Exercise 1. Answer the questions

Exercise 1. Answer the questions

1. What is a resistor used for?

2. When does the temperature of a resistor rise?

3. What element is used to change the value of voltage?

4. How are resistors rated?

5. What types of resistors are there?

6. When does a resistor get open?

7. What does an open resistor result in?

8. What is the difference between a fixed resistor and a variable re- sistor?

 

Exercise 2. Translate into English

1. Резисторы используются для уменьшения тока в цепи.

2. Когда ток проходит через резистор, его температура повыша-

ется.

3. Постоянные резисторы имеют постоянное значение сопротив-

ления.

4. Если величина сопротивления может быть изменена, то это переменный резистор.

5. Переменные резисторы состоят из резистивной дорожки и ползунка.

 

Unit 5. Relays

Vocabulary

to allow                                позволять, разрешать

lever                                     рычаг

magnetic field                      магнитное поле

relay coil                              катушка реле

separate                                отдельный; обособленный

set                                         набор (совокупность)

 

Text

A relay is an electrically operated

switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and connects or disconnects the switch contacts. The coil current can be on or off so relays have two switch positions.

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example, a low voltage battery cir- cuit can use a relay to switch a 230V AC mains circuit. There is no electri- cal connection inside the relay between the two circuits; the link is magnet- ic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to op- erate from lower voltages.

Relays can have many sets of switch contacts. The relay’s switch connections are usually labeled COM, NC and NO:

·

COM = Common, always connect to this; it is the moving part of the switch.

· NC = Normally Closed, COM is con- nected to this when the relay coil is off.

· NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when the relay coil is off.