Text 4. Conductors

1. Прочтите и переведите текст.

Vocabulary:

according to – в соответствии с

to divide – делить, разделять

conductor – проводник

semiconductor - полупроводник

to owe – быть должным

carbon – углерод

electrolyte – электролит

coefficient – коэффициент

resistance – сопротивление

resistivity – удельное сопротивление

nichrome – нихром

heater – нагревательный прибор

According to their conductivity, all materials are divided into conductors, insulators and semiconductors. Conductors allow electricity to pass through them; insulators do not. Conductors are materials having a very high conductivity. A conductor owes its conducting powers to the presence of free electrons, which have broken away from their atoms. The most common of them are metals (copper, aluminum, steel, and others), carbon and electrolytes. Their coefficient of resistance is different. Copper, for example, has a positive coefficient while carbon has a negative coefficient of resistance.

According to their resistivity, conductors are divided into two groups; the first one includes materials with low resistivity; copper, aluminum and others. These metals are used to produce wire conductors due to their high mechanical strength. The second group includes materials with high resistivity; one of these is nichrome. Due to its good heat resistance, nichrome is used to produce heaters. Carbon is commonly used to produce electrodes and brushes for electric machines.

2. Ответьте на вопросы по тексту:

1. Into what groups are materials divided?

2. What do conductors do?

3. What materials are common conductors?

4. Are their coefficients of resistance different?

5. What materials have high mechanical strength?

6. What coefficient of resistance has carbon?

7. What materials are commonly used to produce wire conductors (brushes, heaters)?

3. Выберите правильный вариант:

1. All materials are divided into …

1. conductors and semiconductors: b) conductors, insulators and semiconductors.

2. Copper has …

1. high mechanical strength; b) low mechanical strength

3. Carbon has …

1. a positive coefficient of resistance; b) a negative coefficient of resistance.

4. Copper is commonly used to produce …

1. heaters; b) brushes.

4. Прочитайте по-английски:

18; 1.8; 36 000; 63:7=9; V=IR.

5. Используйте английские слова вместо русских.

1. Any circuit (оказывает) resistance to the flow of current.

2. Resistance (зависит от) the temperature of the conductor.

3. Conductors are divided into groups (в зависимости от) their resistivity.

Text 5. Insulators

1. Прочтите и переведите текст.

Vocabulary:

to offer – предлагать

device – приспособление, механизм, устройство

to isolate – изолировать, разъединять

dielectric – диэлектрик

oil – масло, нефть

resin – смола

cable – кабель

capacitor – конденсатор

amorphous – бесформенный, аморфный

polyethylene – полиэтилен

to include – включать

porcelain – фарфор

Insulating materials have a very low conductivity. They offer extremely high resistance to the flow of current. Insulators are used in electric devices to isolate conductors. Thus, they should have a high dielectric strength and a high resistivity. Their mechanical properties are also important for practical use.

Insulators are divided into gaseous, liquid, and solid. They are also divided into groups according to their heat resistance.

The main gaseous insulator is air. At 20°C, the dielectric strength of air is extremely low; it is lower than the strength of most liquid and solid dielectrics.

Liquid insulators are mineral oils, synthetic liquids, resins, and others. Of them mineral oils are used in oil transformers, cables and capacitors. In transformers, oil is used to insulate current conducting parts. Thus, it should have a high dielectric strength (10 to 20 mv/m). As to resins, at low temperatures they re amorphous. When heated, they become first plastic, then liquid. Resins are the most important components of many plastics. (Commonly used in electrical engineering are synthetic (polymeric) resins – polyethylene). Plastics are used as wire and cable insulation. Solid insulators are paper, cloth, plastics, and porcelain. Of them plastics are widely used in electrical engineering as insulating and structural materials. As to porcelain, it is highly resistant to mechanical factors and heat. Due to this property, it is used to produce low- and high-voltage insulators.

3. Ответьте на вопросы по тексту:

1. What materials offer extremely high resistance?

2. Where are insulators used?

3. What properties of insulators are important for practice?

4. Into what groups are insulators divided?

5. What is the main gaseous insulator?

6. What is the main liquid insulator?

7. In what devices are mineral oils used as insulating materials?

8. What can you say about resins?

9. What happens to resins at low temperature and when heated?

10. What properties have porcelain?

4. Переведите словосочетания:

Amorphous resins; air insulators; porcelain parts; important properties; main properties of capacitors; important parts of devices; solid synthetic resins; practically important part; extremely low conductivity; commonly produced porcelain insulator.

5. Переведите предложения, обращая внимание на слово «thus»:

1. The value of current should be the same in the elements of the circuit; thus they should be connected in series.

2. Porcelain is highly resistant to heat, thus it is commonly used to produce insulators.

6. Выберите правильный вариант:

1. Insulators offer …

1. extremely high resistance: b) extremely low resistance

2. They should have …

a) a high dielectric strength; b) a low electric strength

3. Their mechanical properties …

a) are important for practice; b) are not important for practice

4. Commonly used insulating materials are …

a) liquid; b) gaseous; c) solid