A capacitor (originally known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. OR capacitor or condenser, device for the storage of electric charge.
Simple capacitors consist of two plates made of an electrically conducting material (e.g., a metal) and separated by a non-conducting material or dielectric (e.g., glass, paraffin, mica, oil, paper, tantalum, or air).
If an electrical potential (voltage) is applied to the plates of a capacitor (e.g., by connecting one plate to the positive and the other to the negative terminal of a storage battery), the plates will become charged, one positively and one negatively.
If the externally applied voltage is then removed, the plates of the capacitor remain charged, and the presence of the electric charge induces an electrical potential between the plates.
It is given by,
C: Capacitance of capacitor in farad
A: Area of any one plate in m2
D: Distance between two plates in m
ε: Permittivity of material = ε0εr
ε0: Absolute permittivity = 8.854X10-12 farad/meter
εr: Relative permittivity
The capacity of the device for storing electric charge (i.e., its capacitance) can be increased by increasing the area of the plates, by decreasing their separation, or by changing the dielectric. The dielectric constant of a particular dielectric is the measure of the dielectric’s unit capacitance.
Classification of capacitor
The capacitor may be classified in many ways as follows.
On the basis of nature of value
- Fixed capacitor
- Variable capacitor
On the basis of dielectric material used
- Paper capacitor
- Mica capacitor
- Ceramic capacitor
- Plastic capacitor
- Air capacitor
- Glass capacitor
- Electrolytic capacitor
- Vitreous enameled capacitor
Dielectric Materials Used in Capacitor
- Waxed paper
- Working voltage: It is defined as the maximum voltage at which the capacitor can operate without failure.
- Capacitive reactance: The resistance offered by the capacitor to the flow of current is called capacitive reactance. It is denoted by XC. It is measured in ohm(Ω). It is given by
- Frequency characteristic: It is the graph which is plotted between impedance and applied frequency is known as frequency characteristic. In a capacitor as the applied frequency increases the impedance decreases.
Fixed capacitors: Specifications and Applications
Impregnated Paper Capacitor
- Range of values : 0.001 µF to 1 µF
- Tolerance : ±15%
- Voltage ratings : 400V, 600 V, 1200V, 1800 V
- Power factor at 1KHz : 0.005 to0.01
- Temperature coefficient : 100 to 200 ppm/C
- They are used as RF bypass capacitors and coupling capacitors.
Metalized Paper Capacitor
- Range of values : 0.001 µF to 1 µF
- Tolerance : ±25%
- Voltage ratings : 1500 V
- Power factor at 1KHz : 0.02
- Temperature coefficient : 150 to 200 ppm/C
- They are used as decoupling capacitors.
- Range of values : 50pF to 500 pF
- Voltage ratings : 2 KV
- Operating temperature : -55 C to 125C
- It is widely used in radio and telecommunication.
- It is used in filter circuit and tuning circuit.
- It is used in AC and DC applications.
- Range of values : 1pF to 1µF
- Voltage ratings : 500 V dc
- Operating temperature : 150 C
- It is used in radio and telecommunication.
- It can be used in computers, industrial equipments.
- It can be used as a coupling capacitor.
- Range of values : 150 pF to 10000pF
- Voltage ratings : 300 V to 500 V dc
- Operating temperature : -55 C to +200 C
- It is used where high reliability is required.
- It is used in medium power transmitter.
- Range of values : upto 1µF
- Voltage ratings : 100 V dc
- Operating temperature : 250 C.
- It is used in tuned circuit.
- It is used in digital equipment.
- It is used in long time constant circuit.