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Кабiнет 45

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Автор Повідомлення
 Заголовок повідомлення: Заняття 2 ( 7 семестр)
ПовідомленняДодано: 19 жовт 2019, 19:23 
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Зареєстрований: 17 черв 2014, 17:23
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Заняття 2 ( 7 семестр)


Тема: Електронні випрямлячі. Згладжувальні фільтри. Багатозначність слів. Торic. Rectifiers. Polisemanticy of words.


1. Read and translate the text “Rectifiers”

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Rectifiers are devices designed to convert alternating current into direct current. For this purpose devices with asymmetrical conductance such as vacuum and semiconductor diodes are used. Until the end of the twenties of this century vacuum diodes (kenotrones) were the main rectifying devices. In the thirties highpower kenotrones were replaced by more efficient mercury vapour rectifiers. At present high-power gas-filled and gas-control tubes are used. Low-power rectifiers mostly used in low and medium power rectifying systems are replaced by highly efficient and reliable semiconductor rectifiers.

The simplest types of rectifiers:


a) Half wave rectifiers.

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b) Full-wave rectifiers

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A rectifier can take the shape of several different physical forms such as solid-state diodes, vacuum tube diodes, mercury arc valves, silicon-controlled rectifiers and various other silicon-based semiconductor switches.


Rectifiers are used in various devices, including:

· DC power supplies

· Radio signals or detectors

· A source of power instead of generating current

· As flame rectification to detect the presence of flame

· High-voltage direct current power transmission systems

· Several household appliances use power rectifiers to create power, like notebooks or laptops, video game systems and televisions.



2. Form derivatives from:

to convert, to conduct, to rectify, efficient, to relate, to resist.



3. Translate the following terms and memorize them:

vacuum diodes, output voltage, a load resistor, transformer secondary, full-wave rectifiers, pulsating wave-form, mercury vapour rectifiers.



4. Translate into English.

1.Випрямлячі – це пристрої, що перетворюють змінний струм в постійний.

2. До кінця 20-х років основними випрямними елементами були вакуумні діоди (кенотрони), які виготовлялися потужністю від кількох ват до декількох десятків кіловат.

3. Потужні кенотрони були в 30-х роках витіснені більш економічними ртутними випрямлячами, розробленими під керівництвом академіка В. П. Волощина.

4. В даний час застосовують також потужні газотрони і тиратрони.



5. Open the brackets. Use the necessary words.

1. A rectifier is an electrical (gadget/device) composed of one or more diodes that converts alternating current (AC) to direct current (DC).

2. A diode is like a (one-way/two-ways) valve that allows an electrical current to flow in only one direction. This process is called rectification.

3. Rectification produces a type of DC that encompasses active voltages and currents, which are then (adjust/adjusted) into a type of constant voltage DC, although this varies depending on the current's end-use.

4. The current is allowed to flow uninterrupted in one direction, and no current is allowed to flow in the (same/opposite) direction.

5. Almost all rectifiers contain (many/more) than one diode in particular arrangements.

6. A rectifier also has different (waveform/waveforms), such as:

• Half Wave: Either the positive (or/nor) negative wave is passed through and the other wave is blocked. It is not efficient because only half of the input wave (form/forming) reaches the output.

• Full Wave: Reverses the negative part of the AC wave form and combines (it/its) with the positive

• Single-Phase AC: Two diodes can form a full-wave rectifier if the transformer (is/will be) center-tapped. Four diodes arranged in a bridge are (need/needed) if there is no center-tap.

• Three-Phase AC: Generally uses three (pair/pairs) of diodes

One of the key problems with rectifiers is that AC power has peaks and lows, which may not produce a constant DC voltage. Usually, a smoothing circuit or filter needs to be coupled with the power rectifier (to/too) receive a smooth DC current.



6. Read the text and say what parts of speech are underlined words.

Rectifiers

There are many applications of' electricity where, for technical reasons, D. C. is preferable to A. C. It is necessary to have some means of obtaining D. O. from an A.C. source, and this requirement is met by one or other of the numerous forms of rectifiers.

A metal rectifier, a widely used form of rectifier, is the metallic type consisting essentially of a number of units formed by depositing a layer of semiconducting material, such as copper oxide on a metal conducting base. These units, generally in the form of washers, are assembled on rods under pressure, the number of units employed being determined by the voltage. Each unit has the peculiar property of passing current freely when the semi-conducting layer is positive and allowing practically no current to flow in the opposite direction. This form of rectifier has the great advantage of strength, absence of moving parts and relative simplicity.

A valve rectifier. Another type of rectifier is represented by various kinds of two-electrode valves, or diodes. These consist of a glass tube or bulb containing an electron-emitting member (the cathode) and an electrode (called the anode) which collects the emitted electrons and causes a flow of current so long as it is positive with respect to the cathode. The cathode heater is supplied with a suitable voltage from the transformer secondary to provide the heating necessary for the emission of electrons. The action of the tube differs some¬what according to whether it is of the high vacuum or gas-filled type. The rectifying property of the diode valve arises from the fact that electrons can flow from cathode to anode only when the latter is positive with, respect to the cathode. The electrons, having a negative charge, are attracted by the positive plate, thus causing a flow of current through the tube and the external circuit.



7. Find in every column group of words which can be predicate in sentences.

A was developed;is being insulated ;being heated ;can be called

B these results ; has been discovered ;are moving ;does not carry

C generates; generators;flows;should be done



8. Exercises: Translate the following sentences with polysemantic words:


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Facility

1. The college has excellent facilities.

2. The phone is equipped with a call-back facility.

3. There was also fierce local opposition in June to plans to build the world’s largest nuclear waste facility near Krasnoyarsk.

4. The hotel has its own pool and leisure facilities.

Challenge

1. The company is ready to meet the challenges of the next few years.

2. I like the challenge of learning new things.

3. In school, Clint was a real challenge to all of his teachers.

4. The president faces a strong challenge from nationalists.

Record

1. As an employee, his record is outstanding.

2. Medical records are now kept on computers.

3. The department has a long record of high achievement.

4. The industry’s record on environment conservation is not very impressive.

Commitment

1. Many parents do not get involved in schools because they have too many other commitments.

2. Thanks to your energy and commitment, the fundraising campaign was a great success.

3. The US President expressed America’s commitment to Africa’s economic development.

4. The country is hoping for a commitment of $25 million in aid.

5. The governor has a strong commitment to creating jobs in the state.

To fail

1. A very high percentage of small businesses fail within their first year.

2. Across the state, corn crops failed due to the drought.

To challenge

1. Billboard companies say they will challenge the new law in court.

2. Guards were ordered to challenge anyone entering the building.

3. He’s a good director – he really challenges us.

4. Many doctors have challenged the accuracy of his findings.

5. I’m really at my best when I’m challenged.



9. You know that many English words are polysemantic. Can you find equivalents to the following words?


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