what is capacitors? symbol, definition, top most 10 types, useful important facts

capacitor definition-

A device made by placing a dielectric medium (bad conductor) between two metallic conductor plates is called a capacitor.

A capacitor is a device that opposes changes in voltage.

Mica, ebonite, air etc. are used as dielectric medium (bad conductor) in capacitor.

Metals like tin, aluminium etc. are used for conductor plates in capacitors.

The temperature coefficient of the capacitor plates is generally positive.

capacitor symbol

Working of Capacitor

In the natural state, both plates of a capacitor have an equal number of free electrons.
When the capacitor is connected to a voltage source, electrons are removed from plate A, and an equal number are deposited on plate B. As plate A loses electrons and plate B gains electrons, plate a becomes positive Concerning plate B.

During this charging process, electrons flow only through the connecting leads. No electrons flow through the dielectric of the capacitor because it is an insulator. The movement of electrons ceases when the voltage across the capacitor equal the source voltage. A charged capacitor can act as a temporary battery.

Basic Construction:

A capacitor is an electrical device used to store electrical charge and energy in an electric field. It is made up of two parallel conductive plates that are separated by a non-conductive material known as a dielectric.

Types of Capacitors or capacitor types

Capacitors are mainly divided into two types-

1. Based on work
2. Based on the electrolyte material

Based on work

there are three Types capacitors

• constant value capacitor
• Time adjusted value capacitor
• variable value capacitor

constant value capacitor

Capacitors whose value cannot be changed later are called fixed capacitors. The value is called capacitor.

They are used as capacitors for domestic fans and motors etc.

Example- Paper capacitor, Mica capacitor, Ceramic capacitor

Time adjusted value capacitor

Those capacitors whose value can be changed by rotating the patch are called adjustable value capacitors.

Example- trimmer and padder capacitors

variable value capacitor

Those capacitors whose value can be changed within a limit are called variable value capacitors.

They are used to change the frequency in devices like radio etc. Example- Gang capacitor.

Based on the electrolyte material

• paper capacitor
• polyester capacitor
• ceramic capacitor
• mica capacitor
• Electrolytic Capacitor

paper capacitor

quality/characteristic

• Capacitance .0005 µF to 10 µF
• Dielectric constant (2-6)
• Voltage rating (100-1500) V
• Corrosion Resistance 100 μΩ
• Tolerance ±10%
• Small in size and useful in AC and DC
• Used in high voltage and high current applications
  

ceramic capacitor

quality/characteristic

• Capacitors from 3 pF to 2 µF
• dielectric constant 80-110
• Voltage rating (3-6000) V
• Erosion resistance (1000 m2) Very high
• Tolerance (±10 to ±15%)
• It is made in the shape of a disc or tube.
• Paper capacitors can be used on AC and DC equally.
• It can be used in high voltage and high current applications.
  
  

polyester capacitor

quality/characteristic

• Capacitance from 0.0005 µF to 10 µF
• dielectric constant up to 2-3
• Voltage rating range 2000 V
• Tolerance ±10%
• The insulation resistance of polyester capacitor is higher than that of paper capacitor
• Used in digital, tuned circuits.
  
  

mica capacitor

quality/characteristic

• The capacitance ranges from 1pF to 1 µF.
• Dielectric constant (3-8)
• Voltage rating (500 – 40 kV), high frequency
• Tolerance ±5%
• Leakage Resistance 1000 μΩ
• Power Factor (High)
• no effect of moisture
  
  

Electrolytic Capacitor

quality/characteristic

• Capacitance 1 µF to 1000 µF
• Dielectric constant (7-25)
• Voltage rating (2-500) V
• Tolerance ±10%
• Used in motor.
  
  
  

Energy stored in a capacitor:

When a capacitor is charged, Energy is stored in it. In the charging process, the
potential difference across the plates in proportion to the charge stored.

During this process, the capacitor draws some current from the source called charging
current and energy is stored in it. When the capacitor is fully charged, no more current is drawn from the source.

Some Important Dielectric Values-

Relationship between the voltage, capacitance and charge:

Capacitance: C = Q/V ; farad
Charge: Q = C.V ; Coulomb
Voltage: V = Q/C ; Volts

Capacitance-

The amount of charge that a capacitor can store per unit of voltage across its plates is
its capacitance. It is represented by C. The capacitance is a measure of a capacitor’s ability to store charge. Farad is the unit of capacitance.

One farad is the amount of capacitance when one coulomb of charge is stored with
one volt across the plates.

The property of storing charge in a capacitor is called capacitance. Capacitor’s capacitance = Q/ V

Therefore the unit of capacitance is farad or coulomb per volt.

Farad is a large unit. Hence, it is expressed in the following form-

So 1 micro farad (uF) = 10^-6F

1 nano farad (nF) = 10^-9F

1 picofarad (pF)= 10^-12F

Note- Energy in a capacitor is always in the form of electrostatic. We can also express the capacitance of a capacitor in the following manner.

Where,

• C = capacitance
• Electrostatic potential of the capacitor
• Relative electrostatic potential
• d = Distance between plates
• A = Plato’s area
• Electrical conductivity of air/vacuum is 8.85X10-12 F/m.
  

Factors affecting capacitance-

Capacitance depends on the following factors.

1. Capacitance is proportional to the area of ​​the plates.
2. Capacitance is inversely proportional to the distance between the plates.
3. Capacitance is proportional to the electrical conductivity of the medium.

4. Capacitance depends on temperature.
5. Capacitance depends on the resistance of the plates.
6. Capacitance depends on the number of plates. Cox (N-1)

Note – Capacitance does not depend on potential.

Capacitive Reactance-

The opposition offered by a capacitor to the flow of alternating current in a circuit is called linear impedance.

Its symbol is ‘ x_c‘ and unit is ohm.

Where – f = frequency (Hz)

Note– If DC current is used then the value of linear impedance becomes infinite.

Breakdown Potential of a Capacitor-

Its unit is volt per mm.

This breakdown strength of the dielectric of the capacitor depends on the thickness of the material.

Therefore, it can be said that breakdown potential is that value from where the dielectric medium stops functioning.

Dielectric Strength-

The property of a material which resists breakdown or which resists breakdown according to its strength without breaking is called dielectric strength.

Its unit is volt per unit thickness.

Dielectric Loss in Dielectric Material-

The thermal power emitted from a dielectric material placed in an electric field is called dielectric power losses.

When a dielectric material is kept in an electrostatic field, a leakage current starts flowing in it due to external influence or impurities.

Due to this, power losses in the form of heat start occurring in that material, which is called dielectric constant loss.

Some Important Conditions of Capacitor-

1. When the plates of the capacitor are in the same dielectric mean–

Therefore, it is clear that by inserting a dielectric medium between the plates of the capacitor, the value of the capacitance of the capacitor increases.

When a parallel capacitor has strips of different thickness and dielectric constant, then the value of the capacitance of the capacitor is-

When there is air medium in some part of the parallel plate capacitor and some part is some other medium, then the value of the capacitance of the capacitor-

When in the horizontal direction in the middle of a parallel plate capacitor, some part is air medium and some part is other medium–

Capacitance of a cylindrical capacitor

Capacitance of parallel conductors-

Consider three capacitors, C1, C2 and C3, are connected in parallel to a d.c supply of ‘V’ volts.

Let,
C = Equivalent capacitance of series combination
V = Voltage across each capacitor
Q1 = Charge stored by C1
Q2 = Charge stored by C2
Q3 = Charge stored by C3
In series circuit, QT = Q1 + Q2 + Q3

Where,
Q1 = C1V
Q2 = C2V
Q3 = C3V

Where C is the total equivalent circuit capacitance, then it stores the same charge (Q) when connected to the same voltage (V).
Then,
QT = C V ————– (3)
Substitute the value of equation
C V = C1V+C2V+C3V ————– (4)
Divide equation (4) by V :
C = C1+C2+C3
If ‘n’ number of capacitor in parallel:
C = C1+C2+..+Cn

Current in converted or multiplate transmitter or group capacitor

Note– In a plate capacitor, the negative plate is always one more than the positive plate for insulation protection. This type of capacitor is used in radios.

*exam useful important facts

A capacitor has an insulator medium between two conducting plates.

There is a relation (E = V/d) between the electric field intensity (E) between the conducting plates, the applied voltage (V) and the distance (d) between the plates.

The dissipation factor of a capacitor can be measured using a shearing breeche.

Elastance is the inverse of capacitance.

The capacity of the capacitor used in power factor improvement is expressed in VAR.

The appropriate place to place a capacitor is at the terminals of an inductive load.

The power factor of a pure leading capacitor circuit remains leading.

The power dissipated in a pure capacitor is zero.

The gang condenser used in radio is of air capacitor type.

The trimmer capacitor is a variable type of capacitor.

In a parallel anode capacitor, if the area of ​​each anode is doubled and the dielectric is halved, there is no change in capacitance.

The energy E stored in a capacitor is given by the formula ((CV²) CV²). 1

In a pure capacitor, the electric current is 90° ahead of the voltage.

Time constant (t) of resistance, capacitor circuit = RC

A capacitor always stores “energy” (electric field) in the form of charge.

The charge of a capacitor always remains constant in the “dielectric constant”.

FAQ-(what is capacitor)

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