An experimental method to reveal the origin of electromagnetic induction

Abstract

The invention discloses an experimental method for revealing the origin of electromagnetic induction. The specific method is as follows: a plurality of turns of a conductor 1 and a circle of an induced conductor are closely wound on a solid iron core 1 to form an electromagnetic induction device. When a direct current 1 in the conductor 1 is instantly changed to 0, an induced current 1 is generated in a closed loop of the induced conductor. When a cylindrical external iron core 2 is put on the conductor 1 wound around the iron core 1 and the induced conductor, a larger induced current 2 can be generated. Without the external iron core 2, when the large direct current 2 in the conductor 1 is instantly changed to 0, the induced conductor generates an induced current 2 in a closed loop. By comparing the magnetic force when the direct current 1 is passed through the conductor 1 without the external iron core and the conductor 1 with the external iron core and the conductor 1 without the external iron core, it can be known that the magnitude of the induced current generated in the conductor loop is not solely determined by the rate of change of the magnetic flux passing through the loop. The invention can produce tools for teaching experiments and will also drive the development of many technologies.

Description

Technical Field

[0001] The embodiments of the present invention relate to the field of electromagnetic induction, the field of electromagnets and the field of iron cores. Background Art

[0002] Faraday's law of electromagnetic induction states that the magnitude of the induced electromotive force in a closed loop is proportional to the rate of change of the magnetic flux passing through the loop. But does the magnitude of the induced electromotive force in a closed loop only relate to the change in the magnetic flux passing through the loop? Is it related to the change in the magnetic flux outside the loop? The present invention answers this question through an experimental method that reveals the origin of electromagnetic induction. Through the present invention, it can be known that the magnitude of the induced electromotive force in a closed loop is not only related to the change in the magnetic flux passing through the loop, but also to the change in the magnetic flux outside the loop; this method enriches the electromagnetic induction technology and expands the electromagnetic induction theory. This patented technical method is novel, easy to use, and has significant effects. It can be used vividly and effectively in classroom experiments. At the same time, this technology creatively displays the magnetic field level, which will surely drive the development of more electromagnetic technologies. Summary of the invention

[0003] This invention provides an experimental method to reveal the origin of electromagnetic induction, expands the electromagnetic induction theory, and enriches the electromagnetic induction technology. Its applications are as follows:

[0004] An electromagnetic induction device is formed by winding several turns of a conductor 1 and a circle of an induction conductor 2 on a cylindrical iron core 1. The conductor 1 and the power supply form a loop, and the induction conductor 2 and the ammeter form a loop. The conductor 1 and the induction conductor 2 can use the same specification of conductors. When the power supply is disconnected and the steady DC current 1 in the circuit of the conductor 1 instantly becomes 0, an induced current 1 will be generated in the closed loop of the induction conductor 2. A hollow cylindrical outer iron core 2 is sheathed outside the above-mentioned closely wound wire 1 and the iron core 1 wrapped with a circle of the induced wire 2 to form an electromagnetic induction device sheathed with an outer iron core. When the power supply is disconnected so that the steady DC current 1 in the wire 1 loop instantly becomes 0, an induced current 2 is generated in the closed loop of the induced wire 2, and the induced current 2 is larger than the above-mentioned induced current 1. Without the outer iron core 2, a large steady DC current 2 is passed through the conductor 1 of the electromagnetic induction device, so that the steady DC current 2 in the circuit of the conductor 1 instantly becomes 0 to form a new electromagnetic induction device, and an induced current 2 can be generated in the closed circuit of the induced conductor 2; The steady DC current 1 in the wire 1 of the electromagnetic induction device is kept unchanged to form an electromagnet 1, the steady DC current 1 in the wire 1 of the electromagnetic induction device with an outer iron core is kept unchanged to form an electromagnet 2, and the steady DC current 2 in the wire 1 of the new electromagnetic induction device is kept unchanged to form an electromagnet 3, and the above three iron cores are all placed vertically; The magnetic force of the three electromagnets mentioned above is analyzed by comparing and attracting rectangular narrow iron sheets, iron sheet 1 and iron sheet 2: the length of iron sheet 1 is the diameter length of the circular cross-section of the electromagnet formed by the cylindrical iron core 1 and the wound wire, and the length of iron sheet 2 is the length of the outer diameter of the external iron core 2; iron sheet 1 and iron sheet 2 are respectively at an equal distance below the above-mentioned electromagnet 1 or the above-mentioned electromagnet 2 or the above-mentioned electromagnet 3 - a corresponding distance 1; when iron sheet 1 or iron sheet 2 is placed horizontally at a corresponding distance 1 below electromagnet 1, the projection of the center of electromagnet 1 passes through the center of iron sheet 1 or the center of iron sheet 2, and electromagnet 1 cannot attract iron sheet 1 or iron sheet 2; when iron sheet 1 or iron sheet 2 is placed horizontally at a corresponding distance 1 below electromagnet 2, the center of the electromagnet The projection passes through the center of the iron sheet 1 or the center of the iron sheet 2. At this time, the electromagnet 2 cannot attract the iron sheet 1, but can attract the iron sheet 2. At this time, the iron sheet 1 is directly below the electromagnet in the external iron core 2 (the use of a cylinder for the iron core 1 described above is one of the convenient usages. Regardless of whether the iron core 1 is a cylinder or not, the iron sheet 1 should be directly below the corresponding electromagnet in this method - the iron sheet 1 must be exactly on the projection of the iron core 1 and the wound wire coil without exceeding it), and the iron sheet 2 is directly below the electromagnet and the external iron core 2 in the external iron core 2; when the iron sheet 1 or the iron sheet 2 is horizontally placed at a corresponding distance 1 directly below the electromagnet 3, the projection of the center of the electromagnet 3 passes through the center of the iron sheet 1 or the center of the iron sheet 2, and the electromagnet 3 can attract the iron sheet 1 and can attract the iron sheet 2;

[0005] The above-mentioned electromagnet 1 cannot attract the iron sheet 1 at a corresponding distance 1 directly below, which means that the magnetic field of the electromagnet is small, which means that the magnetic flux of the magnetic field of the electromagnet 1 passing through the loop of the induced wire 2 is small; the above-mentioned electromagnet 2 cannot attract the iron sheet 1 at a corresponding distance 1 directly below, which means that the magnetic field of the electromagnet in the iron core 2 outside the electromagnet 2 is small, which means that the magnetic flux of the magnetic field of the electromagnet 2 passing through the loop of the induced wire 2 is small, but the electromagnet 2 can attract the iron sheet 2 at a corresponding distance 1 directly below, which means that its overall magnetic field is large, and this larger overall magnetic field is the magnetic field of the electromagnet in the external iron core 2 plus the magnetic field of the external iron core. The iron sheet 2 is directly below them, so it is attracted; the electromagnet 3 can attract the iron sheet 1 and the iron sheet 2, which means that the magnetic field of the electromagnet 3 is large, which means that the magnetic flux of the magnetic field of the electromagnet 3 passing through the loop of the induced wire 2 is large; If the magnetic flux of the magnetic field of the electromagnet 3 passing through the loop of the induced wire 2 is large, then the corresponding magnetic flux change rate of the new electromagnetic induction device passing through the loop of the induced wire 2 is large; if the magnetic flux of the magnetic field of the electromagnet 2 passing through the loop of the induced wire 2 is small, then the corresponding magnetic flux change rate of the electromagnetic induction device with an iron core outside the sheath passing through the loop of the induced wire 2 is small; the large magnetic flux change rate of the new electromagnetic induction device passing through the loop of the induced wire 2 and the small magnetic flux change rate of the electromagnetic induction device with an iron core outside the sheath passing through the loop of the induced wire 2 can both cause the loop of the induced wire 2 to generate If an induced current 2 is generated, it means that the rate of change of the magnetic flux passing through the loop is not the only electromagnetic induction condition that determines the magnitude of the induced current generated by the loop; after the electromagnet 1 is covered with the external iron core 2, the electromagnet 2 is formed, and the overall magnetic field of the electromagnet 2 increases - the magnetic field outside the induced wire 2 increases, so it can attract the iron sheet 2 (it cannot attract the iron sheet 1), so the corresponding electromagnetic induction device with an external iron core can generate an induced current 2 because the change of the magnetic field outside the induced wire 2 increases, which means that the induced current generated in the loop is related to the change of the magnetic flux in the loop and the change of the magnetic flux outside the loop;

[0006] The iron core 1 around which the wire is wound and the external iron core 2 are made of iron material. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The following is a further description of the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the accompanying drawings described below are part of the embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying any creative work.

[0008] Figure 1 The schematic diagram is a schematic diagram of an iron core 1 and an external iron core 2 which are tightly wound with several turns of a conductor 1 and a circle of a sensed conductor 2.

[0009] Figure 2 The left figure is a schematic diagram of an electromagnetic induction device manufactured in an embodiment of the present invention, in which a conductor 1 is closely wound with several turns on an iron core 1, a variable current is generated in the conductor 1, and a sensing conductor 2 is wound around the bottom of the iron core 1, and two ends of the sensing conductor 2 are connected to a galvanometer to form a closed loop; Figure 2 The right figure is a schematic diagram of an electromagnetic induction device with an outer iron core when a hollow cylindrical outer iron core 2 is sheathed outside a conductor 1 that is tightly wound with several turns and a conductor 2 that is wound with one turn to be sensed;

[0010] Figure 3 Yes Figure 2 The two ends of the wire 1 are connected to a variable current and then connected to a steady DC current 1, thus becoming an electromagnet device. Figure 3This is a schematic diagram of using two uniform rectangular narrow iron sheets (the two narrow iron sheets are made of the same material, have the same width and thickness, and the only difference is that one of the iron sheets is short and is called iron sheet 1, and the other is long and is called iron sheet 2; the length of iron sheet 2 is the length of the outer diameter of the outer cylindrical iron core 2, and the length of iron sheet 1 is the length of the diameter of the circular cross section of the electromagnet formed by the cylindrical iron core 1 together with the wound wire) placed directly below the electromagnet without the outer iron core 2 and the electromagnet with the outer iron core 2 to detect the difference in the magnetic force of the electromagnet. The left figure shows that the iron sheet 1 is not attracted under the electromagnet without the outer iron core 2, and the right figure shows that the iron sheet 2 is attracted under the electromagnet with the outer iron core 2; DETAILED DESCRIPTION

[0011] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are partial embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative work belong to the protection scope of the present invention. Example Step 1

[0012] The cylindrical iron core 1 wound with the conductor 1 and the induction conductor 2 is 4.35 cm high, 9.10 cm in diameter, and weighs 2.263 kg. The external iron core 2 is 4.35 cm high, 10.8 cm in outer diameter, 9.6 cm in inner diameter, and weighs 670 g. The external iron core 2 is a cylindrical hollow iron core, such as Figure 1 As shown; the diameter of the conductor 1 and the sensed conductor 2 is 0.1 cm.

[0013] Specifically, an insulating wire 1 is tightly wound several turns on the outer surface of a cylindrical iron core 1, and the wire 1 and a steady DC power supply 1 form a loop; a sensed wire 2 with an insulating layer is wound around the bottom of the cylinder, and an ammeter (galvanometer) is connected to both ends of the wire 2 to form a closed loop; when the power supply 1 is disconnected, the steady DC current 1 in the wire 1 loop instantly becomes 0 - such as Figure 2 As shown in the left figure, an induced current 1 will be generated in the closed loop of the induced conductor 2; like Figure 2 As shown in the right figure, an external iron core 2 is put on the outside of the conductor 1 with several turns of the densely wound cylindrical iron core 1 and the induced conductor 2. At this time, the power supply 1 is disconnected so that the steady DC current 1 in the circuit of the conductor 1 instantly becomes 0, and another induced current 2 is generated in the circuit of the induced conductor 2; the induced current 2 is obviously larger than the induced current 1. For step 1 of the embodiment, I did the following application experiment: Experiment 1: After 38 turns of wire 1 were tightly wound on a cylindrical iron core 1 with a height of 4.35 cm, a cylindrical diameter of 9.10 cm, and a weight of 2.263 kg, the two ends of the wire 1 were connected to a No. 1 dry battery to form a loop, and the lower end of the iron core 1 was wrapped with a circle of induction wire 2, and the two ends of the wire 2 were connected to the galvanometer to form a closed loop, refer to Figure 2 In the left figure, when the dry battery lead 1 is disconnected, the maximum swing of the galvanometer pointer is 1 grid (galvanometer first gear); when the external iron core 2 (4.35 cm high, 9.6 cm inner diameter, 10.8 cm outer diameter, 670 g weight) is put on the outside of the iron core 1 wrapped with the wire, the maximum swing of the galvanometer pointer is 1.85 grids when the dry battery lead 1 is disconnected, which is 0.85 grids more than the maximum swing when the external iron core 2 is not put on; Example Step 2

[0014] like Figure 3 As shown, the variable current in the above-mentioned wire 1 is changed to a constant DC current 1 (the loop of the constant DC current power supply 1 is closed), thereby changing Figure 2 The electromagnetic induction device is an electromagnet device. At the same time, two uniform rectangular narrow iron sheets of different lengths, iron sheet 1 and iron sheet 2 (the two narrow iron sheets are made of the same material, have the same width and thickness, and the only difference is that iron sheet 2 is longer and iron sheet 1 is shorter; the length of iron sheet 2 is 10.8 cm of the outer diameter of the outer iron core 2, and the length of iron sheet 1 is 9.3 cm of the diameter of the circular cross section of the electromagnet formed by the cylindrical iron core 1 together with the wound wire) are placed horizontally directly below the electromagnet formed without the outer iron core 2 or with the outer iron core 2. The distance between the two iron sheets and the electromagnet is the same, and the center of the electromagnet is projected through the center of the iron sheet 2 or the center of the iron sheet 1 to test the difference in the magnetic attraction of the electromagnet on the iron sheet at this time. Figure 3 The left picture is a rough schematic diagram of the iron sheet 1 at 5 mm directly below the electromagnet without the outer iron core 2. Figure 3 The right picture is a rough schematic diagram of the iron sheet 2 being attracted 5 mm below the electromagnet of the outer iron core 2.

[0015] Specifically, if Figure 3 As shown in the left figure, the wire 1 is connected to the constant DC power supply 1 as shown in the figure to form a closed loop. At this time, the electromagnet without the external iron core 2 cannot attract the iron sheet 1 5 mm below it, and it cannot attract the iron sheet 2 5 mm directly below it (when the iron sheet 1 is used, the projection of the center of the electromagnet passes through the center of the iron sheet 1, and when the iron sheet 2 is used, the projection of the center of the electromagnet passes through the center of the iron sheet 2). Put the external iron core 2 on the outside of the electromagnet, as shown in the figure below. Figure 3As shown in the right figure, the wire 1 is connected to the constant DC power supply 1 to form a closed loop. At this time, the electromagnet of the outer iron core 2 can attract the iron sheet 2 5 mm below, but the iron sheet 1 5 mm below the electromagnet in the outer iron core cannot be attracted. For step 2 of the embodiment, I did the following application experiment: Experiment 2: Wire 1 is connected to a No. 1 dry battery to form a closed loop, and the induced wire 2 is connected to the galvanometer to form a closed loop; Iron sheet 1 is 9.30 cm long, 0.3 cm wide, and 0.011 cm thick; Iron sheet 2 is 10.8 cm long, 0.3 cm wide, and 0.011 cm thick; At this time, the electromagnet without the outer iron core 2 cannot attract the iron sheet 2 5 mm below, nor can it attract the iron sheet 1 5 mm below; Put the iron sheet 1 on the positive side of the electromagnet 2.5 mm below, the iron sheet 1 can be attracted; put an external iron core 2 on the outside of the electromagnet, at this time the electromagnet with the external iron core 2 can attract the iron sheet 2 5 mm below, but the iron sheet 1 5 mm below the electromagnet in the external iron core cannot be attracted. Put the iron sheet 1 2.5 mm below the electromagnet at this time, the iron sheet 1 can be attracted, and move the iron sheet 1 to one side along the strip direction of the iron sheet 1 so that a part of the iron sheet 1 is 5 mm below the external iron core 2, the iron sheet 1 can also be attracted. Example Step 3

[0016] Without the outer iron core 2, a large steady DC current 2 is passed through the wire 1. When the steady DC current 2 in the wire 1 instantly becomes 0, an induced current 2 can be generated in the circuit of the induced wire 2. In this way, a new electromagnet is formed when there is a steady DC current 2 in the wire 1. This new electromagnet can attract the iron sheet 1 5 mm directly below it, and can also attract the iron sheet 2 5 mm below it. For step three, do a specific experiment: Figure 2 The electromagnetic induction device in the left figure increases the steady DC current in wire 1 until the steady DC current is instantly 0 when the power is disconnected, and an induced current 2 can be generated in the induced wire 2; maintaining the increased steady DC current will become an electromagnet device, refer to Figure 3 The experiment on the attraction of iron sheet 1 and iron sheet 2 shows that it can not only attract iron sheet 1 5 mm below, but also attract iron sheet 2 5 mm below. The time used to disconnect the power supply in all steps of the above embodiment must be equal, so that the rate of change of the magnetic flux passing through the loop of the induced wire 2 can be compared; the way of disconnecting the power supply can also be changed to allow the steady DC current to change evenly to 0 within an equal time.

[0017] The above three steps in the embodiment achieve three things: 1. The outer iron core can generate a large induced current (induced current 2) in the induced wire loop 2; 2. Through the corresponding electromagnet device, it can be seen that after the outer iron core is put on, the magnetic flux passing through the loop of the induced wire 2 is still small - the outer iron core 2 does not increase the magnetic flux passing through the loop of the induced wire (it still cannot attract the iron sheet 1); 3. Increase the steady DC current in the conductor 1: The large steady DC current in the conductor 1 can generate an induced current 2 in the loop of the induced conductor 2 without the outer iron core. Then, it can be known from the correspondingly formed electromagnet device that the magnetic flux passing through the loop of the induced conductor 2 is large at this time. A conclusion can be drawn from the above embodiments: the induced current generated by (small rate of change of magnetic flux passing through the induced wire loop + external iron core) and the induced current generated by (large rate of change of magnetic flux passing through the induced wire loop + no external iron core) can be the same size. Specifically, the induced current generated by (small rate of change of magnetic flux inside the loop + large change of magnetic flux outside the loop) can be equal to the induced current generated by (large rate of change of magnetic flux inside the loop + small change of magnetic flux outside the loop). The experimental method of the above embodiments points out that the size of the induced current generated in the electromagnetic induction loop is not solely determined by the change of magnetic flux inside the loop, and the size of the induced current generated in the loop is related to the change of magnetic field inside the loop and also to the change of magnetic field outside the loop.

[0018] The above are only common embodiments of the present invention and the technical principles used, and do not limit the scope of the embodiments of the present invention. Any obvious changes and applications made without departing from the essential spirit of the present invention will constitute an infringement of this patent right and will bear corresponding legal responsibilities.

Claims

1. An experimental method for revealing the origin of electromagnetic induction, characterized in that: An electromagnetic induction device is formed by winding several turns of a conductor 1 and a circle of an induction conductor 2 on a cylindrical iron core 1. The conductor 1 and the power supply form a loop, and the induction conductor 2 and the ammeter form a loop. The conductor 1 and the induction conductor 2 can use the same specification of conductors. When the power supply is disconnected and the steady DC current 1 in the circuit of the conductor 1 instantly becomes 0, an induced current 1 will be generated in the closed loop of the induction conductor 2. A hollow cylindrical outer iron core 2 is sheathed outside the above-mentioned closely wound wire 1 and the iron core 1 wrapped with a circle of the induced wire 2 to form an electromagnetic induction device sheathed with an outer iron core. When the power supply is disconnected so that the steady DC current 1 in the wire 1 loop instantly becomes 0, an induced current 2 is generated in the closed loop of the induced wire 2, and the induced current 2 is larger than the above-mentioned induced current 1. Without the outer iron core 2, a large steady DC current 2 is passed through the conductor 1 of the electromagnetic induction device, so that the steady DC current 2 in the circuit of the conductor 1 is instantly changed to 0 to form a new electromagnetic induction device, and an induced current 2 can be generated in the closed circuit of the induced conductor 2; The steady DC current 1 in the wire 1 of the electromagnetic induction device is kept unchanged to form an electromagnet 1, the steady DC current 1 in the wire 1 of the electromagnetic induction device with an outer iron core is kept unchanged to form an electromagnet 2, and the steady DC current 2 in the wire 1 of the new electromagnetic induction device is kept unchanged to form an electromagnet 3, and the above three electromagnets are all placed vertically; The magnetic force of the three electromagnets mentioned above is analyzed by comparing and attracting rectangular narrow iron sheets, iron sheet 1 and iron sheet 2: the length of iron sheet 1 is the diameter length of the circular cross-section of the electromagnet formed by the cylindrical iron core 1 and the wound wire, and the length of iron sheet 2 is the length of the outer diameter of the external iron core 2; iron sheet 1 and iron sheet 2 are respectively at an equal distance below the above-mentioned electromagnet 1 or the above-mentioned electromagnet 2 or the above-mentioned electromagnet 3 - a corresponding distance 1; when iron sheet 1 or iron sheet 2 is placed horizontally at a corresponding distance 1 below electromagnet 1, the projection of the center of electromagnet 1 passes through the center of iron sheet 1 or the center of iron sheet 2, and electromagnet 1 cannot attract iron sheet 1 or iron sheet 2; when iron sheet 1 or iron sheet 2 is placed horizontally at a corresponding distance 1 below electromagnet 2, the center of the electromagnet The projection passes through the center of iron sheet 1 or the center of iron sheet 2. At this time, electromagnet 2 cannot attract iron sheet 1, but can attract iron sheet 2. At this time, iron sheet 1 is directly below the electromagnet inside the external iron core 2 (the use of a cylinder for iron core 1 as described above is one of the convenient uses. Regardless of whether iron core 1 is a cylinder or not, in this method, iron sheet 1 should be directly below the corresponding electromagnet - iron sheet 1 must be exactly on the projection of iron core 1 and the wound wire coil without exceeding it), and iron sheet 2 is directly below the electromagnet and the external iron core 2 inside the external iron core 2; when iron sheet 1 or iron sheet 2 is placed horizontally at a corresponding distance 1 directly below electromagnet 3, the projection of the center of electromagnet 3 passes through the center of iron sheet 1 or the center of iron sheet 2, and electromagnet 3 can attract iron sheet 1 and can attract iron sheet 2.

2. An experimental method for revealing the origin of electromagnetic induction according to claim 1, characterized in that: The above-mentioned electromagnet 1 cannot attract the iron sheet 1 at a corresponding distance 1 directly below, which means that the magnetic field of the electromagnet is small, which means that the magnetic flux of the magnetic field of the electromagnet 1 passing through the loop of the induced wire 2 is small; the above-mentioned electromagnet 2 cannot attract the iron sheet 1 at a corresponding distance 1 directly below, which means that the magnetic field of the electromagnet in the iron core 2 outside the electromagnet 2 is small, which means that the magnetic flux of the magnetic field of the electromagnet 2 passing through the loop of the induced wire 2 is small, but the electromagnet 2 can attract the iron sheet 2 at a corresponding distance 1 directly below, which means that its overall magnetic field is large, and this larger overall magnetic field is the magnetic field of the electromagnet in the external iron core 2 plus the magnetic field of the external iron core. The iron sheet 2 is directly below them, so it is attracted; the electromagnet 3 can attract the iron sheet 1 and the iron sheet 2, which means that the magnetic field of the electromagnet 3 is large, which means that the magnetic flux of the magnetic field of the electromagnet 3 passing through the loop of the induced wire 2 is large; If the magnetic flux of the magnetic field of the electromagnet 3 passing through the loop of the induced wire 2 is large, then the corresponding magnetic flux change rate of the new electromagnetic induction device passing through the loop of the induced wire 2 is large; if the magnetic flux of the magnetic field of the electromagnet 2 passing through the loop of the induced wire 2 is small, then the corresponding magnetic flux change rate of the electromagnetic induction device with an iron core outside the sheath passing through the loop of the induced wire 2 is small; the large magnetic flux change rate of the new electromagnetic induction device passing through the loop of the induced wire 2 and the small magnetic flux change rate of the electromagnetic induction device with an iron core outside the sheath passing through the loop of the induced wire 2 can both cause the loop of the induced wire 2 to generate If an induced current 2 is generated, it means that the rate of change of the magnetic flux passing through the loop is not the only electromagnetic induction condition that determines the size of the induced current generated in the loop; after the electromagnet 1 is put on the external iron core 2, the electromagnet 2 is formed, and the overall magnetic field of the electromagnet 2 is increased - the magnetic field outside the induced wire 2 is increased, so it can attract the iron sheet 2 (it cannot attract the iron sheet 1), so the corresponding electromagnetic induction device with an external iron core can generate an induced current 2 because the change of the magnetic field outside the induced wire 2 is increased, which means that the induced current generated in the loop is related to the change of the magnetic flux in the loop and also related to the change of the magnetic flux outside the loop.

3. An experimental method for revealing the origin of electromagnetic induction according to claims 1 and 2, characterized in that: The iron core 1 around which the wire is wound and the external iron core 2 are made of iron material.

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