Voltage source is applied b) to the insulator.

6. The greater the distance between a) the greater is the capacity of a the plates, capacitor.

b) the less is the capacity.

9. Variable capacitors have

10. Electrolyte capacitors have

a) air insulator.

6) paper insulator.

c) cemmic insulator.

B) a very low capacity.

b) a very high capacity.

11. In case a capacitor has a trouble a) it operates.

b) it stops operating.

Complete these sentences using wh‘tie. follow the mo6el on page 13:

1. The plates of a fixed capacitor cennot be moved to vary the capacity ..

2. The capacity of a verleblc capacitor is verlcd ..

3. Electrolyte capacitors change their capacity when the temperature

changes ..

4. The less the distance between the plates, the greater is the capacity .:.

5. When a capacitor has no trouble it stores energy ..

^{Peir work Put these questions to your groupmatc and ask hiai/hcr to} enswcr them.

l. What is a capacitor used for?

2. What are the main parts of a capacitor?

3. What is the function of insulators?

4. What does the capacity of a capacitor depend on7

5. What is the difference between a fixed capacitor and a variable one?

6. What should be done in order to change a capacitor?

7. What is the relation between the value of capacity and the distance of

plates?

2. What type of insulator have variable capacitor?

3. What should be done in case a capacitor has a troubled

7. Solve these problems:

Draw a diagram of a circuit consisting of two resistor and two capaci- tor connected in parallel. A battery of four cells is applied to the circuit. Two anunctcrs arc used: one is connected to the main line, the other — to a parallel branch. What is the function of each element? In what w8y can one increase the value of resistance in the circuit7

Suppose one of the branches stops operating. What does it result bom7

1. a) Cover tbc right columa and read tbc Eaglisb words. Translate

tbcai lato Russias and cbcck your trsaslettoa.

b) Cover tbc IcA columa aod translate tbc Russian words back iato

English.

cheap

make smb (smth)

do smth

nemensiR

thus
difficulty
'rubber
to decrease increase	[dI1‹ri:s] ['iijkri:sl	eHhmBrs yaeniiscioic

2. Rcnd the words end put down thelr Russlen cqulvalents:

['daiaprnml	diagram
[J‹ouiIiJantJ	coefficient
[1xgk]an]	flinction
[trxns10:rna]	transfonncr
[trnnsIa:l	to transfer

3. Form adverbs. Follow the aiodcl•

Model. wide - widely

cheap - high -

4. PutdowetboRo**!*efor:

load resistance

wire conductors

silver wire conductors

temperature 'dccrc05c

temperature 'increase

5. Translate into Russian. Mind since.

I . Copper conductors are widely used xiiice they are much cheaper than silver ones.

2. A minimum voltage drop is produced in copper wire conductors since they have a low resistance.

3. A bulb connected to an open circuit does not light since an open circuit

has no current.

Conductors and Insulators

Conductors are materials having a low resistance so that current easily 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

silver. 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 re- sistance a minimum voltage drop is produced in them. Thus, all of the applied voltage 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 metals have a positive temperature coefficient of resistance while carbon has a negative temperature coefficient. The smaller is the tem- perature 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. Cur-

rent passes through insulator with great difficulty.

The most common insulators are air, paper, rubber, plastics.

Any insulator can conduct current when a high enough voltage is applied to it. Currents of great value must be applied to insulator in or- der 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 the two main functions:

1. to isolate conducting wires and thus to prevent a short between

them and

2. to store electric charge when a voltage source is applied.

6. Find answers to these questions tn the text above:

1. What materials arc called conductor?

2. What is the advantage of copper compared with silver?

3. What is the most common fiinction of wire conductor?

4. Why is a minimum voltage drop produced in copper conductor?

5. What is the relation between the value of resistance and the temperature

in carbon?

6. What materials are called insulator?

7. What are the most common insulatom7

8. What are the two main fiinctions of insulator?

7. Complete the sentences using the correct variant:

l. Insulator are materials having a) low resistance.

6) high resistance.