Methods of Producing Cathode Rays i.e. Streams of Electrons

Methods of Producing Cathode Rays i. e. Streams of Electrons

1. It is now almost common knowledge¹ that the atom consists of a very small a nucleus possessing most of the atom’s mass with one or more electrons round it. The nucleus carries a positive charge equal to the total charge of its electrons so that an atom in its normal state is electrically neutral. We get electrons by detaching them from atoms. In the discharge tube this occurs by the impact of positive ions with cathode, a few such ions being always present in a gas. The intense electric field between anode and cathode accelerates these ions towards the cathode, and bombardment detaches electrons in the direction of the anode.

2. Another way of getting electrons is simply to heat metal coated with certain oxides, such as barium oxide. A pure metal, as, for example tungsten, has to be made white hot before it will emit enough electrons, but these oxides emit them at very much lower temperatures. The electron stream in radio valve, for instance, is produced in this way. We may suppose that the electrons are detached from atoms as a result of thermal agitation.

3. Light falling on some metals, e. g. ² cerium³, will also cause emission of electrons, and the shorter the wavelength of light, the more effective it is. Ejection of electrons by radiation is called the photoelectric effect and is made use of ⁴ in photoelectric cells with their many applications.

Пояснения к тексту:

1. it is … common knowledge – общеизвестно

2. e. g. – exempli gratia – лат. например

3. cerium – церий

4. is made use of = is used

Задание 8. Выпишите из текста предложения, содержащие наиболее полный ответ на поставленный вопрос.

What is called the photoelectric effect?

[1] В наличии в библиотеке колледжа