Exercise 1. Answer the questions

Exercise 1. Answer the questions

1. What is a capacitor used for?

2. What are the main parts of a capacitor?

3. What is the function of insulators?

4. What is the difference between a fixed capacitor and a variable

one?

5. What type of insulators do fixed capacitors have?

 

Exercise 2. Choose the correct answer

1. A capacitor is used …                    a) to supply voltage

b) to store energy

2. A capacitor includes …                  a) insulators

b) conducting wires

3. The function of insulators is …      a) to store energy

b) to prevent a short between met- al plates

4. The capacitance of a fixed capacitor

is …

a) constant

b) varied

5. The plates of a variable capacitor … a) can be moved

b) cannot be moved

6. The greater the distance between the

plates, …

a) the greater is the capacitance

b) the less is the capacitance

7. Fixed capacitors have …                a) air insulators

b) paper insulators

Unit 4. Resistors

Vocabulary

to adjust                                регулировать (настраивать)

cermet                                  металлокерамика

circuit board                         печатная схема, плата

fixed resistor                        постоянный резистор

IR drop                                 активное (омическое) падение напряже- ния; падение напряжения на внутреннем активном сопротивлении

to mount                               устанавливать, монтировать

potentiometer                       потенциометр

preset                                    предварительная установка

resistance track                    резистивная дорожка

rheostat                                 реостат

variable resistor                   переменный резистор

wiper                                    ползунок

 

Text

A resistor is one of the most common elements of any circuit. Re-

sistance is the property of a resistor which restricts the flow of charge. Re- sistors are used 1) to reduce the value of current in the circuit; 2) to pro- duce IR voltage drop and in this way to change the value of the voltage.

When current is passing through a resistor its temperature rises high. The higher the value of current, the higher is the temperature of a resistor. Each resistor has a maximum temperature to which it may be heated with- out a trouble. If the temperature rises higher the resistor fails in an open configuration and opens the circuit.

Resistors are rated in watts. The watt is the rate at which electric en- ergy is supplied when current of one ampere is passing at a potential dif- ference of one volt.

Some resistors have a constant value – these are fixed resistors, the value of other resistors may be varied – these are variable resistors.

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves along the track. The track may be made of carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances).

Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track) or as a po- tentiometer with all three connections in use. Miniature versions called presets are made for setting up circuits which will not require regular ad- justment.

In a rheostat two terminals are used: one connected to an end of the track, the other to the moveable wiper. The resistance changes between the two terminals from zero up to the maximum resistance. Rheostats are often used to vary current, for example to control the brightness of a lamp or the rate of charging a capacitor.

Potentiometers have all three terminals connected. This arrangement is normally used to vary voltage, for example to control the volume (loud- ness) in radio or TV.

Presets are miniature versions of standard variable resistors. They are designed to be mount- ed directly onto circuit boards and adjusted only when the circuit is built. For example, they may be used to set the frequency of an alarm tone or the sensitivity of a light-sensitive circuit. A small screwdriver or similar tool is usually required to adjust presets.