Capacitors

The plates of a variable capacitor move; its capacity changes. The greater the distance between the plates, the less is the capacity of a capacitor. Variable capacitors are commonly used by radiomen; their function is to vary the frequency in the circuit. Fixed capacitors are used in telephone and radio work. Fixed capacitors have insulators produced of paper, ceramics and other materials; variable capacitors have air insulators. Paper capacitors
are commonly used in radio and electronics; their advantage is their high capacity: it may be higher than 1,000 picofarad. Besides, electrolyte capacitors are highly in use. They also have a
very high capacity: it varies from 0. 5 to 2,000 microfarad. Their disadvantage is that they change their capacity when the temperature changes. They can operate without a change only at temperatures notlower than -40 C. ,Common troubles in capacitors are an open and a short. A capacitor stops operating and does not store energy in case it has a trouble. A capacitor with a trouble should be substituted by a new one.
Complete these sentences using the correct variant
1. A capacitor is used
a) to supply voltage.
b) to increase the voltage output.
c) to store energy.
2. The main parts of a capacitor are
a) insulators only.
b) metal plates only.
c) metal plates and insulators between
them.
3. The function of insulators is
a) to store energy.
b) to isolate the metal plates.
c) to prevent a short between the
metal plates
4. The capacity of a capacitor depends
on
a) the size of the plates.
b) the distance between the plates.
c) the material of the insulators.
5. The capacity of a fixed capacitor
a) is constant,
b) is varied.
6. The