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Measuring the capacity of the capacitor with a nominal capacitance of 10 μF, using a multimeter oscilloscope.Capacitance is 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:C = Q/∆φHere Q is electric charge, which is measured in coulombs (C), and ∆φ is the potential difference, which is measured in volts (V).Capacitance is measured in farads (F) in SI. This unit is named after the British physicist Michael Faraday.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.In the extended CGS for electromagnetic units, the main unit of capacitance is described using centimeters (cm).
One centimeter of electromagnetic capacitance represents capacitance of a ball in a vacuum that has the radius of 1 cm. CGS system stands for centimeter-gram-second system — it uses centimeters, grams, and seconds as the basic units for length, mass, and time. Extensions of CGS also set one or more constants to 1, which allows to simplify certain formulas and calculations. Uses for Capacitance Capacitors — Electronic Components for Storing Electric Charges.
Parallel RLC circuit: a resistor, an inductor, and a capacitor Some HistoryScientists were able to make capacitors as far as 275 years ago. In 1745 in Leyden the German physicist Ewald Georg von Kleist and a physicist from the Netherlands Pieter van Musschenbroek made the first capacitor device that was called a “Leyden jar”.
The walls of the jar served as a dielectric, while the water in the jar and the hand of the experimenter acted as conductor plates. Such a jar could accumulate a charge of about one microcoulomb (µC). Experiments and demonstrations with the Leyden jars were popular at the time. In them, the jar was charged with static electricity by using friction. A participant of the experiment would then touch the jar and experience an electric shock. Once 700 monks in Paris conducted the Leyden experiment.
They held hands and one of them touched the jar. At that moment all 700 people exclaimed in horror as they felt the jolt.The “Leyden jar” came to Russia thanks to the Russian Tsar Peter the Great.
He met with Pieter van Musschenbroek during his travels in Europe and became acquainted with his work. When Peter the Great established the Russian Academy of Sciences, he commissioned Musschenbroek to make various equipment for the Academy.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.There are several types of capacitors that differ in whether their capacitance is constant or variable, and in the type of dielectric material used. Examples of Capacitors. Electrolytic capacitors in the power supply unit.There are many different kinds of capacitors made today for a range of uses, but their main classification is based on their capacitance and rated voltage.Generally, capacitance of capacitors falls between several picofarads to several hundred microfarads.
Supercapacitors are an exception to this because their capacitance is formed differently, compared to other capacitors — it is, in fact, double-layer capacitance. This is similar to the operating principle of electrochemical cells. Supercapacitors, which are built with carbon nanotubes, have an increased capacitance because of a larger surface of the electrodes. The capacitance of supercapacitors is tens of farads, and sometimes they can replace electrochemical cells as a source of electric current.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 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 in order 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 rated voltage stays the same.The third most important property of capacitors is their temperature coefficient of capacitance. It reflects the relationship between capacitance and temperature.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.
Capacitor MarkingsSimilar 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 an 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. Disassembled electrolytic capacitor. It is constructed from two aluminum foils.
One of them is coated with an insulating oxide layer and is acting as the anode. A paper soaked in electrolyte together with another foil is acting as the cathode. The aluminum foil is etched to increase its surface area.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.Electrolytic capacitors: these capacitors have large volumetric efficiency. This means that they have a large capacitance for a given unit of the capacitor’s weight. One of the plates of such a capacitor is usually an aluminum ribbon, covered with a thin layer of aluminum oxide. The electrolytic fluid acts as the second plate. This fluid has electrical polarity, therefore it is paramount to ensure that such a capacitor is added to the circuit correctly, according to its polarity.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. 3-Section air variable capacitorVariable capacitors: the capacitance of these capacitors can be changed mechanically, by adjusting electrical voltage, or by varying temperature.Film capacitors: their capacitance can range from 5 pF to 100 μF.There are also other types of capacitors. SupercapacitorsSupercapacitors 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 a number of 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. Electric car A2B made at the University of Toronto. General viewIn 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.
Electric car A2B made at the University of Toronto. Under the hoodThese days many companies produce electric cars, including General Motors, Nissan, Tesla Motors, and Toronto Electric. A research group at the University of Toronto together with the electric motor distributor company Toronto Electric developed a Canadian model of an electric car, A2B. It uses both chemical sources of energy and supercapacitors — this way of storing energy is called hybrid electric storage. The engines of this electric car are powered by the batteries that weigh 380 kg.
Solar panels are also used for additional charge — they are installed on the car’s roof. Capacitive TouchscreensIn 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. 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. Surface Capacitance Touchscreens. Sensor screen for the iPhone is made using the projected capacitance technology.A surface capacitance 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.
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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. Projected Capacitance TouchscreensBesides surface capacitance screens, there are also projected capacitance 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 capacitance 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, including those outside, such as vending machines, electronic payment systems, and others.Este artigo foi escrito por, Tatiana Kondratieva.