What is Capacitor and advantages, disadvantages and Applications

 Capacitor

A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). The conductors can be thin films of metal, aluminum foil or disks, etc. The 'nonconducting' dielectric acts to increase the capacitor's charge capacity. A dielectric can be glass, ceramic, plastic film, air, paper, mica, etc. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, a capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates. When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge (+Q) to collect on one plate and negative charge (-Q) to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if an accelerating or alternating voltage is applied across the leads of the capacitor, a displacement current can flow.
An ideal capacitor is characterized by a single constant value for its capacitance. Capacitance is expressed as the ratio of the electric charge (Q) on each conductor to the potential difference (V) between them. The SI unit of capacitance is the farad (F), which is equal to one coulomb per volt (1 C/V). Typical capacitance values range from about 1 pF (10−12 F) to about 1 mF (10−3 F).
The capacitance is greater when there is a narrower separation between conductors and when the conductors have a larger surface area. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, known as the breakdown voltage. The conductors and leads introduce an undesired inductance and resistance. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems they stabilize voltage and power flow.

Introduction

A capacitor consists of two-terminal, it stores electrical power or energy in shape of an electrical field. As we discussed above capacitor has dielectric material among the electric plates this dielectric material do not allow direct current to pass instead it stores voltage in the shape of charge across plates of a capacitor. The metallic plates of a capacitor can be of any shape like circle, rectangle, square, or sphere, in which shape it to be made is depends on its use and at which voltage it has to be used. Whenever we use a capacitor in such circuitry which working on direct current insulating material stops movement of current but it stored charged on plates of a capacitor. But, when a capacitor is associated to an alternating current circuit, the movement of the current seems to permit easily through the capacitors with slight or no resistance. There are two main kinds of electrical charges first one is positive and the second one is negative. When we provide direct current to capacitor the positive charge stores on a positive electrode (plate) of a capacitor and negative charge stores on a negative electrode of a capacitor For each particle of positive charge which reaches at a positive electrode a charge of a similar sign will leave from the negative electrode. Due to this, the electrodes endure neutral charging and a potential change due to this charging is recognized amid the two electrodes of capacitors. when the capacitor has its stable state current is incapable to move over the capacitor and about the circuitry due to the dielectric possessions of the dielectric material used to detached the electrode. The motion of electrons over the electrode of the capacitor is recognized as the Charging Current of a capacitor, which flows till that point when applied voltage and voltage across the electrode of the capacitor become equal. This condition is said to be a fully charged condition of a capacitor.

Types of Capacitors

  • Non-polarized Capacitor
  • Polarized Capacitor
  • Variable Capacitor
  • Trimmer Capacitor

Non-polarized Capacitor

This type of capacitor that can be connected any way in a circuit. There is no positive or negative. Common types of non-polar capacitors are ceramic, mica and some electrolytic. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

Polarized Capacitor

A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is used with a resistor in a timing circuit. It can also be used as a filter, to block DC signals but pass AC signals.

Variable Capacitor

A capacitor whose capacitance can be varied. These are usually made up of one or more moving plates and one or more non moving plates separated by the dielectric. By moving the plates, we can vary the capacitance. And it is used in a radio tuner. 

Trimmer Capacitor

This type of variable capacitor is operated with a small screwdriver or similar tool. It is designed to be set when the circuit is made and then left without further adjustment.

How Energy Stored in Capacitor

The quantity of potential existing at the capacitor depending on how much amount of charge was stored on the electrodes by the work done by the power supply and it also depends on the capacitance of capacitor. The given diagram explains this phenomenon. In the diagram, we can see parallel plate capacitor configuration. This capacitor is the basic type of capacitor. It can be made by two metallic electrodes by putting them at a specific distance, and its capacitance can be measured by area of plate and space between them. By changing the distance between capacitors and the area of plate we can change the capacitance of a capacitor which measured in farad. As the capacitor stores power or energy of moving electrons in shape of charge on electrodes, so we can say if the area of plate is larger and distance between them is smaller then capacitor stores more charge on plates. Which means it has larger capacitance. By providing supply to a capacitor and calculating the quantity of charge on plates we can calculate value of capacitance by given formula.

Q/v=C

it can also be written as 

Q= C x V

As we have studied that the charge is a deposit on the electrodes of a capacitor, we can also say that the energy of the charges is deposited in the shape of the electrical field among the two electrodes. When current continues to moves through capacitor it getting charging, so the electrical field also becomes stronger as it supplies more energy among the electrodes. Similar to this if current moving out of capacitor, it starts discharging, and optional alteration amid electrodes getting starts eliminating due to this field stored between plates also decreases.

What is the Capacitance of Capacitor

The ability of a capacitor to deposit charge on its electrodes in the shape of an electrical field is known as Capacitance of Capacitor

We can also say it that it is a feature of a capacitor which stops the alteration of voltage about it. It also is known as the electrical feature of a capacitor and is the capability to storing charge among its two electrodes, which has a unit of Farad (F). We can also define Capacitance as that if one columb of charge is a deposit on electrodes of a capacitor in presence on one volt at its terminal then it has one-farad capacitance.

The point which is noticeable is that C has positive values and not negative. FARAD is a very large unit of calculation, so we use its subs units like uF, nF, pF.

Voltage Rating of a Capacitor

Every capacitor has specific voltage ratings during the selection of capacitor these parameters are the first considered, either how much voltage we can apply across it.

The extreme amount of voltage that can be applied across a capacitor is mentioned in the datasheet of a capacitor, so you should always read to apply a voltage across a capacitor.

If the applied voltage is greater then the specified limit the dielectric material will break down and a short circuit will cause damage capacitor. The operating voltage of the capacitor depends on the dielectric material used and its diameter. A capacitor that is needed to work at a hundred V (AC) must have an OPERATING voltage near two hundred V. In normal conditions, you should select a capacitor that has fifty percent larger voltage capacity than its effective voltage which to be applied. Another main aspect that disturbs the working of a capacitor is for electric leakage current.

This leakage happens in the capacitor due to undesired flow of current through the insulating material. Usually, it is expected that the resistance of the insulating material is enormously higher and a decent dielectric stops the movement of direct current from one plate to another. But, if the insulating substantial gets injured due to extreme voltage or higher temperature, the leak current through the insulator will become very higher subsequent in fast damage of charge on the electrodes and hotness of the capacitor finally subsequent in early damage of the capacitor. So always try to use the capacitor under its specified voltage otherwise it will cause serious damage and can be harmful to your expensive device in which you are using it.

Advantages

  • Long life, with little degradation over hundreds of thousands of cycles.
  • Low cost per cycle
  • Good reversibility
  • Very high rates of charge and discharge.
  • Extremely low internal resistance (ESR) and consequent high cycle efficiency (95% or more) and extremely low heating levels.
  • High output power.

Disadvantages

  • The amount of energy stored per unit weight is considerably lower than that of an electrochemical battery.
  • As with any capacitor, the voltage varies with the energy stored.
  • Has the highest dielectric absorption of any type of capacitor.
  • Cells have low voltages – serial connections are needed to obtain higher voltages.
  • Voltage balancing is required if more than three capacitors are connected in series.
  • Linear discharge voltage prevents use of the full energy spectrum.

Applications

  • They are used in filter applications, energy storage systems, motor starters and signal processing devices.
  • Capacitors are used for power factor correction.
  • Use of capacitors includes smoothing the ripples from AC in power supply, coupling and decoupling the signals, as buffers etc.
  • It can be used in many instruments and circuitries to block direct current and allows other signals to pass on.
  • It can also be used to regulate the frequency retort of an acoustic circuitry or to combine different discrete amplifier circuits that should be endangered from the communication of direct current.


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