A magnetic flux invariance demonstrator

Abstract

The utility model discloses a magnetic flux invariance demonstrator, including equipment, a cylindrical magnet and a flexible wire frame, wherein the magnet is placed directly above the equipment, and the flexible wire frame is sleeved outside the equipment; the flexible wire frame is connected to an ammeter through a wire to form a passage, and the flexible wire frame is naturally placed on the outer surface of the equipment after crossing once; the equipment is composed of a bottom circular plate, a top circular plate and ten quadrilateral thin plates, and all the quadrilateral thin plates are arranged at equal angles between the top circular plate and the bottom circular plate, and the top end of the quadrilateral thin plate is connected to the top circular plate, and the bottom end is connected to the bottom circular plate; the quadrilateral thin plate is a right-angled trapezoidal structure, and the hypotenuse of the trapezoid is an inward concave arc. The utility model has a simple structure and low cost, improves the conditions for the generation of electromagnetic induction phenomenon, answers students' doubts, and fills the gap in experimental equipment.

Description

Technical Field

[0001] The utility model relates to the field of teaching equipment, in particular to a magnetic flux invariance demonstrator. Background Art

[0002] In high school physics textbooks, the mathematical expression of magnetic flux is: Φ=ΒS, where B is the magnetic induction intensity, whose magnitude corresponds to the density of magnetic flux lines, and S is the effective area of ​​the closed loop in the magnetic field.

[0003] Conditions for the occurrence of electromagnetic induction: "When the magnetic flux in a closed loop changes, an induced current is generated in the loop."

[0004] The textbook should summarize Faraday's law of electromagnetic induction through experiments: 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, E=△Φ / △t. Quantitative results are the core content of teaching and are what high school students must master. Before quantitative learning, qualitative knowledge and understanding are the foundation of students' thinking, the starting point for the construction of physical concepts, and also the difficulty.

[0005] Concept Construction:

[0006] Whether there is induced current depends on whether the magnetic flux changes.

[0007] That is: if △Φ≠0, there must be an induced current.

[0008] In class, students should be allowed to summarize the conditions for the generation of induced current through exploratory experiments.

[0009] Classroom experiment research ideas:

[0010] 1. S remains unchanged, B changes;

[0011] ① Changes in the relative position between the magnet and the wire frame, such as inserting or removing the magnet, or moving the wire frame closer or farther away from the magnet, will cause changes in the magnetic flux Φ in the fixed wire frame, thereby observing the induced current;

[0012] ② The current in the primary coil that generates the magnetic field changes. Keep the secondary coil connected to the ammeter to form a loop. The primary coil is connected to the power supply, switch, wire, resistor, and sliding rheostat to form a closed loop. When the switch is closed and energized, the magnetic field in the secondary coil changes from zero to one; when the switch is open, the magnetic field in the secondary coil changes from one to none; when the resistance of the sliding rheostat is adjusted, the strength of the magnetic field in the secondary coil changes, which will change the magnetic field B passing through the fixed wire frame (secondary coil), causing the magnetic flux in the secondary coil to change, thereby generating an induced current in the secondary coil.

[0013] 2. B remains unchanged, S changes.

[0014] ① Use force to change the shape of the wire frame. For example, if you stretch or squeeze the wire frame in a fixed magnetic field, the area of ​​the wire frame changes, the magnetic flux changes, and thus an induced current is generated;

[0015] ② The area and shape of the wire frame remain unchanged, and the magnetic field remains unchanged, but when the wire frame is rotated in the magnetic field, the number of magnetic lines of force passing through the plane of the wire frame changes, that is, the magnetic flux changes, thereby generating an induced current.

[0016] In the above experiments 1 and 2, one of B and S is kept unchanged, while the other one is changed, that is, one of the two elements of magnetic flux is changed. Therefore, the magnetic flux changes, that is, △Φ≠0, and an induced current will inevitably be generated.

[0017] These have relatively mature experiments and can be done in experiments in most schools.

[0018] Most students will think: Is there a situation where both B and S change but Φ remains unchanged?

[0019] The textbooks avoid this kind of situation because there is no corresponding and feasible experimental equipment. Summary of the invention

[0020] In view of the missing parts of the above-mentioned experiments, the purpose of the present utility model is to provide a magnetic flux invariance demonstrator, which fills the situation in which the magnetic field B and the wire frame area S change in the classroom experiment, but the magnetic flux Φ in the coil does not change.

[0021] In order to solve the above problems, the utility model adopts the following technical solutions:

[0022] The utility model provides a magnetic flux invariance demonstrator, characterized in that it comprises equipment, a cylindrical magnet and a flexible wire frame, wherein the magnet is placed directly above the equipment; the flexible wire frame is connected to an ammeter through a wire to form a passage, the flexible wire frame crosses once to form a closed area, and is placed on the outer surface of the equipment;

[0023] Furthermore, the soft wire frame is a multi-strand wire, the wire core is a copper wire, the outer sheath is an insulating material, and the two ends are respectively connected to red and black alligator clip wires, and the alligator clips can be connected to an ammeter.

[0024] Furthermore, the device is composed of a bottom circular plate, a top circular plate and ten quadrilateral thin plates, all of which are distributed at equal angles between the top circular plate and the bottom circular plate, and the top ends of the quadrilateral thin plates are connected to the top circular plate, and the bottom ends are connected to the bottom circular plate.

[0025] Furthermore, the quadrilateral thin plate is a right-angled trapezoidal structure, and the hypotenuse of the trapezoid is an inwardly concave arc.

[0026] The beneficial effects of the utility model are: the utility model has a simple structure and low cost, fills the blank of experimental equipment, improves all types of conditions for generating electromagnetic induction phenomena, answers students' doubts, and brings great convenience to teaching. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 A schematic diagram of the structure of a magnetic flux invariance demonstrator provided in Example 1 of the utility model;

[0029] Figure 2 A schematic structural diagram of a single quadrilateral thin plate of a magnetic flux invariance demonstrator provided in Example 1 of the utility model;

[0030] Figure 3 A schematic diagram of the distribution of the magnetic field around the cylindrical magnet provided in Example 1 of the utility model;

[0031] Figure 4 A schematic diagram of a reference shape for making a quadrilateral thin plate provided in Example 1 of the utility model;

[0032] Figure 5 A schematic diagram of the operation of a magnetic flux invariance demonstrator provided in Example 1 of the utility model;

[0033] Explanation of the accompanying reference numerals: 1. magnet; 2. flexible wire frame; 3. equipment; 4. ammeter; 5. hand-pulling direction. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments in the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model. Example 1

[0035] like Figure 1-2As shown, a magnetic flux invariance demonstrator comprises a device 3, a cylindrical magnet 1 and a flexible wire frame 2, wherein the magnet 1 is placed directly above the device 3, and the flexible wire frame 2 is sleeved outside the device 3; the flexible wire frame 2 is connected to an ammeter 4 through a wire to form a passage, and the flexible wire frame 2 is naturally placed outside the device 3 after crossing once;

[0036] The external shape of the device 3 is similar to the shape of the magnetic flux lines of the cylindrical magnet 1 used in the surrounding space;

[0037] The device 3 is composed of a bottom circular plate, a top circular plate and ten quadrilateral thin plates, all of which are distributed at equal angles between the top circular plate and the bottom circular plate, with the top ends of the quadrilateral thin plates connected to the top circular plate and the bottom ends connected to the bottom circular plate;

[0038] The quadrilateral thin plate is a right-angled trapezoidal structure, and the hypotenuse of the trapezoid is an inwardly concave arc.

[0039] Working principle:

[0040] The production process is as follows:

[0041] like Figure 3-4 As shown, the magnetic field is first selected, namely: a cylindrical magnet 1.

[0042] The second step is to measure the shape of the magnetic flux lines of the magnet 1 in the surrounding space, and use acrylic sheets (thickness of about 2 mm) to make thin plate-shaped equipment 3 according to the shape of the magnetic flux lines. Each sheet is a quadrilateral of the same shape, and there are a total of ten sheets.

[0043] The three sides of each quadrilateral thin plate are the three right-angled sides of a right-angled trapezoid, the lengths of the upper and lower bases are 1.8 cm and 10 cm, the height is 10.5 cm, and the fourth side is a curved side with a distance of 14 cm between the two end points. The shape of the curve is consistent with the shape of the magnetic flux lines of the cylindrical magnet 1 in this space.

[0044] The upper and lower bottoms of the equipment 3 are both circular sheets, and the upper and lower circular sheets can be made into double layers.

[0045] The diameter of the upper disc is 3.5 cm, and the diameter of the lower disc is 20 cm.

[0046] The top layer of the small disc above is the whole disc, and the bottom disc is cut along five diameters with equal spacing and 2 mm width. According to the radius, there are ten grooves in total. The two equal-sized discs are aligned and pasted together to form the upper base; the bottom layer of the large disc below is the whole large disc, and the top layer is cut along five diameters with equal spacing and 2 mm width. According to the radius, there are ten grooves in total. The two equal-sized discs are aligned and pasted together;

[0047] The ten cut rectangular thin plates are combined with the large and small round pieces as the upper and lower bases, plugged in along the 2 mm groove, and bonded as a whole to form device 3.

[0048] like Figure 5 As shown, the experimental implementation steps are as follows:

[0049] Connection Preparation

[0050] During the experiment, the large round surface of the device 3 is placed upright against the table, and the magnet 1 is placed on the small round piece above, facing and aligning. The outer side of the device 3 is covered with a flexible wire frame 2, and the flexible wire frame 2 is connected to the ammeter 4.

[0051] Φ change (test equipment 3)

[0052] When you hold the intersection of the wire frame with your hands, keep the area and shape of the wire frame unchanged, and move the wire frame up and down along the vertical axis, you will find that the pointer of the ammeter 4 deflects. Explanation: Because S does not change, but B changes, the magnetic flux Φ changes, so there is an induced current, which proves that there is no problem with equipment 3.

[0053] Φ does not change

[0054] ① Contraction

[0055] Keeping the above experimental connection, the wire frame is placed near the bottom of the equipment 3 and kept crossed.

[0056] Hold the two end points of the wire frame with both hands and pull it outwards with force. The wire frame is stressed, its area is reduced, and it moves upward along the outer curved surface of the equipment 3. At this time, it is observed that the pointer of the ammeter 4 does not move.

[0057] Explanation: When the wire frame moves upward, the area S decreases, and the magnetic induction intensity B at the location of the wire frame increases (the magnetic lines of force are denser), but the number of magnetic lines of force passing through the wire frame does not change, that is, the magnetic flux does not change, so there is no induced current.

[0058] Obviously, in this experimental example, both elements of the magnetic flux, B and S, have changed, but the magnetic flux passing through the closed loop has not changed, so no electromagnetic induction phenomenon will occur.

[0059] ② Expansion

[0060] Keeping the above experimental connection, the wire frame is placed near the top of the equipment 3 and kept crossed.

[0061] Hold the two end points of the wire frame with both hands, apply a little force to keep the wire frame still, and quickly move your hands closer. Due to the effect of gravity, the wire frame moves downward along the outer curved surface of the equipment 3. At this time, the area of ​​the wire frame increases, but the pointer of the ammeter 4 is still observed to be motionless.

[0062] Explanation: As the wire frame moves downward, the area S increases, and the magnetic induction intensity B at the location of the wire frame decreases (the magnetic lines of force are looser), but the number of magnetic lines of force passing through the wire frame does not change, that is, the magnetic flux does not change, so there is no induced current.

[0063] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A magnetic flux invariance demonstrator, characterized in that: It includes equipment, a cylindrical magnet and a flexible wire frame, wherein the magnet is placed directly above the equipment; the flexible wire frame is connected to an ammeter through a wire to form a passage, and the flexible wire frame crosses once to form a closed area, which is placed on the outer surface of the equipment.

2. A magnetic flux invariance demonstrator according to claim 1, characterized in that: The soft wire frame is a multi-strand wire, the wire core is a copper wire, the outer sheath is an insulating material, and the two ends are respectively connected to red and black alligator clip wires, and the alligator clips can be connected to an ammeter.

3. A magnetic flux invariance demonstrator according to claim 1, characterized in that: The device consists of a bottom circular plate, a top circular plate and ten quadrilateral thin plates, all of which are distributed at equal angles between the top circular plate and the bottom circular plate, the top ends of the quadrilateral thin plates are connected to the top circular plate, and the bottom ends are connected to the bottom circular plate.

4. A magnetic flux invariance demonstrator according to claim 3, characterized in that: The quadrilateral thin plate is a right-angled trapezoidal structure, and the hypotenuse of the trapezoid is an inwardly concave arc.

Images