CN210223226U - Electromagnetic induction exploration experimental apparatus - Google Patents

Abstract

An electromagnetic induction exploration experimental device belongs to the technical field of teaching models and comprises a transformer, an ammeter, a small bulb, a rheostat, a low-voltage power supply, an alternating-current voltmeter and a switch; the transformer comprises a first coil, a second coil and a third coil; a first binding post and a second binding post are respectively arranged at two ends of the first coil; a third binding post and a fourth binding post are respectively arranged at two ends of the second coil; and a fifth binding post and a sixth binding post are respectively arranged at two ends of the third coil. The technical scheme quantitatively verifies the Faraday's law of electromagnetic induction by using a simpler device, can complete some experiments related to electromagnetic induction, and has good effect and low cost; the device further solves the problem of high school physics experiments, and better cultivates the physics experimental ability of students.

Description

Electromagnetic induction exploration experimental apparatus

Technical Field

The utility model belongs to the technical field of the model is used in the teaching, concretely relates to is an electromagnetic induction probes experimental apparatus.

Background

The Faraday's law of electromagnetic induction is an important law of physics of high school, but in practical teaching, the condition of middle school's laboratory is limited, and it is difficult to carry out quantitative verification, and the teacher can only combine physical history directly to introduce Faraday's law of electromagnetic induction, is unfavorable for student's understanding and grasp.

The experiment of self-inductance of cutting off the power supply, the experiment of exploring the relation between voltage and the number of turns at both ends of the transformer coil, the experiment of imitating the faraday, the experiment of demonstrating the blocking effect of inductance on alternating current and the like are all classic experiments of high school physics, and the experiment of "exploring the relation between voltage and the number of turns at both ends of the transformer coil" is arranged as student experiments by teaching materials.

However, in the practical teaching of schools, the experiments have problems, or the experiment effect is not good, or the experiments are not deep enough or comprehensive enough. The experiment of the student needing manual operation is similar to the experiment of the student in most mathematics schools, and the main reason is that the experiment result obtained by school equipment (transformers) is greatly different from the theoretical predicted value.

Therefore, it is necessary to modify the experimental scheme, so as to further solve the problem of physical experiments in high school and better train the physical experimental ability of students.

Disclosure of Invention

The utility model aims to overcome the defects mentioned above and provide an electromagnetic induction exploration tester.

The utility model discloses realize the technical scheme that its purpose adopted as follows.

An electromagnetic induction exploration tester comprises a transformer, an ammeter, a small bulb, a rheostat, a low-voltage power supply, an alternating-current voltmeter and a switch; the transformer comprises a first coil, a second coil and a third coil; a first binding post and a second binding post are respectively arranged at two ends of the first coil; a third binding post and a fourth binding post are respectively arranged at two ends of the second coil; a fifth binding post and a sixth binding post are respectively arranged at two ends of the third coil; the low-voltage power supply is an alternating current and direct current dual-purpose low-voltage power supply or a combination of an independent low-voltage alternating current power supply and an independent low-voltage direct current power supply.

The number of turns of the first coil, the second coil and the third coil is n respectively₁、n₂、n₃，n₁Greater than n₃Greater than n₂The resistance values of the three coils are not too different, and when one coil is selected to be connected with the ammeter in series to form a closed circuit each time, the total resistances of the three closed circuits are approximately equal, and the difference is not more than 20%.

The low-voltage power supply, the switch, the rheostat and a coil in the transformer are connected in series to form a closed circuit; the ammeter and the rest coil of the transformer are connected in series to form another closed circuit, and the low-voltage power supply is a low-voltage direct-current power supply.

And the first coil, the second coil or the third coil of the transformer is connected with the small bulb, the switch and the low-voltage power supply in series to form a closed circuit.

The small bulb is connected with a first coil, a second coil or a third coil of the transformer in parallel and then connected with a low-voltage power supply in series; the low voltage power supply is a low voltage dc power supply.

The small bulb is connected with the rheostat in series, then connected with the first coil, the second coil or the third coil of the transformer in parallel, and then connected with the low-voltage power supply in series, wherein the low-voltage power supply is a low-voltage direct-current power supply.

A coil of the transformer is connected with a low-voltage power supply; the small bulb is connected with the rest coil of the transformer in series; respectively measuring input voltage or output voltage between a first wiring terminal and a second wiring terminal of the transformer, between a third wiring terminal and a fourth wiring terminal of the transformer and between a fifth wiring terminal and a sixth wiring terminal of the transformer by using an alternating current voltmeter; the low voltage power supply is a low voltage ac power supply.

The technical scheme quantitatively verifies the Faraday's law of electromagnetic induction by using a simpler device, can complete some experiments related to electromagnetic induction, and has good effect and low cost; the device further solves the problem of high school physics experiments, and better cultivates the physics experimental ability of students.

Drawings

Fig. 1 is a schematic structural diagram of the present invention;

FIG. 2 is a schematic structural view of embodiment 1;

FIG. 3 is a schematic structural view of example 2;

FIG. 4 is a schematic structural view of embodiment 3;

FIG. 5 is a schematic structural view of example 4;

FIG. 6 is a schematic structural view of example 5;

in the figure: a rheostat (1), an ammeter (2), a small bulb (3), a transformer (4),

A first coil (4a), a first terminal (401), a second terminal (402),

A second coil (4b), a third terminal (403), a fourth terminal (404),

A third coil (4c), a fifth binding post (405), a sixth binding post (406),

Low voltage power supply (5), alternating current voltmeter (6), switch (7).

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

An electromagnetic induction exploration experimental device comprises a transformer (4), an ammeter (2), a small bulb (3), a rheostat (1), a low-voltage power supply (5), an alternating-current voltmeter (6) and a switch (7).

The transformer (4) comprises a first coil (4a), a second coil (4b) and a third coil (4 c); a first binding post (401) and a second binding post (402) are respectively arranged at two ends of the first coil (4 a); a third binding post (403) and a fourth binding post (404) are respectively arranged at two ends of the second coil (4 b); a fifth binding post (405) and a sixth binding post (406) are respectively arranged at two ends of the third coil (4 c); the low-voltage power supply (5) is an alternating current and direct current dual-purpose low-voltage power supply or a combination of an independent low-voltage alternating current power supply and an independent low-voltage direct current power supply.

The resistance values of the first coil (4a), the second coil (4b) and the third coil (4c) do not differ too much. When the Faraday's law of electromagnetic induction is quantitatively verified', a coil is selected to be connected in series with an ammeter to form a closed circuit each time, and a comparison experiment is carried out, so that the total resistance of the closed circuit in the comparison experiment is approximately equal, and the ratio of the maximum reading of the ammeter reflects the ratio of the maximum induced electromotive force. The three coil turns ratio is more flexible to set, and preferably, the turns ratio of the first coil (4a), the second coil (4b) and the third coil (4c) is 4:1: 2.

It should be noted that the first coil (4a), the second coil (4b) and the third coil (4c) are functionally distinguished, and may be separate entities or may share a part of the coil, and two terminals at corresponding positions may be combined into one.

The total resistance value of the rheostat (1) is 5-200 omega. Further, the varistor (1) comprises a sliding varistor or a potentiometer.

The ammeter (2) is a small-range ammeter, is a milliammeter or microammeter, has a resistance value of several ohms to several hundred ohms, and preferably, the range of the ammeter (2) is 15 mA.

The small bulb (3) comprises a small bulb and a 220V bulb. Preferably, the bulb with the small bulb specification of 6.3V, 0.15A or 2.5V, 0.3A, 220V is preferably a 3 watt LED bulb with 220V.

The alternating current voltmeter (6) can be a digital multimeter or a pointer multimeter.

Example 1 quantitative exploration of Faraday's law of electromagnetic induction

Purpose of the experiment: the Faraday's law of electromagnetic induction was explored quantitatively.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of the transformer (4) used in the experiment is respectively 4n, n and 2n, and the direct current resistance values of the three coils are not greatly different; the low-voltage power supply (5) uses 1 dry battery; the specification of the rheostat (1) is 20 omega and 2A; the measuring range of the ammeter (2) is 15 mA.

The experimental steps are as follows: firstly, connecting circuits according to a circuit diagram shown in fig. 2, wherein a low-voltage direct-current power supply (5), a switch (7), a rheostat (1) and a first coil (4a) of a transformer (4) are connected in series to form a closed circuit; the slide sheet of the rheostat (1) is arranged at a position with the resistance value close to the maximum, and the third coil (4c) of the transformer (4) is connected with the ammeter (2) in series to form a closed circuit.

Exploration suggestion 1: the slide of the varistor (1) is first placed in a position of maximum resistance, it being advisable to close the switch (7) or to open the switch (7) in the position of greater resistance. The ammeter is prevented from being damaged due to overlarge deflection angle of the pointer of the ammeter (2).

And secondly, closing the switch (7), rapidly moving the slide sheet of the rheostat (1) once, and slowly moving the slide sheet of the rheostat (1) once, and comparing which ammeter (2) has a larger reading. Then the slide sheet of the rheostat (1) is moved to a position with larger resistance value, and the switch (7) is turned off.

Third, the switch (7) is closed while the maximum reading (deflection grid number) of the ammeter (2) is observed and recorded.

And fourthly, opening the switch (7), and simultaneously observing and recording the maximum reading of the ammeter (2).

And fifthly, keeping the position of a slide sheet of the rheostat (1) unchanged, forming a series circuit by the ammeter (2) and a second coil (4b) of the transformer (4), closing a switch, and simultaneously observing the maximum reading (deflection lattice number) of the ammeter (2) and comparing the maximum reading of the ammeter (2) in the experimental operation of the step (3).

And sixthly, opening the switch (7), and observing the maximum reading of the ammeter (2) at the same time, and comparing the maximum reading of the ammeter (2) in the experimental operation of the step (4).

And seventhly, dismantling the circuit and arranging the equipment.

Exploration suggestion 2: because the resistance values of the second coil (4b) and the third coil (4c) are not greatly different, after the second coil and the third coil are respectively combined with the ammeter (2) to form a series circuit, the direct current resistance values of the closed circuit in a plurality of experimental operations can be considered to be approximately equal.

And (4) experimental conclusion: 1. in the second experimental operation, when the slide sheet of the rheostat (1) is moved rapidly, the reading of the ammeter (2) is larger. Indicating that the faster the magnetic flux changes through the closed loop, the greater the induced electromotive force generated.

2. Compared with the experiment operation in the fifth step, the direct current resistance value of the closed circuit is approximately equal, the magnetic flux change rate passing through the closed circuit is approximately equal, and the turn ratio of the third coil (4c) to the second coil (4b) is 2: 1, the maximum reading of the ammeter (2) is approximately 2 times of that of the latter, which shows that the magnitude of induced electromotive force is proportional to the number of turns of the coil.

3. And comparing the fourth step with the sixth step, wherein when the switch is disconnected, the maximum reading of the ammeter in the former step is approximately 2 times that of the ammeter in the latter step, and the magnitude of the induced electromotive force is in direct proportion to the number of turns of the coil.

According to faraday's law of electromagnetic induction: the magnitude of the induced electromotive force in the closed circuit is proportional to the rate of change of the magnetic flux through the circuit. If the international system of units is adopted, the closed circuit is a coil with n turns, and the expression of Faraday's law of electromagnetic induction is：

The correctness of the Faraday's law of electromagnetic induction is quantitatively tested by the above experimental results.

The experimental method of this embodiment may also be slightly changed, for example, the low voltage dc power supply (5), the switch (7), the varistor (1), and the second coil (4b) of the transformer (4) are connected in series to form a closed circuit; the ammeter (2) is firstly connected with a third coil (4c) of the transformer (4) in series to form a closed circuit. In the fifth step, the ammeter (2) and the first coil (4a) of the transformer (4) form a series circuit.

Example 2 investigation of the blocking effect of an inductor on an alternating current

Purpose of the experiment: the effect of the inductor on the resistance of the alternating current is known, which means that the self-inductance of the coil used in this experiment is larger or smaller.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of the transformer (4) used in the experiment is respectively 4n, n and 2n, and the direct current resistance values of the three coils are not greatly different; the low-voltage power supply (5) is an AC/DC low-voltage power supply; the specification of the small bulb (3) is 6.3V and 0.15A; the range of the alternating current voltmeter (6) is 20V.

The experimental steps are as follows: firstly, a circuit is connected according to a circuit diagram of fig. 3, a first coil (4a) of 4n turns of a transformer (4) is connected with a small bulb (3) and a closed switch (7) in series and then is connected to a low-voltage power supply (5), and the low-voltage power supply (5) selects a direct current 6V gear.

And secondly, closing the switch (7) and observing the light emitting condition of the small bulb (3).

And thirdly, the switch is disconnected, the low-voltage power supply (5) is switched to an alternating current 6V gear, the switch is closed again, and the light emitting condition of the small bulb (3) is observed.

Exploration suggestion 1: when the power supply is changed to an AC 6V power supply, the small bulb (3) is observed whether the brightness changes slightly or not at all.

Fourthly, the alternating current 20V gear is selected in the measuring range of the alternating current voltmeter (6). Two meter pens are contacted with the wiring terminals at the two ends of the small bulb (3), and the reading of the alternating voltage meter (6) is observed.

And fifthly, replacing the coil with a third coil (4c) with 2n turns, and repeating the steps (1) to (4).

And sixthly, replacing the coil with a second coil (4b) with n turns, and repeating the steps (1) to (4).

And seventhly, pulling out the plug, dismantling the circuit and arranging the equipment.

Exploration suggestion 2: the choke coils in the electrical and electronic technologies are classified into two types, one type is a low-frequency choke coil, the coil is wound on an iron core, the number of turns is large, the blocking effect on alternating current is large, and the characteristics are summarized as direct current passing and alternating current blocking; the other type is a high-frequency choke coil, the coil is wound on a ferrite core or is hollow, the number of turns is small, the self-inductance is small, and the characteristics are summarized as direct current passing, low frequency passing and high frequency blocking. The coils in the transformer can be classified into which type of choke coil according to the characteristics of the coils shown in the experiment.

Experimental phenomena: in a certain experiment, in the second step of operation, the small bulb (3) connected in series with the coil (4a) has high luminous brightness. In a third step, the small bulb (3) connected in series with the coil (4a) does not emit light. In the fourth step the ac voltage representative number is close to zero. In the fifth step, the filament of the small bulb (3) turns red, no light is seen, and the voltage representation number is about 0.79V. In the sixth step, the small bulb (3) emits light, but the brightness is darker, and the voltage at two ends is measured to be about 3.32V.

And (4) experimental conclusion: the above experimental phenomena illustrate that the inductor coil has a blocking effect on the alternating current. According to the characteristics of three coils in the transformer (4) shown in the experiment. The number of turns of the first coil (4a) with 4n turns is the largest, the wire diameter is also thick, the self-inductance coefficient is large, the first coil plays a role in passing direct current and blocking alternating current in the experiment, and the first coil can be considered as a low-frequency choke coil. The second coil (4b) with n turns has the least number of turns, the wire diameter is thinner, the self-inductance coefficient is smaller, the low-frequency alternating current can be allowed to pass through the coil, but the effect of obstruction is also achieved (the brightness of the bulb A is darker), and the high-frequency choke coil can be considered as a high-frequency choke coil. The third coil (4c) of 2n turns exhibits a characteristic in between.

Example 3 investigation of the self-inductance phenomenon upon power failure: the small bulb twinkles once

Purpose of the experiment: the phenomenon of self-inductance of power failure is understood and explained, while the self-inductance coefficient of the coil is recognized to be related to the size, shape, number of turns, etc. of the coil.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of the transformer (4) used in the experiment is respectively 4n, n and 2n, and the direct current resistance values of the three coils are not greatly different; the low-voltage power supply (5) is a battery pack formed by connecting 2 dry batteries in series; the specification of the small bulb (3) is 6.3V and 0.15A (or a 220V 3W LED bulb).

The experimental steps are as follows: firstly, a small bulb (3) is connected with a first coil (4a) of a transformer (4) in parallel and then connected with a low-voltage power supply (5) in series, and a circuit is connected according to a circuit diagram shown in fig. 4.

And secondly, closing the switch and observing the brightness of the small bulb (3).

And thirdly, turning off the switch and observing the light emitting condition of the small bulb (3) at the moment of turning off.

And fourthly, replacing the coil with a third coil (4c) of the transformer (4) and repeating the experiment.

And fifthly, replacing the coil with a second coil (4b) of the transformer (4) and repeating the experiment.

And sixthly, dismantling the circuit and arranging the equipment.

And (4) safety prompting: the energization time of the coil of the transformer (4) is not too long so as to avoid damaging the transformer (4).

The exploration and prompt are as follows: please explain the experimental phenomenon and think according to the learned knowledge, in order to observe that the small bulb (3) is turned on and off at the moment of the switch (7) being turned off, what requirements are required for the resistance values of the two branches.

Experimental phenomena: in the third step of operation, the switch (7) is switched off instantly, the small bulb (3) is seen to flash and then is extinguished, and the phenomenon is very clear. In the fourth step of operation, the small bulb (3) is turned off after being slightly lightened at the moment that the switch (7) is turned off. In the fifth step of operation, at the moment that the switch (7) is switched off, the small bulb (3) cannot be observed to flash and then extinguish, and the obvious delayed extinguishing effect is not generated.

And (4) experimental conclusion: 1. at the moment when the switch (7) is switched off, the coil generates self-induced electromotive force to prevent the current from decreasing, the coil plays a role of a power supply, at the moment, the current value in the small bulb (3) is gradually reduced from the normal current value of the coil, but in order to see that the small bulb (3) is brighter and then is extinguished, the current passing through the coil before the switch (7) is switched off is required to be much larger than the current of the small bulb (3) (namely the resistance value of the coil is much smaller than the resistance value of the small bulb (3)).

2. In the fourth and fifth steps of operation, the effect is not obvious once the small bulb (3) is flashed, in the third experiment, before the switch (7) is switched off, the resistance values of the three coils are not greatly different, the normal current values of the coils are not greatly different, and after the switch (7) is switched off, the loop resistance is not greatly different mainly because the self-inductance coefficients of the three coils are different (the self-inductance functions are different), the thicker the coil is, the more the number of turns is, and the larger the self-inductance coefficient is due to the addition of the iron core. The number of turns of the first coil (4a) with 4n turns is large, the diameter of the multi-wire is large, the self-inductance coefficient is large, and the experimental effect is good. And the number of turns of the second coil (4b) with n turns is small, the wire diameter is small, the self-inductance coefficient is minimum, and the experimental effect is the worst.

Example 4 investigation of factors affecting the self-inductance effect of power-off

Purpose of the experiment: understanding and explaining the self-induction phenomenon of power failure, and simultaneously exploring the factors influencing the experimental effect.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of the transformer (4) used in the experiment is respectively 4n, n and 2n, and the direct current resistance values of the three coils are not greatly different; the low-voltage power supply (5) is a battery pack formed by connecting 2 dry batteries in series; the total resistance value of the rheostat (1) is 20 omega; the specification of the small bulb (3) is 2.5V and 0.3A.

The experimental steps are as follows: first, in the circuit diagram shown in fig. 5, the varistor (1) is not connected, and the small bulb (3) is directly connected in parallel with the first coil (4a) of the transformer (4) and then connected in series with the low-voltage power supply (5) to connect the circuit.

And secondly, closing the switch (7) and observing the brightness of the small bulb (3).

And thirdly, turning off the switch (7) and observing the light emitting condition of the small bulb (3) at the moment of turning off.

Fourthly, the small bulb (3) is connected with the rheostat (1) in series, the circuit is connected according to the circuit diagram of figure 5, and the slide sheet of the rheostat (1) is arranged at the position where the resistance value is close to the maximum value. And closing the switch (7) and moving the slide sheet of the rheostat (1) to ensure that the small bulb (3) has darker brightness.

And fifthly, turning off the switch (7) and observing the light emitting condition of the small bulb (3) at the moment of turning off. The switch (7) is opened again after the switch is closed again, and the observation can be carried out for a plurality of times.

And sixthly, replacing the coil with a third coil (4c) with 2n turns, and repeating the experimental operations of the steps (4) and (5).

And step seven, replacing the coil with a second coil (4b) with n turns, and repeating the experimental operations of the steps (4) and (5).

And eighthly, dismantling the circuit and arranging the equipment.

And (4) safety prompting: the coil of the transformer (4) is not energized for too long a time to avoid damaging the transformer (4).

The exploration and prompt are as follows: please explain the experimental phenomenon and compare it with the experimental effect of the previous experiment.

Experimental phenomena: and in the third step, the sixth step and the seventh step, the small bulb is not obviously observed to be brighter and then extinguished at the moment of the switch disconnection. In the fifth step, the small bulb can be seen to be brighter and then extinguished at the moment when the switch is turned off.

And (4) experimental conclusion: 1. the small bulb (3) is connected with the rheostat (1) in series, so that when the small bulb (3) is darker in brightness, the resistance value of the coil is far smaller than the total resistance value of the small bulb (3) and the rheostat (1), and the current passing through the coil before the switch is disconnected is far larger than that of the small bulb (3). Thus, when the switch is turned off, the current in the small bulb (3) is gradually reduced from the normal current value of the coil, and the current value is still larger than the bulb current value when the switch is turned off for a longer time, so that in the fifth step of operation, the small bulb (3) can be seen to be brighter and then turned off. However, in the third step of operation, although the resistance of the coil is smaller than that of the bulb, the resistance is not much smaller, so that the current passing through the coil before the switch is turned off is not much larger than that of the small bulb (3), and the effect that the small bulb (3) is brighter when the switch is turned off is not obvious. The first condition for the small bulb (3) to be brighter is therefore: the current through the coil before the switch is opened is much greater than the current of the small bulb (3).

In the sixth step and the seventh step, although the first condition is met, the twinkling effect of the small bulb (3) is not obvious, mainly because the self-inductance coefficients of the three coils are different. The self-inductance coefficient of the 4 n-turn thick coil is large, and the experimental effect is good. And the thin coil with n turns has the smallest self-inductance coefficient and the worst experimental effect. The second condition for the small bulb to be brighter is therefore: the self-inductance of the coil is sufficiently large.

In comparison with example 3, when the switch is closed, both lamps have darker brightness and the current is less than the respective rated current. However, the rated current of the 2.5V small bulb (3) is 0.3A, and the rated current of the 6.3V small bulb (3) is only 0.15A although the rated voltage is high. At the moment of switch off, the current value in the small bulb is gradually reduced from the normal current value of the coil, but the current passing through the 6.3V small bulb (3) is kept above the rated current value for a longer time, so the effect of flashing the 6.3V small bulb is better.

Example 5 investigation of the voltage across a transformer coil in the case of a power supply

Purpose of the experiment: through the research, the transformer ratio formula is further realized to be only suitable for an ideal transformer, and the actual voltage of the secondary coil of the transformer is reduced due to loss during power supply.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of the transformer (4) used in the experiment is respectively 4n, n and 2n, and the direct current resistance values of the three coils are not greatly different; the low-voltage power supply (5) is an alternating-current low-voltage power supply; the specification of the small bulb (3) is 6.3V and 0.15A; the range of the alternating current voltmeter (6) is 20V.

The experimental steps are as follows: in the first step, a third coil (4c) of 2n turns of a transformer (4) is connected with an alternating current and direct current dual-purpose low-voltage power supply (5) by a lead (an alternating current 4V gear is selected).

Secondly, switching on a power supply, measuring and recording input voltage between a fifth binding post (405) and a sixth binding post (406) of the transformer (4), output voltage between a first binding post (401) and a second binding post (402) and output voltage between a third binding post (403) and a fourth binding post (404) by using an alternating voltage meter (6), and analyzing whether experimental data meet a transformation ratio formula of an ideal transformer or not

And thirdly, disconnecting the power supply, and connecting the circuit according to the circuit diagram of fig. 6, namely connecting a third coil (4c) with 2n turns with an alternating-current low-voltage power supply (5), supplying power to the small bulb (3) by using a first coil (4a) with 4n turns, and idling the second coil (4b) with n turns.

And fourthly, switching on the power supply, and observing the light emitting condition of the small bulb (3). And then, measuring the input voltage between a fifth binding post (405) and a sixth binding post (406) of the transformer (4) by using an alternating current voltmeter (6), measuring the output voltage between the first binding post (401) and the second binding post (402) (namely the voltage at two ends of the small bulb (3)), and measuring and recording the output voltage between the third binding post (403) and the fourth binding post (404).

Exploration suggestion 1: after the input voltage of the transformer (4) is measured, the voltage at two secondary windings of the transformer can be predicted to be larger than the maximum value, and the actual output voltages of the two secondary windings are measured by the alternating-current voltmeter (6) to try to explain experimental data.

And fifthly, disconnecting the switch, pulling out the plug, dismantling the circuit and arranging the equipment.

Experimental data: in a certain experiment, when the transformer is in no-load (no small bulb is connected), the input voltage between the fifth binding post (405) and the sixth binding post (406) is measured to be 4.69V, the output voltage between the first binding post (401) and the second binding post (402) is measured to be 9.27V, and the output voltage between the third binding post (403) and the fourth binding post (404) is measured to be 2.31V. After the transformer (4) supplies power to the small bulb (3), the input voltage drop of the transformer (4) is 4.48V, the output voltage drop between the first terminal (401) and the second terminal (402) (connected with the small bulb (3)) is 6.85V, and the output voltage drop between the third terminal (403) and the fourth terminal (404) is 1.78V.

And (4) experimental conclusion: when the transformer is in no-load (no small bulb is connected), the output voltage between the first binding post (401) and the second binding post (402) of the transformer (4) is 2 times of the input voltage, and the output voltage between the third binding post (403) and the fourth binding post (404) is 0.5 times of the input voltage, so that the transformer ratio formula of the transformer is quite good. After the transformer (4) supplies power to the small bulb (3), the input voltage and the output voltage are not reduced in the same proportion. The output voltages of the second coil (4b) and the third coil (4c) of the two secondary coils are compared with the formula

Is one section lower. Because the primary coil and the secondary coil of the transformer have resistors, the heating loss (copper loss) generated by the current in the two coils is larger, the iron loss is larger than that in the idle state, the voltage of the two ends of the secondary coil connected with the bulb is lower than the formula predicted value, and the voltage of the two ends of the other idle secondary coil (between the third binding post (403) and the fourth binding post (404)) is also lower than the formula predicted value.

In this embodiment, a boost power supply circuit is adopted, and certainly, an experiment can be performed by adopting a buck power supply circuit. Such as: a first coil (4a) of the transformer (4) is connected with a low-voltage alternating current power supply (5); a third coil (4c) with 2n turns supplies power to a small bulb (3) with 2.5V and 0.3A, and a second coil (4b) with n turns is unloaded. An alternating current voltmeter (6) is used for measuring input voltage between a first binding post (401) and a second binding post (402) of the transformer (4), output voltage between a fifth binding post (405) and a sixth binding post (406), and output voltage between a third binding post (403) and a fourth binding post (404).

Example 6 boost power supply test experiment

Purpose of the experiment: attempts to utilize transformer boost supply tests have revealed that small transformers are not ideal.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of a transformer (4) used in the experiment is respectively 4n, n and 2n, the direct current resistance values of the three coils are not greatly different, a low-voltage power supply (5) is a low-voltage alternating current power supply, the specification of a small bulb (3) is 6.3V and 0.15A, and the measuring range of an alternating current voltmeter (6) is 20V.

The experimental steps are as follows: in the first step, a third coil (4c) with 2n turns of a transformer (4) is connected with a low-voltage alternating-current and direct-current power supply (5), the output voltage selects an alternating-current 4V gear, a first coil (4a) with 4n turns supplies power to a small bulb (3) with the specification of 6.3V and 0.15A, and a second coil (4b) with n turns is unloaded.

And secondly, inserting a power plug into a socket (with the voltage of 220V), switching on the power supply, and observing the light emitting condition of the small bulb (3).

The exploration and prompt are as follows: the input end of the transformer (4) is connected with an alternating current 4V gear, the actually measured input voltage is about 4.5V, and the turn ratio of the primary coil to the secondary coil is 1:2, note that it is observed whether a small bulb rated at 6.3V will break.

And thirdly, measuring the input voltage and the output voltage (namely the voltage at two ends of the small bulb) of the transformer (4) by using the digital multimeter (6), and selecting an alternating current 20V gear in the measuring range.

Fourthly, trying to explain the experimental phenomenon, pulling out the plug, switching the switch of the digital multimeter (6) to an OFF position, dismantling the circuit and arranging the equipment.

Experimental data: in a certain experiment, the small bulb (3) normally emits light when power is supplied, the input voltage of the transformer (4) is measured to be 4.52V, and the output voltage of the secondary coil is measured to be 6.97V.

And (4) experimental conclusion: the primary and secondary coils in the transformer are wound on the frame and insulated from each other, and the working principle of the transformer is the mutual inductance principle in electromagnetic induction. Experimental data show that the output voltage of the transformer when the transformer is connected with a small bulb is lower than the predicted value of an ideal transformer transformation ratio formula. This is because the transformer is not ideal, the primary and secondary windings have large resistance, the heating loss (copper loss) generated when the current passes through the windings is large, the iron loss is also large compared with the no-load, and the output voltage is reduced. And the coil current is zero when the coil is in no load, and the copper loss is negligible.

Example 7 step-down Power supply test experiment

Purpose of the experiment: the transformer step-down power supply principle is understood. It is not ideal to know small transformers.

Preferably, the method comprises the following steps: the number of turns of a first coil (4a), a second coil (4b) and a third coil (4c) of a transformer (4) used in the experiment is 4n, n and 2n respectively, the direct current resistance values of the three coils are not greatly different, a low-voltage power supply (5) is a low-voltage alternating current power supply, the specification of a small bulb (3) is 2.5V/0.3A, and the measuring range of an alternating current voltmeter (6) is 20V.

The experimental steps are as follows: in the first step, a first coil (4a) with 4n turns of a transformer is connected with a low-voltage alternating-current and direct-current dual-purpose power supply (5), an alternating-current output 6V gear is selected, and a third coil (4c) with 2n turns supplies power to a small bulb (3) with the specification of 2.5V/0.3A.

And secondly, inserting a power plug into a socket (with the voltage of 220V), switching on the power supply, and observing the light emitting condition of the small bulb (3).

And thirdly, measuring the input voltage and the output voltage (namely the voltage at two ends of the small bulb) of the transformer (4) by using the digital multimeter (6), and selecting an alternating current 20V gear in the measuring range.

And fourthly, pulling out the plug, dialing the switch of the multimeter to an OFF position, dismantling the circuit and arranging the equipment.

Experimental phenomena: when power is supplied, the small bulb (3) normally emits light, but the output voltage of the transformer (4) when the small bulb is connected is lower than the predicted value of the transformation ratio formula.

And (4) experimental conclusion: the turn ratio of the primary coil to the secondary coil of the transformer is 2: 1, according to a transformation ratio formula of an ideal transformer, the voltage at two ends of the secondary coil is half of the input voltage. In a certain experiment, when the transformer supplies power to a small bulb, the measured input voltage is 6.87V, and the output voltage of the secondary coil is only 2.44V, because the transformer is not ideal, the coil has resistance values, the copper loss and the iron loss are large during power supply, and the output voltage is much lower than the predicted value of a formula.

The technical scheme has the following beneficial effects:

1. the Faraday's law of electromagnetic induction is an important law of high school physics, and although the scholars propose experimental technical schemes, the Faraday's law of electromagnetic induction is high in cost and relatively complex in operation. In the practical teaching of physics of high school, the condition of limiting to middle school's laboratory, it is difficult to carry out quantitative verification, and the teacher can only combine the physics history to introduce the Faraday electromagnetic induction law directly, is unfavorable for student's understanding and grasp. The technical scheme utilizes a simpler device to quantitatively verify the Faraday's law of electromagnetic induction, and has good effect and low cost (and the equipment is shared with many experiments).

2. The outage self-induction phenomenon experiment is a demonstration experiment which is necessary to be done in a middle school physics classroom, the outage self-induction phenomenon experiment is done by a 2446 type self-induction phenomenon demonstrator of a school, although a small bulb can be observed to flash and extinguish once, misunderstanding of a plurality of students can be caused, the self-induction electromotive force generated by a coil is considered not to exceed the original power voltage (because the power voltage is 4V, the rated voltage of a small lamp is also 4V), and meanwhile, factors influencing the experiment effect cannot be explored by a school scheme (only one large coil). In the technical scheme of the invention, a power supply is 3V (2 dry batteries), in the embodiment 2, the specification of the small bulb is 6.3V and 0.15A, when the switch is closed, the small bulb is slightly on, and when the switch is turned off, the 6.3V small bulb is suddenly turned on and is extinguished. The fact that when a student powers off the circuit, the induced electromotive force generated by the coil is much higher than the power supply voltage is more convincing. In experimental example 3, the specification of the small bulb is changed to 2.5V and 0.3A, a rheostat is added in the circuit, in both embodiments, three coils of the transformer are respectively tested in the experiment, so that students can recognize the first condition that the small bulb is brighter through analysis and comparison of experimental phenomena that: the current through the coil before the switch is turned off is much greater than the current of the small bulb; the second condition is: the self-inductance of the coil is sufficiently large. It can also be understood that the self-inductance of the coil is related to the thickness and the number of turns of the coil, and the thicker the coil, the more the number of turns, and the larger the self-inductance by adding the iron core. These effects are all that the current experimental scheme of school can't reach.

3. The existing experimental scheme of school can only demonstrate the blocking effect of one coil (inductor) on alternating current. The experiment is also carried out in the embodiment 2 of the scheme of the invention, because the wire diameters and the turns of the three coils in the transformer are properly designed, the hindering effects of the three coils on the alternating current in the experiment are greatly different, which just represents three typical conditions, and the perfect experiment effect is achieved. The wire diameter of the first coil (4a) with 4n turns is thick, the self-inductance coefficient is large, the effect of conducting direct current and blocking alternating current is achieved in the experiment, and the low-frequency choke coil can be considered as a low-frequency choke coil. The second coil (4b) with n turns has a small wire diameter and a small self-inductance, can allow low-frequency alternating current to pass through the coil, but also has an inhibiting effect, and can be considered as a high-frequency choke coil. The third coil (4c) of 2n turns exhibits a characteristic in between.

The experiment of 'exploring the relation between the voltage at two ends of the transformer coil and the number of turns' is arranged by a teaching material into a classroom exploration experiment and a student experiment. The experiment of the student who needs manual work is similar to the nominal experiment in most mathematics schools, and the main reason is that the experiment result obtained by school equipment (transformers) is greatly different from the theoretical prediction value. Because of in school "The detachable transformer for teaching has large loss (magnetic leakage, iron core eddy current and the like) in no-load, and the voltage value measured by the secondary coil is less than 80% of the theoretical predicted value (the result is about 75%). When the transformer is used for the experiment, the voltage value measured by the auxiliary coil during no-load reaches more than 99% of the theoretical predicted value. Therefore, the transformation ratio formula of the ideal transformer is summarized and obtained in a water-to-channel manner, and the reliability is high. In example 5 of the inventive solution, the voltage across the transformer coil was again investigated in the case of a supply. The output voltage ratio formula of two secondary windings of the transformer under the condition of power supply is found through measurement

Is one section lower. The students can recognize the difference between the actual small-sized transformer and the ideal transformer in the process of explaining the phenomenon, and the capability of solving relevant actual problems is improved.

5. The technical scheme can complete more than twenty experiments (slightly increasing point devices) related to electromagnetic induction, and comprises the steps of exploring the generation condition of induced current (magnet is close to a coil), exploring the generation condition of the induced current (experiment simulating Faraday), exploring a method for judging the direction of the induced current (Lenz law), quantitatively exploring Faraday electromagnetic induction law (I), quantitatively exploring Faraday electromagnetic induction law (II), power failure self-induction phenomenon (a dry battery lights a 220V illuminating lamp), power failure self-induction phenomenon (safe experience electric shock experiment), power failure self-induction phenomenon (a small bulb experiment scheme), factors influencing the power failure self-induction effect, an exploration experiment of the power failure instant self-induction phenomenon, exploration experiment of the blocking effect of an inductor on alternating current and power failure mutual induction phenomenon (a dry battery lights a 220V) and, The method comprises the following steps of power failure mutual inductance phenomenon exploration (safety experience electric shock experiment), power-on instant mutual inductance phenomenon exploration (jump ring experiment), voltage and turn number relation exploration (quantitative exploration Faraday electromagnetic induction law III) at two ends of a transformer coil, boosting power supply test experiment, voltage-reducing power supply test experiment, exploration of the fact that when the transformer is connected with a direct-current power supply, electric energy can not be transmitted, voltage at two ends of the transformer coil under the power supply situation, voltage at two ends of the transformer coil under the magnetic leakage situation and the like, and is good in effect and low in cost. The technical scheme further solves the problem of high school physics experiments and better cultivates the physics experimental ability of students.

The present invention has been described in terms of embodiments, and a number of variations and improvements can be made without departing from the present principles. It should be noted that all the technical solutions obtained by means of equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims (7)

1. An electromagnetic induction exploration tester is characterized by comprising a transformer (4), an ammeter (2), a small bulb (3), a rheostat (1), a low-voltage power supply (5), an alternating-current voltmeter (6) and a switch (7); the transformer (4) comprises a first coil (4a), a second coil (4b) and a third coil (4 c); a first binding post (401) and a second binding post (402) are respectively arranged at two ends of the first coil (4 a); a third binding post (403) and a fourth binding post (404) are respectively arranged at two ends of the second coil (4 b); a fifth binding post (405) and a sixth binding post (406) are respectively arranged at two ends of the third coil (4 c); the low-voltage power supply (5) is an alternating current and direct current dual-purpose low-voltage power supply or a combination of an independent low-voltage alternating current power supply and an independent low-voltage direct current power supply.

2. An electromagnetic induction exploration tester as claimed in claim 1, characterized in that said first coil (4a), said second coil (4b) and said third coil (4c) have n turns respectively₁、n₂、n₃，n₁Greater than n₃Greater than n₂The resistance values of the three coils are not greatly different, and when one coil is selected to be connected in series with the ammeter (2) to form a closed circuit each time, the total resistance values of the three closed circuits are approximately equal and the difference is not more than 20%.

3. An electromagnetic induction exploration tester as claimed in claim 2, characterized in that a coil of said low voltage power supply (5), switch (7), varistor (1) and transformer (4) are connected in series to form a closed circuit; the ammeter (2) is connected with the remaining coil of the transformer (4) in series to form another closed circuit, and the low-voltage power supply (5) is a low-voltage direct-current power supply.

4. An electromagnetic induction exploration tester as claimed in claim 1, characterized in that the first coil (4a) or the second coil (4b) or the third coil (4c) of said transformer (4) is connected in series with the small bulb (3), the switch (7) and the low voltage power supply (5) to form a closed circuit.

5. An electromagnetic induction exploration tester as claimed in claim 1, characterized in that said small bulb (3) is connected in parallel with the first coil (4a), or the second coil (4b), or the third coil (4c) of the transformer (4) and then connected in series with the low voltage power supply (5); the low-voltage power supply (5) is a low-voltage direct-current power supply.

6. An electromagnetic induction exploration tester as claimed in claim 1, wherein said small bulb (3) is connected in series with said varistor (1) and then connected in parallel with said first (4a) or second (4b) or third (4c) winding of said transformer (4) and then connected in series with said low voltage power supply (5), said low voltage power supply (5) being a low voltage dc power supply.

7. An electromagnetic induction exploration tester as claimed in claim 1, characterized in that a coil of said transformer (4) is connected to a low voltage power supply (5); the small bulb (3) is connected with the remaining coil of the transformer (4) in series; measuring input voltage or output voltage between a first terminal (401) and a second terminal (402), between a third terminal (403) and a fourth terminal (404), and between a fifth terminal (405) and a sixth terminal (406) of the transformer (4) by using an alternating voltage meter (6); the low-voltage power supply (5) is a low-voltage alternating current power supply.

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