Showing posts with label Capacitor. Show all posts
Showing posts with label Capacitor. Show all posts

Wednesday, February 27, 2019

February 27, 2019

All about Capacitors

Capacitor

A capacitor was formerly known as condenser. It is a device for storing electric charge. Practical capacitors are made using various methods. But in all of them there are at least two conductors separated by an insulation.

 

A pair of conductors separated by a dielectric or insulator forms a capacitor. If we apply a potential difference or voltage across these two conductors, then a static electric field is formed across the insulator or dielectric. Hence, positive charges are stored in a plate or conductor and negative charges in the other. The unit of capacitance is Farad. It is the ratio of electric charge to the potential difference on each conductor.
 



Capacitors are widely used in electronic circuits. It is used to block direct current while allowing alternating current to pass. It is also used in filter networks, for smoothing the output of power supplies. It is also used in the resonant circuits.

To increase the capacitance of a capacitor we have to do two things:
01. Increase the area of the conductors by any means and
02. Narrow the separation between them as much as possible.


Operation of Capacitor:

Capacitors are the general model for electric fields. An ideal capacitor is the one which has a constant capacitance C. Capacitance C, can be defined as the ratio of charge on each conductor to the voltage between them.

C = Q/V

where C is capacitance, Q is charge and V stands for voltage.

In fact, charge build up is a continuous process. And sometimes discharge happens. Or a leakage current may flow. Hence we represent capacitance as the derivative of small charge, q with respect to small voltage v. 

C = dq/dv.

Energy storage

To 'move' charges between the conductors of a capacitor, work must be done. This work is done by a voltage source. When this external influence is removed the capacitor starts discharging and comes to its equilibrium position. The amount of energy stored in a capacitor is the work done in establishing the electric field. It can be expressed as:

 


Networks


Capacitors in parallel:

When we connect capacitors in parallel connection then all the capacitors get same applied voltage. Hence their capacitances add up. Actually the plate area of the capacitors are added up in parallel connection.



Capacitors in series:


But in series connection the plates are much more separated. From the diagram above it is very clear that the separation distance is added up. So the total voltage difference is calculated as sum of the inverse of their capacitance. Hence the total series capacitance must be smaller than any other capacitor in the network.




High working voltage is achieved by combining capacitors in series. For example, a high voltage power supply can produce voltage spikes. Series capacitors are used for smoothing the spikes of a high voltage power supply.

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Tuesday, January 19, 2016

January 19, 2016

Introduction to Capacitors, Capacitance and Charge


The ability to store energy in the form of electric charge is called capacitance. A device designed to possess capacitance is called a capacitor. A capacitor is a two terminal device used to store energy in the form of electric field. The symbol used to represent capacitance is C. A  capacitor in its simplest form a capacitor is nothing more than two conducting plates separated by a sheet of insulator. In capacitors the conductors are called plates and the insulator is called a dielectric. The larger the surface area of the "plates" (conductors) and the narrower the gap between them, the greater the capacitance is.

Basic Capacitor Action

A capacitor stores energy when an electric charge is forced onto its plates by some other energy source, such as a battery. When there is a potential difference across the terminals, i.e. when the capacitor is connected across a battery as shown in figure below, 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. These charges on the plates of the capacitor represent a voltage source just as the charges on the plates of a cell do. Note that in the process of charging the capacitor, no electrons move from one plate to the other plate through the dielectric.
Because of opposing voltages, the current stops once the capacitor is charged. The opposite charges on the plates of the capacitor create a new energy source. The energy stored in the capacitor produces a voltage equal to that of the battery. Since the capacitors voltage is equal to, and in opposition to, the battery voltage , a state of equilibrium exists. No current can flow in either direction.

A charged capacitor can be disconnected from the original energy- source (the battery and used as a new energy source. If a voltmeter is connected to the capacitor, it will register a voltage., if a resistor is connected to the capacitor as shown in figure current will flow through the resistor. However, a capacitor has limited use as a primary energy source for two reasons:
  1. For its weight and size, the amount of energy it can store is small compared with what a battery can store.
  2. The voltage available from the capacitor rapidly diminishes as energy is removed from the capacitor
Although the amount of energy stored in a capacitor is small, capacitor can deliver a shock. The shock can be very severe (even fatal) if the capacitor is large and charged to a high voltage.

Capacitance

Capacitance of a capacitor is defined as the ratio of charge Q on each conductor to the voltage V between them.
                        C = Q / V

Unit of Capacitance

The base unit of capacitance is the Farad. The abbreviation for farad is F. One farad is that amount of capacitance which stores 1 C of charge when the capacitor is charged to 1 V . In other words, a farad is a coulomb per volt  (C / V).

Example:
Question: What is the capacitance of a capacitor that requires 0.5 C to charge it to 25 V?

Given :           Charge (Q) = 0.5 C
                        Voltage (V) = 25 V
Solution :       C = Q/V = 0.5/25 = 0.02

Answer :        The capacitance is 0.02 F.

The 0.02 F calculated above is a very high value of capacitance. In most circuits the capacitance used is much lower. In fact, they are usually so much lower that the base unit of farad is too high to conveniently express their value. The micro-farad (10-6) and the picofarad (pF)(10-12) are more convenient units. Both are used extensively in specifying values of capacitors in electronic circuits. Often it is necessary to convert from one unit to another.
            1000 pF = 1000 x 10-6 mF = 0.001 mF
0.001 mF = 0.001 x 106 pF     = 1000 pF

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Wednesday, August 3, 2011

August 03, 2011

What is a Circuit?

What is a Circuit?


Answer: Simply, circuit is the interconnection of electrical components. 

 
Here in the figure 3 electrical components are connected together with wires. Hence it makes an electrical circuit.

Electrical Components: There are 3 basic electrical components. These are: Resistor, Capacitor and Inductor.


Resistors: These are very simple element except they have a colour coding on their body to mention how much resistance they have. The work of a resistor is very simple, �TO RESIST�. And of course it resists current (electricity).  

This is the symbol of resistors. To know details about resistors click here.



Capacitors:  A capacitor was formerly known as condenser. It is a device for storing electric charge. Practical capacitors are made using various methods. But in all of them there are at least two conductors separated by an insulation.
This is the symbol of capacitors. The symbol plus and minus shows the polarity of the two plates. To know more about capacitors click here. 




The pic above is a conventional capacitor. Present days capacitors look like below:






Inductros: An inductor is also known as reactor or coil. It is a passive electrical component. It can store energy in a magnetic field created by the electric current passing through it. The ability of an inductor to store magnetic energy is called its inductance. The unit of inductance is Henrie. Usually any conductor has inductance. We reinforce the magnetic field of an conductor by giving wound in loops. When we make something where wound of loops of conductors are there and a current flow is available through the two side of the conductor then it becomes and acts like an inductor.



  

 This is the symbol of an inductor. To know more about inductors click here. 




 

The pic above shows some typical inductors. 
 






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