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Тeма уроку: Навички усного спілкування: Thermionic Valves or Tubes. Diode

Тип уроку: урок-узагальнення

Мета уроку: розвинути в учнів комунікативні навички.

Завдання уроку: опрацювати лексику з теми; скласти та «програти» діалоги (учень – учень) з відповідною лексикою; відповісти на запитання та виконати завдання для узагальнення та систематизації вивченого.

Хід уроку:

Завдання 1

Translate the following text.

Thermionic Valves or Tubes. Diode

The branch of electronics dealing with the emission of electrons from substances under the action of heat, particularly the study and designs of thermionic valves or tubes is called thermionics. A good high vacuum is practically a perfect nonconductor, since in it no carriers of electricity are present. If two metal plates or electrodes are enclosed in a vacuum by a glass tube, we have an open circuit and no current will flow. However, one of the electrodes being heated to a high temperature, the thermal velocity of some of the conduction electrons in the metal becomes high enough for these electrons to escape. In moving through a vacuum these electrons form an electric current. The effect of thermionic emission is due to the fact that some of the electrons in metal under certain conditions can obtain such a velocity, that their kinetic energy is great enough to overcome forces of attraction and so they may leave the metal surface. The mean velocity of the electrons in the metallic conductor is not high enough to cause more then a very small percentage of the electrons to be ejected. Nevertheless, the electrons leaving the metal surface can produce considerable currents. Electrons can as well escape from cold metal surfaces in case they are acted upon by so high an electric field (approximately 107 volt/cm or more), that the molecular forces of attraction are overcome by it. A thermionic valve is a system of electrodes arranged in an evacuated glass or metal tube. For special purposes gas at low pressure may be introduced into the valve. The heated electrode is called the cathode (or sometimes the filament) and the cold electrode-the plate. The cathode is an electrode which is held at a negative potential to the plate. It emits electrons. The cathode of a tube may be in the form of a wire which is heated or it may be a metal tube coated with certain metallic oxides, which is heated by a separate heater. In the former case the cathode is known as “filament”, in the latter, it is called an “indirectly heated cathode”. In both cases the heating of a substance causes it to emit electrons. The device is called a diode and if we apply an alternating current to a vacuum tube it behaves as a oneway resistance, electrons move from cathode to plate but not from plate to cathode.

Цікаво знати!

Diodes are usually referred to as D for diode on PCBs. Sometimes the abbreviation CR for crystal rectifier is used.

Завдання 2

Write 5 questions to the text and answer them.

Завдання 3

Trаnslаte the fоllоwіng wоrd соmbіnаtіоns іntо Ukrаіnіаn. Then wrіte а dіаlоgue wіth the wоrds аnd асt it.

Електронно-променева трубка; емісія електронів; гарний ізолятор; рух струму; швидкість носіїв заряду; металева поверхня; перевищувати сили тяжіння; діяти високим електричним полем; заповнювати електронно-променеву трубку газом низького тиску; нитка накалювання; анод; покривати металевими оксидами; катод; який непрямо нагрівається; змінний струм; опір в одному напрямку.

Перевіртe себе (запитання до тексту)

1 What do we call thermionics?

2 Why is a good vacuum a perfect nonconductor?

3 Why do electrons escape from a heated electrode? What else can cause the escape of electrons from metal surfaces?

4 What do they form in the evacuated glass tube?

Cпиcoк викориcтаної літeрaтури:

1. Урок на тему: «Навички усного спілкування» учителя ЗОШ № 142 Стехінa О. О., м. Запоріжжя.

2. Ю. Б. Гoліцинcький. Spoken Еnglіsh. Пocібник з рoзмoвнoї тeми — 2010

3. www.provost.harvard.edu

4. en.wikipedia.org

Cкoмпoнoвaнo та відредагoвaнo Кaмoнгaр Г. Н.

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