Since the beginning of the study of electricity to solvethe question of its accumulation and conservation was possible only in 1745 to Ewald Jürgen von Kleist and Peter van Muschenbruck. Created in the Dutch Leiden device allows you to accumulate electrical energy and use it if necessary.
Leyden Bank - a prototype of a capacitor. Its use in physical experiments advanced the study of electricity far in advance, which allowed the creation of a prototype of electric current.
What is a capacitor
Collect electric charge and electricity -the main purpose of the capacitor. This is usually a system of two insulated conductors located as close as possible to each other. The space between the conductors is filled with dielectric. The charge accumulated on the conductors is chosen opposite to each other. The property of opposite charges attracts to its greater accumulation. The dual role is assigned to the dielectric: the greater the dielectric constant, the greater the electrical intensity, the charges cannot overcome the barrier and neutralize.
Electric intensity is the main physical quantity characterizing the ability of a capacitor to accumulate charge. Conductors are called plates; the electric field of a capacitor centers between them.
The energy of a charged capacitor, apparently, should depend on its capacity.
Electric capacity
The energy potential makes it possible to use (large electric capacity) capacitors. The energy of a charged capacitor is used when necessary to apply a short current pulse.
От каких величин зависит электроемкость?The process of charging a capacitor begins with the connection of its plates to the poles of the current source. The charge accumulated on one plate (the value of which q) is taken as the charge of the capacitor. The electric field concentrated between the plates has a potential difference U.
Electric intensity (C) depends on the amount of electricity concentrated on a single conductor and the field voltage: C = q / U.
This value is measured in f (farad).
The capacity of the entire Earth cannot be compared with the capacity of a capacitor, which is approximately the same size as a notebook. Accumulated powerful charge can be used in the technique.
However accumulate unlimitedelectricity on the plates is not possible. If the voltage rises to the maximum value, a capacitor breakdown may occur. Plates are neutralized, which can lead to damage to the device. The energy of a charged capacitor is fully heated.
Amount of energy
The heating of the condenser is due toconversion of electric field energy into internal one. The ability of the capacitor to perform work on the movement of the charge indicates the presence of an adequate supply of electricity. To determine how high the energy of a charged capacitor is, consider the process of its discharge. Under the action of an electric field with a voltage U, a charge of magnitude q flows from one plate to another. By definition, the field operation is equal to the product of the potential difference by the amount of charge: A = qU. This ratio is valid only for a constant value of voltage, but in the process of discharge on the plates of the capacitor there is a gradual decrease to zero. To avoid inaccuracies, take its average U / 2.
From the formula of electric capacity we have: q = CU.
Hence, the energy of a charged capacitor can be determined by the formula:
W = CU2/ 2.
We see that its value is the greater, the higher the electrical intensity and voltage. To answer the question of what is the energy of a charged capacitor, let us turn to their varieties.
Types of capacitors
Since the energy of the electric field,concentrated inside the capacitor, is directly related to its capacity, and the operation of capacitors depends on their design features, using different types of drives.
- The shape of the plates: flat, cylindrical, spherical, etc.
- По изменению емкости:constant (capacity does not change), variables (changing physical properties, changing capacity), trimmers. Changing the capacitance can be done by changing the temperature, mechanical or electrical voltage. Electrical capacity trimming capacitors varies by changing the area of the plates.
- By type of dielectric: gas, liquid, with a solid dielectric.
- By the type of dielectric: glass, paper, mica, metal-paper, ceramic, thin-layer films of different composition.
Depending on the type, there are othercapacitors. The energy of a charged capacitor depends on the properties of the dielectric. The basic quantity is the dielectric constant. Electric intensity is directly proportional to it.
Flat capacitor
Consider the simplest device for collecting electric charge - a flat capacitor. This is a physical system of two parallel plates, between which there is a dielectric layer.
The shape of the plates can be both rectangular andround. If there is a need to obtain a variable capacity, the plate is usually taken in the form of half-disks. Rotation of one plate relative to another leads to a change in the area of the plates.
We assume that the area of one plate is equal toS, the distance between the plates is taken equal to d, the dielectric constant of the filler is ε. The electrical capacity of such a system depends only on the geometry of the capacitor.
C = εε0S / d.
Energy flat capacitor
We see that the capacitor capacitance is directly proportional to the total area of one plate and inversely proportional to the distance between them. The proportionality coefficient is the electric constant ε0. Увеличение диэлектрической проницаемости dielectric will increase electrical intensity. Reducing the area of the plates allows to obtain trimming capacitors. The electric field energy of a charged capacitor depends on its geometrical parameters.
Use the calculation formula: W = CU2/ 2.
Determination of the energy of a charged capacitor of a flat shape is carried out according to the formula:
W = εε0S u2/ (2d).
Use capacitors
The ability of capacitors to smoothly collect electric charge and quickly enough to give it is used in various fields of technology.
The connection with inductors allows you to create oscillatory circuits, current filters, feedback circuits.
Фотовспышки, электрошокеры, в которых происходит almost instantaneous discharge, use the ability of a capacitor to create a powerful current pulse. The capacitor is charged from a constant current source. The capacitor itself acts as an element breaking the circuit. The discharge in the opposite direction occurs through the lamp of small ohmic resistance almost instantly. In the stun gun this element is the human body.
Capacitor or battery
Ability to keep accumulated for a long timeThe charge provides a wonderful opportunity to use it as an information storage or energy store. In radio engineering, this property is widely used.
Replace the battery, unfortunately the capacitor is notable, because it has a feature to discharge. The accumulated energy does not exceed a few hundred joules. The battery can save a large supply of electricity for a long time and almost without loss.
