Английский язык: Методические указания и задания к контрольным работам для студентов специальности «Техническая эксплуатация транспортного оборудования», страница 4

1. Некоторые вещества содержат много свободных электронов. 2. Такие вещества называются проводниками электричества. 3. Изолятор (диэлектрик) -  вещество, которое не содержит свободные электроны. 4. Свободные электроны освобождают электрическую энергию. 5. Электрическая энергия может освобождаться посредством химической реакции, электромагнитной индукции и трения. 6. Электрический ток – это протекание электронов по проводнику. 7. Сила, которая заставляет электроны двигаться называется разностью потенциалов или электродвижущей силой (эдс). 8. Когда электроны текут в одном направлении, ток называется постоянным. 9. Когда электроны текут сначала в одном направлении, затем в другом направлении периодически, ток называется переменным.

Задание №6. Ответьте на вопросы:

1. What do we call the substances which contain many free electrons?

2. What is an insulator?

3. What insulators do you know?

4. What is an electric current?

5. What current is called a direct current?

6. What current is called an alternating current?

7. What conditions are needed to make an electric current flow?

Вариант №3

Задание №1. Прочитайте и переведите текст письменно:

RESISTANCE

When a conductor has different potentials at its ends, the free electrons of the conductor flow from one end to the other. For a continuous flow the potential difference must be maintained by some source of electricity such as a generator or battery. The conductor and the electrical source form an electric circuit. For practical needs a load is usually included into the circuit. You need to know three basic circuit properties to understand radio theory. They are: resistance, inductance and capacitance.

In 1827 George Ohm, a German physicist, discovered a relationship between current, electromotive force (voltage) and resistance. Ohm’s law is expressed by the equation

I =

(value of current equals electromotive force divided by resistance).

For instance, Ohm noticed that more current flows through a copper wire than through an iron wire of the same size, and that more current flows through a thick wire than through a thin wire of the same material. George Ohm discovered that some types of materials resist the flow of current more than others. Resistance tends to reduce the amount of current that is flowing through the circuit. The resistance of a conductor depends on the following parameters: the type of material, its cross-section and length.

Ohm then connected a cell with a higher e.m.f. (voltage) to the same conductor and he discovered that more current flowed into the circuit. In other words, resistance is a constant ratio of electromotive force to current in this conductor:

        or      (which is the same)

George Ohm proved that only voltage and resistance affect the amount of current. In most conductors the resistance is greater when they are hot and less when they are cold.

VOCABULARY