the outer iron core 1 between the large circle 1 and the small circle 1 increases, while the magnetic field near the bottom of the inner iron core 1 between the large circle 2 and the small circle 2 decreases. The electromagnetic induction experiment using conductor circuits 1 and 2 demonstrates the difference in magnetic field distribution directly below the outer and inner iron cores. The applicable range of Faraday's law of electromagnetic induction combined with Lenz's law is actually the case where the magnetic field weakens from the outside to the inside (as in the case of the electromagnet 1 without the outer iron core 1). From the results obtained using the above experimental method, a conclusion can be derived: when the conductor and... The current that generates the magnetic field is parallel. When the current that generates the magnetic field changes, the conductor acts as a power source. The induced electromotive force (EMF) generated by the conductor is proportional to the length of the conductor. The longer the conductor, the greater the rate of change of the current over time, and the closer the conductor is to the changing current, the greater the induced EMF generated in the conductor. (Approximately described using magnetic fields: When a conductor cuts magnetic field lines in a magnetic field, and the magnetic field changes at the conductor, the longer the conductor and the greater the rate of change of the magnetic field strength at the conductor, the greater the induced EMF generated in the conductor.) The direction of the induced electric field is determined by the direction of the current that generates the magnetic field and the change in the strength of that current. There are three factors that determine the direction of the induced current in a closed conductor loop: in addition to the direction and strength of the changing current that generates the changing magnetic field, the distribution of that changing current is also relevant. (Approximately described using magnetic fields: There are three factors that determine the direction of the induced current in a closed conductor loop: in addition to the known reasons for the direction of the magnetic field and the change in the strength of the magnetic field, the distribution of the magnetic field is also relevant.) 2. The experimental method for comparing the magnetic fields of an inner iron core and an outer iron core according to claim 1, characterized in that: The electromagnetic induction experimental methods for winding closed conductor circuit 1 and closed conductor circuit 2 described above can also be used to compare the magnetic field distribution in other similar situations, and are not limited to the cases of inner iron core and outer iron core mentioned above.

3. The experimental method for comparing the magnetic fields of an inner iron core and an outer iron core according to claims 1 and 2, characterized in that: The tools and materials such as iron cores and wires, as well as the shapes and relative positions of iron cores and conductor circuits, described in the above methods are only for illustrating the technology and not for limiting it. The above methods and techniques can be used to make corresponding instruments to facilitate teaching or scientific research.

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