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Gulyaeva T.V., Ershov A.V., Gulyaeva L.V., Zelenina E.A.

“JACOB'S LADDER” AS AN EXAMPLE OF PROBLEMATIC LECTURE

DEMONSTRATION

T.V. Gulyaeva, Ukraine, the candidate of technical Sciences, associate Professor, Zaporizhzhya national technical University

A.V. Ershov, Ukraine, Doctor of technical Sciences, Professor, Zaporizhzhya national technical University

L.V. Gulyaeva, Ukraine, the candidate of pedagogical Sciences, associate Professor, Zaporizhzhya national technical University

E.A. Zelenina, Ukraine, Graduate student, Zaporizhzhya national technical University

Abstract The paper proposes an experimental installation of “Jacob's Ladder”

during a lecture demonstration of the phenomenon of the electric arc for students of higher technical educational institutions. Involvement of students in preparing lecture demonstrations, promotes productive use of teaching methods - problem and the partial search; implementing a principle of learning - improving the consistency, generality, functionality, physical knowledge, development of competences of students, skills of their success on the international labour market.

Keywords: electric arc, a master oscillator, high voltage transformer, concept. productive methods of training, consistency, generality, functionality of physical knowledge.

Introduction. High school [1] is a logical continuation of the educational policy of

the school profile. After graduating from full school, the pupils are to be formed of key, subject-specific, interdisciplinary competence [2,3]. When higher education students, teachers of higher educational institutions continue the formation of acquired competences students, in terms of their chosen specialty according to educational programs. The main task of the teacher of physics of the technical University is to help students understand the importance of using the acquired academic knowledge, skills, and values in their future professional activities.

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After analyzing government requirements for the future electrical engineer [4,5], and identify the interdisciplinary connections processed the contents of the basic course of General physics [6]. In the study course of General physics, special attention should be paid to improving experimental skills, development of analytical and creative abilities of students. To do this, in the performance of independent and individual work of students should not only gain academic knowledge, but also learn how to use them in project activities [7].

The purpose and objectives. According to the regulations concerning the basic complete higher

education, the passport of profession "Engineer in the energy sector" and curricula of specialties (141-power engineering, electrical engineering, 131-journal of Applied mechanics, 136-metallurgy, 192-Construction and civil engineering), analysis lterature sources as for the demonstration of the phenomenon of spark discharge, to construct a device to:

lecture demonstrations for physics in higher technical school on the topic: "electric current in gases" involving students

-introduction of productive methods, tools, principles of learning. The results of the research. One of the classic methods of training in

higher technical schools is the lecture, which is held according to the following plan: clarifying the aim, the students with the help of lecturer objectives of the lecture, the nomination of hypotheses, identification of contradictions, finding ways to solve the problem, bring the evidence, conclusions regarding the training material, training sessions.. During lectures between the lecturer and audience dialogue takes place, providing diagnostics, getting teacher feedback about the quality of the perception and assimilation of material by students. A lecture should be a complete, complete exercise, contribute to the development of competence of students, skills of success in the international labor market, namely: problem solving, coordination and communication, statements, judgments, efficiently and quickly to make decisions, develop critical thinking and the like.

One of the means of concentration of attention of students is demonstration experiment. So, demonstration – a visual representation of something [8],i.e. lecture demonstration in physics – a visual representation of any physical phenomenon during lectures. During a lecture demonstration there is a possibility puts the problematic issues and tasks, to clarify the connection between scientific physical knowledge and possibility of their use in modern technology. Thus, lecture-demonstrations during the educational process in physics is introduced with the aim of using productive methods of teaching: problematic and partial search; implementing a principle of learning - improving the consistency, generality, functionality of physical knowledge.

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A big plus to the professionalism of the lecturer can put in if in the course of lectures students have their own ideas about the creation of equipment for lecture demonstrations devoted to any topics in physics [9,10].

Thus, problematic lecture demonstration in physics – a demonstration, which is offered, develop, manufacture the equipment and put the students under experiment. the guidance of the teacher on the basis of ZUN obtained in the previous stage of training.

An example of such a collaboration of students and teacher is the creation of experimental installation “Jacob's Ladder” to demonstrate the phenomena of the electric arc [11,12]. In Fig. 1 is a perspective view of the unit. The installation was element made by students of gr. E-125сп, electrotechnical faculty of Zaporizhzhya national technical University Alexey Yatsenko and Artem Levchenko under the guidance of associate Professor of physics ZNTU Gulyayeva Tatyana.

Fig. 1 – General view of the experimental setup “Jacob's Ladder”

from its creators. How to use tribute demo installation? For example, to demonstrate

electric current in gases and gas discharges. With this demo installed, you can watch the rise of the high-voltage arc up between two metal wires. The fact that the arc heats the air, which rises up together with the arc, and the arc rises along with the air for one reason – the heated air is less resistance than a cold one.

The advantage of this experimental setup is the clarity of the demonstration and does not require eye protection from ultraviolet radiation. However, you must strictly adhere to safety regulations, because we have 25 kV and attract students who have a Junior specialist diploma, qualified technician - electrician and have the necessary category and group to work in electrical installations up to 1000 V and above.

We will consider the structure and principle of operation of this installation. In Fig. 2 shows the device of the experimental installation “Jacob's Ladder”. This setting is the simplest high-voltage designs.

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Fig. 2 – External view of the apparatus: 1 – germination, 2 – high-

voltage transformer, 3 – master part 4 – cooler, 5 – switch, 6 – source current 7 – case.

A master oscillator. A simple flyback Converter (flyback). UC3845 is

a high quality PWM controller, the maximum operating frequency to 1 MHz. Inside the chip there is an additional amplifier stage, and this means that the output signal of the pre-strengthening is not necessary. The signal from the chip to the transistor is supplied through a current limiting resistor of 10 Ohms, it removes the transfer from the chip, whereby the latter does not overheat during operation

The high voltage transformer. As a high-voltage transformer can be used by TVs-110 L/6 or any other. On the free side shakes the winding 5 turns of wire 1.2-1.5 mm, the primary windings can not touch, they hinder us not, but, if desired, can be removed. Next, collect the inverter and turn on. On the terminal of the secondary winding an arc is formed which reaches up to 3 cm.

The stairs. The distance between the electrodes at the bottom must meet the maximum distance of the arc and between the electrodes at the top – maximum distance hold the arc. The amperage should be less than 5 mA.

Radiator. Necessary for the unit cooling and prevent overheating of the contacts.

The source of current. A constant current source for 6-12 V. Case. A spacious wooden case for superior air circulation to prevent

overheating of parts of the installation. The principle of operation of the circuit of this setup can be explained

in a simplified variant of the scheme (Fig. 3).

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Fig. 3 – Simplified scheme of the installation.

Immediately after switching on (Fig. 3A), the capacitor C2 is

discharged, the transistor is closed, the current transformer no. Begins charging the capacitor, the charging time depends on its capacitance and resistance R1. During charging of the capacitor voltage at its terminals may not be set at the maximum (transient), and the current on the contrary is only limited by resistor R1.

With increasing current in the transformer (Fig. 3b) on the base winding is induced EMF, which, together with the EMF of the capacitor C2 increases the voltage at the base of the transistor, which in turn opens more and increases the EMF in the base winding – turns out the Domino principle. But this process only continues until the saturation concentration or to saturation of the transistor.

Further saturation of the transformer (Fig. 3b) can not continue, and on the base winding EMF disappears, the transistor begins to shut down. Due to energy storage in the transformer core begins to occur inductive output (when disconnecting the inductor from the power source at each end appears EMF opposite in direction to the current, which flows in it to off). This release closes faster the transistor begins to charge the discharged capacitor C2. Here again the vicious circle closes faster transistor – the greater the inductive release comes out, which is still faster closes the transistor. This process comes to a complete depletion of the reservoir. Further, the capacitor C2 is charged from power source (if the release not loaded because the reverse base current and the base capacitance of the transistor small - most of the emission just disappears without doing anything) and the process repeats from the beginning.

Further presenting questions and tasks that can be set in the course of this troubled lecture demonstration.

1. What phenomenon do you observe and how can you explain that?

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2. Where in their future professional activities, you can use this phenomenon?

3. In this installation the output of 25 kV. At the approach of the electrodes to each other, there is a breakdown of the air in the form of a spark discharge. To determine the mean free path of the electrons should be taken into account that the ionization energy of gas atoms is ϕi, V. For the implementation of impact ionization electron gets such energy when moving in an electric field the free path. For the following is specified to use the data of table 1.

Table. 1 – the ionization Potential some gases.

Газ Воздух H2 N2 O2 Ar He ϕi,В 14,4 15,4 15,6 12,1 15,8 24,6 ε 1,00025 1,00027 1,00054 1,000523 1,000545 1,00007 1) build the dependence of the distance between the electrodes, which

occurs the phenomenon of spark discharge and the external environment, assuming that for air d = 4 mm at U = 25 kV and the length of the free path of the electrons between the electrodes from the composition of the external environment, the voltage across the electrodes changes from 15 kV to 35 kV;

2) build the dependence of the mean free path of the electrons on the pressure and temperature of the external environment (tϵ[-30; +50]0C; Рϵ[740; 790] mm Hg.St.);

3) to determine the charge which is concentrated at the electrodes, including their thin filaments with a length of 5 cm for different environments.

Conclusions. The use of lecture demonstration experiment in physics teaching for

students of higher technical educational institutions helps to concentrate attention of students to a better understanding of their academic material that is taught, as well as the development of competences.

Using the experimental setup of “Jacob's Ladder” to demonstrate the phenomena of the electric arc allows students to visualize and see the electric arc. We also believe that under certain circumstances didactically justified creatively delivered a lecture demonstration, especially with students, give more value than a computer simulation of physical experiments, which are increasingly embedded in the teaching of physics.

Didactically Obrenovac computer simulation demonstrate the phenomenon of the electric arc using the experimental setup of “Jacob's Ladder”.

References:

[1] The law of Ukraine № 1556-VII "On higher education" from 01.07.2014 (Zakon Ukrajiny № 1556-VII «Pro vyshhu osvitu» vid

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01.07.2014 r) / [Electronic resource] – access Mode. – URL: http://zakon3.rada.gov.ua/laws/ show / 1556-18. [in Ukrainian]

[2] Resolution of the Cabinet of Ministers of Ukraine No. 1392 "About approval of State standard of basic and full General secondary education" dated 23.11.2011. (Postanova kabinetu ministriv Ukrajiny № 1392 «Pro zatverdzhennja Derzhavnogho standartu bazovoji i povnoji zaghaljnoji serednjoji osvity» vid 23.11.2011.) / [Electronic resource] – access Mode. – URL: http://zakon5.rada. gov.ua/laws/ show/ 1392-2011-%D0%BF/[in Ukrainian]

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