capacitor
Types Of Capacitors and Their Uses
According to control, there are two main types of capacitor:
1. Fixed Capacitors
2. Variable Capacitors
1. Fixed Capacitors- A capacitor with a fixed value of capacitance is called a fixed capacitor. it can be classified further according to the dielectric used in it as follows:
(a) Paper capacitor
(b) Mica capacitor
(c) Electrolytic capacitor
(d) Ceramic capacitor
(a) Paper capacitor- It consists of two thin tin or aluminium foils placed alternately between three wax-paper foils. all the foils are rolled to take a cylindrical shape in such a way, that one conductor foil remains insulated from the other. the roll is housed in aluminium cylindrical container or is coveted with a suitable bitumen compound, while two connecting leads, one from each conductor foil are taken out as
(b) Mica capacitor- It consists of many thin conductor plates separated by mica sheets and placed alternately to taken the shape of a cuboid. one connecting lead is connected to plates 1,2,3... and the other to 2,4,6... the whole assembly is coveted with a suitable bitumen compound
the capacitance value of paper capacitors is usually between 0.001µF to µF; and of mica capacitors is usually between 5 pF to 0.01 µF. both types of capacitors are used in different electrical and and electronic equipments.
(c) Electrolytic capacitor- It consists of a set of aluminium plates immersed in ammonium borate or sodium phosphate solution filled in an aluminum can. these capacitors are used in d.c.circuit only, because when the plates are kept at positive and the can at negative potentials then a film of aluminium oxide is formed on the plates, which acts as a dielectric between the plates and the solution. the specialties of an electrolytic capacitor are its high capacitance value, ranging from 1 to 1000 µF and its small size.
(d) Ceramic capacitor- It consists of two aluminium plates separated by a layer of ceramic compound. its size is smallest amongst all other types of capacitors and its value ranges from 5 pF to 0.1 µF. It is used in electronic equipments.
2. Variable Capacitor- A capacitor whose capacitance value can be varied between a specified rangs as required, is called a variable capacitor. it consists of two sets of aluminium plates known as the rotor the stator as air is used as dielectric between the plates. when the rotor plates are completely covered stator plates then its capacitance is maximum; and when rotor plates are out of the stator plates then the capacitance is minimum. it is used in radio receivers, transmitters etc. and is commonly known as an air-gang capacitor or gang capacitor.
Electrical Uses Of Capacitors
1. In Single Phase Motors- A capacitor is used to split the single phase into two parts and thus to increase the torque of a single phase motor, ceiling fan of a table fan.
2. In Fluorescent Tubes - A capacitor is used in the starter of a fluorescent tube to start it and in parallel of the tube to eliminate any electrical interference which may be caused be the tube in a nearby radio receiver.
3. In Inductive Circuits- A capacitor is used in inductive circuit to improve the power factor of the circuit .
4. In Distributors- A capacitor used to reduce sparking in the distribution of auto vehicles e.g., bus, car, motor cycle etc.
Dielectric Strength
The amount of maximum kilovolts per millimetre thickness of a dielectric, which it can withstand safely, is called its dielectric strength in other words the ability of a dielectric material which resists its insulation break down in the presence of a high voltage across it is called its dielectric strength or dielectric break down voltage. its value depends upon the following factors.
Capacitor and its Principle
A system of two conductors separated by a dielectric is called a capacitor or a condenser its function is to store the electrical energy and to release it as and when required. tin and aluminium are the common conductors and mica, oil, paper, ceramic, polyester etc. are the common insulators which are used in the construction of capacitors. the conductor plates are usually kept parallel, whereas the dielectric keeps the conductor plates separated from each other.
A simple capacitor it is connected to a battery through a switch S.the plate A is connected to the positive terminal and the plate B to the negative terminal of the battery.
When the switch is put 'ON' then a momentary current flows in the circuit and the plate B negative. the negative terminal of the battery supplies electrons to the plate B of the capacitor and makes it negative changed the negative charge of the plate B repels some of the electrons from plate A due to electrostatic induction and makes it positive with respect to plate B the electrons repelled the plate A are attracted by the positive terminal of the battery in this way the capacitor is charged due to a momentary flow of electrons in the circuit from negative to positive terminal of battery.
Capacitors in Series
When two or more capacitor are connected from and to and then the connection is called a series connection in this circuit each capacitor holds the same charged but the p.d. across each capacitor is different. if three capacitor C1, C2, and C3
are connected in series as the voltage applied is V volts and the p.ds. across
the capacitors are V1, V2, and V3 then V= V1+V2+V3
According to control, there are two main types of capacitor:
1. Fixed Capacitors
2. Variable Capacitors
1. Fixed Capacitors- A capacitor with a fixed value of capacitance is called a fixed capacitor. it can be classified further according to the dielectric used in it as follows:
(a) Paper capacitor
(b) Mica capacitor
(c) Electrolytic capacitor
(d) Ceramic capacitor
(a) Paper capacitor- It consists of two thin tin or aluminium foils placed alternately between three wax-paper foils. all the foils are rolled to take a cylindrical shape in such a way, that one conductor foil remains insulated from the other. the roll is housed in aluminium cylindrical container or is coveted with a suitable bitumen compound, while two connecting leads, one from each conductor foil are taken out as
Paper capacitor
(b) Mica capacitor- It consists of many thin conductor plates separated by mica sheets and placed alternately to taken the shape of a cuboid. one connecting lead is connected to plates 1,2,3... and the other to 2,4,6... the whole assembly is coveted with a suitable bitumen compound
the capacitance value of paper capacitors is usually between 0.001µF to µF; and of mica capacitors is usually between 5 pF to 0.01 µF. both types of capacitors are used in different electrical and and electronic equipments.
Mica capacitor
(c) Electrolytic capacitor- It consists of a set of aluminium plates immersed in ammonium borate or sodium phosphate solution filled in an aluminum can. these capacitors are used in d.c.circuit only, because when the plates are kept at positive and the can at negative potentials then a film of aluminium oxide is formed on the plates, which acts as a dielectric between the plates and the solution. the specialties of an electrolytic capacitor are its high capacitance value, ranging from 1 to 1000 µF and its small size.
(d) Ceramic capacitor- It consists of two aluminium plates separated by a layer of ceramic compound. its size is smallest amongst all other types of capacitors and its value ranges from 5 pF to 0.1 µF. It is used in electronic equipments.
2. Variable Capacitor- A capacitor whose capacitance value can be varied between a specified rangs as required, is called a variable capacitor. it consists of two sets of aluminium plates known as the rotor the stator as air is used as dielectric between the plates. when the rotor plates are completely covered stator plates then its capacitance is maximum; and when rotor plates are out of the stator plates then the capacitance is minimum. it is used in radio receivers, transmitters etc. and is commonly known as an air-gang capacitor or gang capacitor.
Variable Capacitor
Electrical Uses Of Capacitors
1. In Single Phase Motors- A capacitor is used to split the single phase into two parts and thus to increase the torque of a single phase motor, ceiling fan of a table fan.
2. In Fluorescent Tubes - A capacitor is used in the starter of a fluorescent tube to start it and in parallel of the tube to eliminate any electrical interference which may be caused be the tube in a nearby radio receiver.
3. In Inductive Circuits- A capacitor is used in inductive circuit to improve the power factor of the circuit .
4. In Distributors- A capacitor used to reduce sparking in the distribution of auto vehicles e.g., bus, car, motor cycle etc.
Table For Dielectric Constants
|
Dielectric Material
|
Value of €r
|
Dielectric Material
|
Value of €r
|
|
Air
Ebonite
Petroleum
Insulating
Paraffin Wax
|
1
2-3
2
2.3
2.3
|
India rubber
Gutta Percha
Shellac
Mica
Glass
|
2.5
2.5-2.96
2.96-3.75
5-8
6-9
|
Table For Dielectric Strength Of Constants
|
Dielectric Material
|
Dielectric Strength kV/mm
|
Dielectric Constant
€r
|
|
Air
Bakelite
Ebonite
Fiber
Glass
India Rubber
Mica
Micanite
Paper
Porcelain
Shellac
Transformer Oil
|
3
17-21
30-40
5
5-12
30-50
20-40
20-40
1-10
8-12
3
30-50
|
1
5-6
2-3
4-6
6-9
2.5
5-8
6-8
2
4-7
2.95-3.75
2.5
|
Simple Capacitor Circuit
Capacitors in Series
Capacitors in Parallel
When two or more capacitor are connected in such a way that their positive plate are joined at one point and the negative plates at the other then the connection is called a parallel connection in this connection the p.d. of each capacitor remains the same but the charge stored in each capacitor is different.
Capacitors in Parallel
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