Capacitors

A capacitor is one of the main elements of acircuit. It is used Ц store electric energy. A capacitor stores electric energy provided that j voltage source is applied to it.

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Fig. 9

The main parts of a capacitor are metal plates and insulators. ТЫ function of insulators is to isolate the metal plates and in this way t<J prevent a short.

In the diagram one can see two common types of capacitors in usJ nowadays: a fixed capacitor and a variable one. The plates of afixeJ capacitor cannot be moved; for this reason its capacity does not change The plates of a variable capacitor move; its capacity changes. ТЫ greater the distance between the plates, the less is the capacity of a ca[ pacitor. Variable capacitors are commonly used by radiomen; theil function is to vary the frequency in the circuit. Fixed capacitors ar^ used in telephone and radio work.

Fixed capacitors have insulators produced of paper, ceramics an^ other materials; variable capacitors have air insulators. Paper capacitors are commonly used in radio and electronics; their advantage is theij high capacity: it may be higher than 1,000 picofarad.

Besides, electrolyte capacitors are highly in use. They also have avery high capacity: it varies from 0.5 to 2,000 microfarad. Their disadf

2. The main parts of a capacitor are

3.The function of insulators is

4. The capacity of a capacitor de­pends on

5. The capacity of a fixed capacitor

6. The plates of a variable capaci­tor

7. In order to charge a capacitor a voltage source is applied

8. The greater the distance between the plates,

a) insulators only.

b) metal plates only.

c) metal plates and insulators be­tween them.

a) to store energy.

b) to isolate the metal plates.

c) to prevent a short between the metal plates.

a) the size of the plates.

b) the distance between the plates.

c) the material of the insulators.

a) is constant.

b) is varied.

a) can be moved.

b) cannot be moved.

a) to the metal plates.

b) to the insulators.

a) the greater is the capacity of a capacitor.

b) the less is the capacity.

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a) air insulators.

b) paper insulators.

c) ceramic insulators.

d) a very low capacity.

e) a very high capacity.

f) it operates.

g) it stops operating.

5. Complete these sentences using while. Follow the model on page 13:

1. The plates of a fixedcapacitor cannotbe moved to vary the capacity

2. The capacity of a variablecapacitor is varied..........

3. Electrolytecapacitors changetheir capacity when the temperaturj changes

4. The lessthe distance between the plates, the greateris the capacity .

5. When a capacitor has notrouble it storesenergy..........

6. Pairwork. Put these questions to your groupmate and ask him/her tc
answer them.

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 does the capacity of a capacitor depend on?

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 о plates?

8. What type of insulators have variable capacitors?

9. What should be done in case a capacitor has a trouble?

7. Solve theseproblems:

Draw a diagram of a circuit consisting of two resistors and two capacj tors connected in parallel. A battery of four cells is applied to the circdj Two ammeters are used: one is connected to the main line, the other - to parallel branch. What is the function of each element? In what way can otj increase the value of resistance in the circuit?

Suppose one of the branches stops operating. What does it result from^|

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a) Cover the right column and read the English words. Translate them into Russian and check your translation.

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