Pikofarad

[Baba Flores]

Capacitanceis a physical quantity that represents the ability of a conductor to accumulate charge. It is found by dividing the electrical charge magnitude by the potential difference between conductors:

One farad represents extremely large capacitance for an isolated conductor. For example, an isolated metal ball with the radius 13 times greater than that of the Sun would have a capacitance of one farad, while the capacitance of a metal ball with the radius of the Earth would be about 710 microfarads (μF).

Because one farad is such a large quantity, smaller units are used, such as microfarad (μF), which equals one-millionth of a farad, nanofarad (nF), equalling to one billionth of a farad, and picofarad (pF), which is one-trillionth of a farad.

As time went by, capacitors have been improved, with their size decreasing as the capacitance increased. Today capacitors are widely used in electronics. For example, a capacitor and an inductance coil create a resistor, inductor, and capacitor circuit, also known as an RLC or an LCR or a CRL circuit. This circuit is used to set receiving frequency on a radio.

The second most important property of a capacitor is its rated voltage. Exceeding this value may render the capacitor unusable. This is why when building circuits it is common to use capacitors with the value for the rated voltage that is double compared to the voltage applied to them in the circuit. This way even if the voltage in the circuit slightly increases above the norm, the capacitor should be fine, as long as the increase does not become double the norm.

Capacitors can be joined together to create batteries to increase the total rated voltage or capacitance of the system. Connecting two capacitors of the same type in series doubles the rated voltage and decreases the total capacitance in half. Connecting the capacitors in parallel results in doubling the total capacitance, while the rated voltage stays the same.

Depending on their intended use capacitors are classified into general-purpose capacitors, which do not have to meet high-level requirements, and special capacitors. The latter group includes high voltage capacitors, precision capacitors, and those with different temperature coefficients of capacitance.

Similar to resistors, capacitors are marked according to their capacitance and other properties. The marking could include information on nominal capacitance, the degree of deviation from the nominal value, and rated voltage. Small scale capacitors are marked with three or four digits or alpha-numeric code, and they can also be color-coded.

Tables with codes and their corresponding rated voltage, nominal capacitance, and temperature coefficient of capacitance are available online, but the most reliable way to verify the capacitance and to find out if the capacitor is operating properly is to remove the capacitor from the circuit and to take measurements by using a multimeter.

A word of caution: capacitors can store a very large charge at a very high voltage. To avoid an electric shock it is paramount to take precautions before taking measurements. In particular, it is important to discharge capacitors by short-circuiting their leads with a wire that is insulated with a highly resistant material. Regular wires of a measuring device would work well in this situation.

Polymer capacitors: these types of capacitors use a semiconductor or an organic polymer that conducts electricity instead of electrolytic fluid as the second plate. Their anode is usually made of metal such as aluminum or tantalum.

Supercapacitors are becoming popular these days. A supercapacitor is a hybrid of a capacitor and a chemical power supply source. The charge is stored at the border where the two media, the electrode, and the electrolyte meet. The first electrical component that was the predecessor of a supercapacitor was patented in 1957. It was a capacitor with a double electric layer and a porous material used, which helped increase the capacity because of the increased surface area. This approach is known now as double-layer capacitance. The electrodes were coal-based and porous. Since then the design has been constantly improved, and the first supercapacitors appeared on the market in the early 1980s.

Supercapacitors are used in electric circuits as a source of electric energy. They have many advantages over traditional batteries, including their longevity, small weight, and fast charging. It is likely that due to these advantages supercapacitors will replace batteries in the future. The main drawback of using supercapacitors is that they produce a smaller amount of specific energy (energy per unit of weight) and that they have low rated voltage and large self-discharge.

In Formula 1 races supercapacitors are used in energy recuperation systems. The energy is generated when the vehicle slows down. It is stored in the flywheel, the battery, or the supercapacitors for further use.

In consumer electronics supercapacitors are used to ensure stable electric current or as a backup power supply. They often provide power during the peaks for power demand in devices that use battery power and have variable electrical demand, such as MP3 players, flashlights, automated utility meters, and other devices.

Supercapacitors are also used in public transit vehicles, especially in trolleybuses, because they allow for higher maneuvering ability and self-contained motion when there are problems with the external power supply. Supercapacitors are also used in some buses and electric cars.

In modern devices, the use of touchscreens that control devices through touching panels or screens is on the increase. There are different types of touchscreens, including capacitive and resistive screens, as well as many others. Some can only react to one touch, while others react to multiple touches. The working principles of the capacitive screens are based on the fact that a large body conducts electricity. This large body in our case is the human body.

A surface capacitive touch screen is made of a glass panel, coated with a transparent resistive material. Generally, this material is highly transparent and has low surface resistance. Often the alloy of indium oxide and tin oxide is used. The electrodes in the corners of the screen apply low fluctuating voltage on the resistive material. When a finger touches this screen, it creates a small leakage of the electrical charge. This leakage is detected in the four corners by the sensors and the information is sent to the controller, which determines the coordinates of the touch.

The advantage of these screens is in their longevity. They can withstand touch as frequently as once per second for up to 6.5 years. This translates to about 200 million touches. These screens have a high, up to 90%, transparency rate. Because of their advantages, capacitive touchscreens have been replacing resistive touchscreens on the market since 2009.

The disadvantages of capacitive screens are that they do not work well in sub-zero temperatures and that it is difficult to use them while wearing gloves because gloves act as an insulator. The touchscreen is sensitive to exposure to the elements, therefore if it is located on the external panel of the device, it is only used in the devices that protect the screen from exposure.

Besides surface capacitive screens, there are also projected capacitive touchscreens. They differ in that there is a net of electrodes on the inside of the screen. When the user touches the electrode, the body and the electrode work together as a capacitor. Thanks to the net of electrodes it is easy to get the coordinates for the area of the screen that was touched. This type of screen reacts to touch even if the user is wearing thin gloves.

Projected capacitive touchscreens also have high transparency, up to 90%. They are durable and long-lasting, and this makes them popular not only in personal electronic devices, but also in devices meant for public use, such as vending machines, electronic payment systems, and others.

Pojemność elektryczna oznacza zdolność ciała do przechowywania ładunku elektrycznego. Typowym elementem służącym do magazynowania energii jest kondensator płaski. W kondensatorze płaskim pojemność jest wprost proporcjonalna do pola powierzchni płytek przewodnikw i odwrotnie proporcjonalna do odległości dzielącej te płytki. Pojemność kondensatora płaskiego definiowana jest jako ładunek w zależności od rżnicy potencjałw pomiędzy płytkami.

W elektronice pasywne elementy dwubiegunowe, służące do magazynowania energii, nazywane są kondensatorami. Pojemność tych elementw może wynosić od pojedynczych pikofaradw do dziesiątek faradw. Z tej przyczyny powszechnie stosowane są ułamki dziesiętne farada, a dziesiętnych wielokrotności tej jednostki nie spotyka się prawie nigdy. Do mierzenia pojemności mogą być stosowane multimetry.

W układzie SI jednostką pojemności jest farad. Kondensator o pojemności 1 farada obdarzony ładunkiem elektrycznym 1 kulomba ma pomiędzy płytkami rżnicę potencjałw wynoszącą 1 wolt. Jeden farad jest bardzo dużą jednostką pojemności. Dla porwnania, pojemność kuli ziemskiej wynosi około 700 mikrofaradw. Zarazem nowoczesne kondensatory elektryczne dwuwarstwowe mogą mieć pojemności rządu kilu faradw przy napięciu roboczym wynoszącym do 10 woltw.

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