What is a Capacitor?
It is defined as the ratio of the electric charge Q to the potential difference V.
C = Q / V
The capacitance of a capacitor is measured in units called Farads. A capacitor is said to have one Farad of capacitance only if the capacitor can hold one ampere per second of electrons at one volt at a rate of one coulomb of electrons per second.
The Evolution of Capacitors
The evolution of capacitors took place in an interesting way. In the 6th century, a Greek scientist ‘Thales of Mileus’ rubbed amber with animal fur. The amber acquired the ability to pick up small bits of material. After several thousands of years have passed (in the 18th century) many changes took place. Von Kleist built the first practical capacitor. He took a medical bottle and filled it partly with water, and then sealed it well with a cork. Later he pushed a nail through the cork into the water. Next, the nail was made to contact with the electrostatic machine, this produced some charge. When Von Kleist was about to touch the nail, he felt the separated charges were able to reunite by flowing through his own body.
One of the famous experiments was Leyden Jar. Van Musschenbroek conducted an experiment which can be said as the first capacitor. His experiment was almost similar to Von Kleist’s one; however, he just removed water from the bottle and used metallic foil to wrap both inside and outside of the jar. There was a metal chain which was driven through the cork on the top of the jar. This chain was hooked with something that would produce the charge. The moment charge was delivered, the jar would hold two equal but opposite charges in equilibrium until they were connected with a wire slightly producing either spark or shock.
A scientist named Daniel Gralath was the first to combine several jars in parallel to form a battery.
This experiment went on to another step ahead of the conclusion given by a great scientist Benjamin Franklin. He told that the charge was stored in the glass, not in the water. So, this made him to replace with a dielectric sheet like an oiled paper sandwiched in between the sheets of metal foils which were rolled or folded into a small package.
Finally, the experiment took a good shape when Michel Faraday added his contribution. He came up with a concept of dielectric constant. He not only invented the first practical fixed capacitor and variable capacitor, but also first usable capacitor which was made from large oil barrels.
Symbols Of Different Capacitors
Symbols and Practical Diodes in the Real Time Applications:
Capacitors are measured in the units Farad. Most of the values are in micro Farad. Micro farad is one millionth of a Farad. The PicoFarad is one millionth of a Micro Farad. It is used in radio works. The Pico Farad capacitor size is larger than Micro Farad capacitor. Some of the capacitors are unpolarized like resistors. They can be placed in either way in a circuit. Electrolytic Capacitors have anode and cathode that needs to be placed in a particular direction. Electrolytic capacitors evaporate after 2000 hours at 105 degrees Celsius.
Construction of a Capacitor
The basic model of capacitor is made of two plate metals which are separated by a dielectric material. From this basic concept of construction, capacitors have evolved into many different models of construction.
Construction Of Capacitor
Real capacitors are made by taking thin strips of metal foil and dielectric material, and then sandwiching them together.
In an Aluminum Electrolyte Capacitor there is an aluminum foil, an electrolyte and porous paper.
In ceramic capacitors, ceramic acts as a dielectric material.
In the air capacitors, air is used as a dielectric medium. In the future, owing to advanced technology capacitors will be made by using different kinds of dielectric material that make them simple, multipurpose and also economical.
Capacitor’s Working Principle
A capacitor in a given supply, current starts flowing into the capacitor. The charge gets struck on both plates as they are separated by a dielectric medium. The electrons that are negatively charged particles are on one of the plates; this makes the plate negatively charged. These large mass of negative charges repel with the like charges on the other plate making it positively charged.
Now these negative and positive charges get attracted to each other which create an electric field in between the plates as they are being separated by an insulating material. This phenomenon is just like storing energy in a battery.
The positive and negative charges try to approach together to form one whole mass on the capacitor plates, the capacitor becomes charged. A capacitor has the ability to retain its electric field; this is because both positive charge and negative charge attracts each other, but never reach each other. At the saturation point, capacitor plates are fully charged and cannot accept any more charges. This stage is called as the capacitance of the capacitor.
Polarized Capacitor is also called as electrolytic capacitors. It is used in DC applications, higher leakage current, small size capacitors, low frequency response and high capacitance. It acts as a short circuit when connected in the wrong way. These capacitors are mainly applicable in regulating voltage fitting, and smoothing decoupling of power supply.
Non-Polarized Capacitor is used in AC applications. When two identical polarized capacitors connected back to back with one of them in reversed, then they act as a non-polarized capacitor with only half of its capacitance. But this has only low frequency. If one is in need of high frequency, then a non-polarized capacitor has to be used. It is used in loudspeakers.
Different Types Of Capacitors
Electrolytic capacitors are polarized capacitors that have anode and cathode. They use high dielectric constant of the aluminum oxide layer on the plates of the capacitor. This is greater than normal dielectric material.
Construction of Electrolytic Capacitors
The basic capacitor has two plates and one dielectric material. In electrolytic capacitor two plates and foils are slightly different. One of the plates is coated with an oxide layer and the paper is soaked in electrolyte which is placed in between the plates. The foil insulated with oxide layer is the anode. The thickness of the anode oxide is a thin film. The second foil acts as a cathode. This has to be packaged together and form a cylinder. Now, this is placed in an aluminum can to protect it from external force. While manufacturing the electrolytic capacitor, it is necessary to use high purity foil of anode. The general thickness would be 20µm and 50µm.
It is mainly used in military and space applications, and also in devices requiring very low leakage currents or in long life characteristics and also to generate high temperatures up to 125 °C.
Ceramic capacitors are of fixed values, which cannot be varied. In this capacitor, ceramic acts as the dielectric and two electrodes have it at their extreme ends.
Ceramic capacitors are available in three main types
- Surface Mounted Multilayer Ceramic Capacitors
- Lead Disc Ceramic Capacitor
- Specialist Microwave Bare Leadless Disc Ceramic Capacitor
Ceramic capacitors are available in smaller ratings, typically between 1nF and 1µF, although values up to 100µF are possible. These are small in size, and have low rated voltage. It is a non polarized capacitor and can be connected to an AC source.
Construction Of Ceramic Capacitor
Ceramic capacitors are made up of fine ground granules of par electric or ferro electric materials. These are mixed in such a way to get desired characteristics. The manufacture coats them with ceramic disc and uses silver contacts on both sides. To get large capacitance, these devices are made up of multiple layers.
Applications of Multilayer Ceramic Capacitors include Consumer electronics, data processing, hard disks, video cameras, DVDs, mobile phones, general electronic circuits and telecommunications.
Variable capacitors are obtained in both mechanical and electrical way. They are mostly used in L/C circuits to set the resonance circuits. The variable capacitors are used in Radio, Television, etc.
Capacitors are used:
- To block the flow of DC and permits AC
- To couple the sections
- To send desired signals to any sections
- For phase shifting
- For creating delay time
- In grounding the undesired frequencies
- In motor starter
- To filter the ripples in a rectifier circuit and wave forms
Applications Of Capacitor
- Capacitor as a Filter: Capacitor is of low pass filter and high pass filter. The reactance of the capacitor is inversely proportional to the frequency. So, we can decrease or increase any circuit at a certain frequency.
- Capacitor as a Discharge Unit: Capacitor has a property of charging and discharging. This application can be used for triggering, ignition and triggering for high scale in power source.
- Snubber Capacitors: It is used to limit the high voltage transient across the circuits.
Thus, this is all about evolution and different types of capacitors. It is used in smooth power supply, audio frequency coupling, in RF coupling capacitor applications and in tunes circuits.