Vocabulary and Text

Vocabulary

cheap                           дешевый

common                      общий, распространенный

conductor                    проводник

copper                         медь

to decrease                  уменьшаться

difficulty                     трудность

to increase                  возрастать, увеличиваться

insulator                      изолятор

load                             нагрузка

load resistance            сопротивление нагрузки

make smb do smth     заставить кого-л. сделать что-л.

resistance                    сопротивление resistance material                                    резистивный материал rubber                                    резина

since                            так как

thus                             так, таким образом

voltage drop                падение напряжения

 

Text

Conductors are materials having a low resistance so that current easi-

ly passes through them. The lower the resistance of the material, the more current can pass through it.

The most common conductors are metals. Silver and copper are the best of them. The advantage of copper is that it is much cheaper than sil- ver. Thus, copper is widely used to produce wire conductors. One of the common functions of wire conductors is to connect a voltage source to a load resistance. Since copper wire conductors have a very low resistance, a minimum voltage drop is produced in them. Thus, all of the applied volt- age can produce current in the load resistance.

It should be taken into consideration that most materials change the value of resistance when their temperature changes.

Metals increase their resistance when the temperature increases while carbon decreases its resistance when the temperature increases. Thus, met- als have a positive temperature coefficient of resistance while carbon has a negative temperature coefficient. The smaller is the temperature coefficient or the less the change of resistance with the change of temperature, the more perfect is the resistance material.

Materials having a very high resistance are called insulators. Current passes through insulators with great difficulty. The most common insula- tors are air, paper, rubber, plastics.

Any insulator can conduct current when a high enough voltage is ap- plied to it. Current of great value must be applied to insulators in order to make them conduct. The higher the resistance of an insulator, the greater the applied voltage must be.

When an insulator is connected to a voltage source, it stores electric charge and a potential is produced on the insulator. Thus, insulators have two main functions: to isolate conducting wires and thus to prevent a short between them; to store electric charge when a voltage source is applied.