In simple language, a capacitor is a component that conducts energy in an electric field between two charged "plates" for a short period of time. The electric charge is then used or dissipated at an appropriate time. The capacitor essentially works along the same lines as the battery you might find in a flashlight, but with a few
minor differences.
Though any two conductors separated by an insulator have a capacitance; but a system of two or more conductors duel separated by an insulator when given the shape of a component to present a definite amount of capacitance is called a capacitor.
A capacitor is also a very useful component of electronic circuits like inductors and resistors. It is used in amplifiers, oscillators, filter circuits and many other types of electronics circuits.
Classification of capacitors
Fixed capacitor: A capacitor having a fixed capacitance value is called a fixed capacitor. Its capacity can't be changed easily, i.e. paper, mica, electrolyte etc.
Adjustable capacitor: A capacitor whose value can easily be changed with the help of a screw driver is called an adjustable capacitor. Its capacitance can be set at
the desired value, i.e. trimmer, padder etc.
Variable capacitor: A capacitor whose value can easily be set with the help of its shaft between its minimum and maximum values is called a variable capacitor, i.e. gang capacitor.
Fixed capacitors
1. Paper capacitors:
This type of capacitor is made by two long aluminium foils duel separated by wax paper strips and rolled together to take a cylindrical shape. A connecting is joined to the each aluminium foil and the capacitor is with a suitable resin binder.
Value is 0.0001 µF to 2.0 µF.
Working voltage is up to 2000 volts D.C.
Only fixed capacitors are made.
Small in size and cheap in cost.
Unsuitable for high frequency circuits.
2. Mica capacitors:
This type of capacitor is made by two brass or alloy metal plates separated by a thin sheet of mica. For making a capacitor of high capacitance value, a number of two plates systems are joined together. The whole combination is covered with a suitable resin binder to take cuboids shape.
Characteristics:
Value is 5 pF to 0.05 µF.
Working voltage is 500 to 2500 volts.
Fixed and adjustable capacitors are made.
Suitable for high frequency. Unaffected from dampness. Capacitance value remains almost stable.
3. Polystre or styroflex capacitors:
This type of capacitor is made by same as paper capacitor. But instead of paper dielectric a very fine polythene sheet is used as dielectric.
Characteristics:
Value is 2.5 pF to 0.05 µF.
Working voltage is up to 400 volts D.C.
Only fixed capacitors are made.
Size is smaller than paper capacitors.
Suitable for high frequency circuits and miniature equipments.
4. Ceramic capacitors:
This type of capacitor is made in tubular, disc or pin –up shape. It employs a ceramic dielectric which is a compound of titanium, barium, magnesium and strontium. This compound has a dielectric constant of up to 6000. Aluminium, tin or silver is used for making conductor plates in these capacitors.
Characteristics:
Value is 2.5pF to 0.22µF.
Working voltage is 50 to 1500 volts D.C.
Only fixed capacitors are made.
It can be made very small in size.
Suitable for high frequency. It can be designed to have a positive, zero or negative temperature coefficient. It has a long working life.
5. Electrolytic capacitors:
This type of capacitor consists of an electrolyte between two sets of plates called positive and negative that is why it is known as electrolytic capacitor. Like a secondary cell when an electrolytic capacitor is connected across D.C., a chemical action takes place and an insulating layer is formed on the positive plates. The layer so formed acts as a dielectric. There are two types of electrolytic capacitors which are as follows:
Wet type:
This type of capacitor consists of a cylindrical aluminium pot which is filled with a solution of boric acid and sodium borate. (Solution of ammonium borate, sodium phosphate, aluminium borate etc also may be used). A group of plates is placed in the solution which may be of many diversified shapes. When the plate group and the pot is connected to D.C. positive and negative respectively, the electrolysis action is started. As a result of said action, a very thin layer of aluminium oxide is formed on the positive plates which act as dielectric.
The above explain action is called ‘forming’ and it is performed in factories during manufacturing.
Dry type:
In a dry type electrolytic capacitor the solution is replaced by a paste. Its construction process is similar to that used for paper capacitor. Long and thin aluminium foil separated by paper sheets embedded in the electrolytic paste is rolled to take a cylindrical shape and roll is fitted in aluminium. There is no possibility of
leakage in a dry electrolytic capacitor; hence these capacitors are used commonly in electronic circuits.
Characteristics:
Value is 1µF to 2000µF.
Working voltage is up to 450 volts D.C.
Only fixed capacitors are made.
Small size in consideration to their high capacity (it is due to very thin layer of dielectric).Suitable for filter circuits.
6. Oil dielectric capacitors:
This type of capacitors consists of brass or iron conductor plates separated by oil dielectric. A mineral oil or hydrogenated caster oil is suitable for the purpose. These capacitors are made in cuboid shape.
Characteristics:
Value is 0.001µF to 0.1µF.
Working voltage is up to 25000 volts D.C.
Only fixed capacitors are made.
These capacitors have a long life. Suitable for transmitters.
7. Air dielectric capacitors:
In this type of capacitors, air is used as dielectric between conductor’s plates. Usually, these capacitors are made in variable type.
Characteristics:
Value is 5 pF to 600 pF.
Working voltage is up to 500 volts D.C.
Usually variable type capacitors are made.
These capacitors are made in small and large both sizes.
Suitable for tuning circuits.
Adjustable capacitors:
1. Trimmer:
Its capacitance value is kept between 3 to 30 pF or 4 to 70pF. Its types are as follows:
Parallel plate type:
It consists of two alloy metal plates placed parallel to each other. One plate is fitted on Bakelite or a porcelain base and the other one is a tension plate which is fitted in such a way that the distance between the two plates can be adjusted by a screw. The variation in distance between the two plate varies the capacitance value of the trimmer. A mica sheet works as dielectric between the two plates.
Cup type:
It consists of two aluminium cups having different diameters. One cup is kept stable while the other one inverted over the first can be adjusted to desired position with the help of a screw. The variation of distance between the two cups varies the capacitance value of the trimmer. Air works as dielectric between the two cup.
Wire type:
It consists of a thick enameled copper wire erected on the chassis by soldering its one end and a thin enameled copper wire wound over the thick one. The stray capacitance which exists between any two turns of the thin wire is utilized in it. The value of its capacitance can be varied by changing the distance between the turns of thin wire with the help of an insulated strip.
Disc type:
It consists of two semi-circular discs of brass. One disc is kept fixed and the other one can be rotated with the help of a screw over the first one. A mica sheet or polythene a sheet may be used as dielectric between the two discs. The value of its capacitance can be varied by changing the effective area between the two discs.
2. Padder:
It is also an adjustable capacitor whose capacitance value can be adjusted between 400 to 600 pF with the help of a screw. It consists of two or more plate couples. The value of its capacitance can be varied by changing the distance between the plates. Mica sheets are used as dielectric between the plates.
Trimmers and padders are used for frequency setting purpose in radio receivers.
Variable capacitors:
A radio receiver consists of more than one tuning circuits which require more than one variable capacitors controlled by a single shaft. These capacitors are called ‘gang capacitors’. A gang capacitor consists of two sets of plates –one is known as stator and the other as rotor. The rotor plates group can be rotated through an angle of 180º. The value of its capacitance can be varied by changing the effective area between the two plate groups. Its capacitance value is kept between 30pF to 600pF. For a valve type radio receiver 135pF to 500pF and for a transistorized radio receiver 90pF to 210pF capacitors are used. Air works as dielectric between the two plate groups.
minor differences.
Though any two conductors separated by an insulator have a capacitance; but a system of two or more conductors duel separated by an insulator when given the shape of a component to present a definite amount of capacitance is called a capacitor.
A capacitor is also a very useful component of electronic circuits like inductors and resistors. It is used in amplifiers, oscillators, filter circuits and many other types of electronics circuits.
Classification of capacitors
Fixed capacitor: A capacitor having a fixed capacitance value is called a fixed capacitor. Its capacity can't be changed easily, i.e. paper, mica, electrolyte etc.
Adjustable capacitor: A capacitor whose value can easily be changed with the help of a screw driver is called an adjustable capacitor. Its capacitance can be set at
the desired value, i.e. trimmer, padder etc.
Variable capacitor: A capacitor whose value can easily be set with the help of its shaft between its minimum and maximum values is called a variable capacitor, i.e. gang capacitor.
Fixed capacitors
1. Paper capacitors:
This type of capacitor is made by two long aluminium foils duel separated by wax paper strips and rolled together to take a cylindrical shape. A connecting is joined to the each aluminium foil and the capacitor is with a suitable resin binder.
 |
| Paper Capacitor |
Characteristics:
Working voltage is up to 2000 volts D.C.
Only fixed capacitors are made.
Small in size and cheap in cost.
Unsuitable for high frequency circuits.
2. Mica capacitors:
This type of capacitor is made by two brass or alloy metal plates separated by a thin sheet of mica. For making a capacitor of high capacitance value, a number of two plates systems are joined together. The whole combination is covered with a suitable resin binder to take cuboids shape.
 |
| Mica Capacitor |
Characteristics:
Value is 5 pF to 0.05 µF.
Working voltage is 500 to 2500 volts.
Fixed and adjustable capacitors are made.
Suitable for high frequency. Unaffected from dampness. Capacitance value remains almost stable.
3. Polystre or styroflex capacitors:
 |
| Polystre Capacitor |
This type of capacitor is made by same as paper capacitor. But instead of paper dielectric a very fine polythene sheet is used as dielectric.
Characteristics:
Value is 2.5 pF to 0.05 µF.
Working voltage is up to 400 volts D.C.
Only fixed capacitors are made.
Size is smaller than paper capacitors.
Suitable for high frequency circuits and miniature equipments.
4. Ceramic capacitors:
 |
| Ceramic Capacitor |
This type of capacitor is made in tubular, disc or pin –up shape. It employs a ceramic dielectric which is a compound of titanium, barium, magnesium and strontium. This compound has a dielectric constant of up to 6000. Aluminium, tin or silver is used for making conductor plates in these capacitors.
Characteristics:
Value is 2.5pF to 0.22µF.
Working voltage is 50 to 1500 volts D.C.
Only fixed capacitors are made.
It can be made very small in size.
Suitable for high frequency. It can be designed to have a positive, zero or negative temperature coefficient. It has a long working life.
5. Electrolytic capacitors:
 |
| Electrolytic Capacitor |
This type of capacitor consists of an electrolyte between two sets of plates called positive and negative that is why it is known as electrolytic capacitor. Like a secondary cell when an electrolytic capacitor is connected across D.C., a chemical action takes place and an insulating layer is formed on the positive plates. The layer so formed acts as a dielectric. There are two types of electrolytic capacitors which are as follows:
Wet type:
This type of capacitor consists of a cylindrical aluminium pot which is filled with a solution of boric acid and sodium borate. (Solution of ammonium borate, sodium phosphate, aluminium borate etc also may be used). A group of plates is placed in the solution which may be of many diversified shapes. When the plate group and the pot is connected to D.C. positive and negative respectively, the electrolysis action is started. As a result of said action, a very thin layer of aluminium oxide is formed on the positive plates which act as dielectric.
The above explain action is called ‘forming’ and it is performed in factories during manufacturing.
Dry type:
In a dry type electrolytic capacitor the solution is replaced by a paste. Its construction process is similar to that used for paper capacitor. Long and thin aluminium foil separated by paper sheets embedded in the electrolytic paste is rolled to take a cylindrical shape and roll is fitted in aluminium. There is no possibility of
leakage in a dry electrolytic capacitor; hence these capacitors are used commonly in electronic circuits.
Characteristics:
Value is 1µF to 2000µF.
Working voltage is up to 450 volts D.C.
Only fixed capacitors are made.
Small size in consideration to their high capacity (it is due to very thin layer of dielectric).Suitable for filter circuits.
6. Oil dielectric capacitors:
 |
| Oil Dielectric Capacitor |
This type of capacitors consists of brass or iron conductor plates separated by oil dielectric. A mineral oil or hydrogenated caster oil is suitable for the purpose. These capacitors are made in cuboid shape.
Characteristics:
Value is 0.001µF to 0.1µF.
Working voltage is up to 25000 volts D.C.
Only fixed capacitors are made.
These capacitors have a long life. Suitable for transmitters.
7. Air dielectric capacitors:
 |
| Air Dielectric Capacitor |
In this type of capacitors, air is used as dielectric between conductor’s plates. Usually, these capacitors are made in variable type.
Characteristics:
Value is 5 pF to 600 pF.
Working voltage is up to 500 volts D.C.
Usually variable type capacitors are made.
These capacitors are made in small and large both sizes.
Suitable for tuning circuits.
Adjustable capacitors:
1. Trimmer:
 |
| Trimmer |
Its capacitance value is kept between 3 to 30 pF or 4 to 70pF. Its types are as follows:
Parallel plate type:
 |
| Parallel Plate Capacitor |
It consists of two alloy metal plates placed parallel to each other. One plate is fitted on Bakelite or a porcelain base and the other one is a tension plate which is fitted in such a way that the distance between the two plates can be adjusted by a screw. The variation in distance between the two plate varies the capacitance value of the trimmer. A mica sheet works as dielectric between the two plates.
Cup type:
It consists of two aluminium cups having different diameters. One cup is kept stable while the other one inverted over the first can be adjusted to desired position with the help of a screw. The variation of distance between the two cups varies the capacitance value of the trimmer. Air works as dielectric between the two cup.
Wire type:
It consists of a thick enameled copper wire erected on the chassis by soldering its one end and a thin enameled copper wire wound over the thick one. The stray capacitance which exists between any two turns of the thin wire is utilized in it. The value of its capacitance can be varied by changing the distance between the turns of thin wire with the help of an insulated strip.
Disc type:
It consists of two semi-circular discs of brass. One disc is kept fixed and the other one can be rotated with the help of a screw over the first one. A mica sheet or polythene a sheet may be used as dielectric between the two discs. The value of its capacitance can be varied by changing the effective area between the two discs.
2. Padder:
 |
| Padder |
It is also an adjustable capacitor whose capacitance value can be adjusted between 400 to 600 pF with the help of a screw. It consists of two or more plate couples. The value of its capacitance can be varied by changing the distance between the plates. Mica sheets are used as dielectric between the plates.
Trimmers and padders are used for frequency setting purpose in radio receivers.
Variable capacitors:
 |
| Variable Capacitor |
A radio receiver consists of more than one tuning circuits which require more than one variable capacitors controlled by a single shaft. These capacitors are called ‘gang capacitors’. A gang capacitor consists of two sets of plates –one is known as stator and the other as rotor. The rotor plates group can be rotated through an angle of 180º. The value of its capacitance can be varied by changing the effective area between the two plate groups. Its capacitance value is kept between 30pF to 600pF. For a valve type radio receiver 135pF to 500pF and for a transistorized radio receiver 90pF to 210pF capacitors are used. Air works as dielectric between the two plate groups.
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