Since the beginning of the study of electricity, it was only in 1745 that Ewald Jurgen von Kleist and Pieter van Muschenbroek managed to solve the problem of its accumulation and preservation. Created in Leiden, Holland, the device made it possible to accumulate electrical energy and use it when necessary.
Leyden jar - a prototype of a capacitor. Its use in physical experiments advanced the study of electricity far ahead, made it possible to create a prototype of electric current.
What is a capacitor
To collect electric charge and electricity is the main purpose of a capacitor. Usually this is a system of two insulated conductors located as close as possible to each other. The space between the conductors is filled with a dielectric. The charge accumulated on the conductors is chosen differently. The property of opposite charges to be attracted contributes to its greater accumulation. The dielectric is assigned a dual role: the greater the dielectric constant, the greater the electrical capacity, the charges cannot overcome the barrier andneutralize.
Electrical capacity is the main physical quantity that characterizes the ability of a capacitor to accumulate charge. The conductors are called plates, the electric field of the capacitor is concentrated between them.
The energy of a charged capacitor, apparently, should depend on its capacity.
Electrical capacity
Energy potential makes it possible to use (large electrical capacity) capacitors. The energy of a charged capacitor is used when it is necessary to apply a short current pulse.
On what quantities does the electric capacity depend? The process of charging a capacitor begins by connecting its plates to the poles of a current source. The charge accumulated on one plate (the value of which is q) is taken as the charge of the capacitor. The electric field concentrated between the plates has a potential difference U.
Electric capacity (C) depends on the amount of electricity concentrated on one conductor and the field voltage: C=q/U.
This value is measured in F (farads).
The capacity of the entire Earth is not comparable to the capacity of a capacitor, the size of which is about the size of a notebook. The accumulated powerful charge can be used in vehicles.
However, there is no way to accumulate an unlimited amount of electricity on the plates. When the voltage rises to the maximum value, a breakdown of the capacitor may occur. platesneutralized, which may damage the device. The energy of a charged capacitor is completely spent on heating it.
Energy value
The heating of the capacitor occurs due to the transformation of the energy of the electric field into internal. The ability of the capacitor to do work to move the charge indicates the presence of a sufficient supply of electricity. To determine how high the energy of a charged capacitor is, consider the process of discharging it. Under the action of an electric field of voltage U, a charge of q flows from one plate to another. By definition, the field work is equal to the product of the potential difference and the amount of charge: A=qU. This ratio is valid only for a constant voltage value, but in the process of discharging on the capacitor plates, it gradually decreases to zero. To avoid inaccuracies, we take its average value U/2.
From the electric capacity formula we have: q=CU.
From here, 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 capacity and voltage. To answer the question of what the energy of a charged capacitor is, let's turn to their varieties.
Types of capacitors
Since the energy of the electric field concentrated inside the capacitor is directly related to its capacitance, and the operation of capacitors depends on their design features, various types of storage devices are used.
- According to the shape of the plates: flat, cylindrical, spherical, etc.e.
- By changing capacitance: constant (capacity does not change), variable (by changing physical properties, we change capacitance), tuning. Changing the capacitance can be carried out by changing the temperature, mechanical or electrical stress. The capacitance of trimmer capacitors varies by changing the area of the plates.
- By dielectric type: gas, liquid, solid dielectric.
- By type of dielectric: glass, paper, mica, metal-paper, ceramic, thin-layer films of various compositions.
Depending on the type, other capacitors are also distinguished. The energy of a charged capacitor depends on the properties of the dielectric. The main quantity is called the dielectric constant. The electrical capacity is directly proportional to it.
Plate 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 and round. If there is a need to obtain a variable capacity, then it is customary to take the plates in the form of half-disks. The 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 to S, the distance between the plates is taken equal to d, the dielectric constant of the filler is ε. The capacitance of such a system depends only on the geometry of the capacitor.
C=εε0S/d.
Energy of a flat capacitor
We see that the capacitance of the capacitor is directly proportional to the total area of one plate and inversely proportional to the distance between them. The coefficient of proportionality is the electrical constant ε0. Increasing the dielectric constant of the dielectric will increase the electrical capacity. Reducing the area of the plates allows you to get tuning capacitors. The energy of the electric field of a charged capacitor depends on its geometric parameters.
Use the calculation formula: W=CU2/2.
Determination of the energy of a charged flat-shaped capacitor is carried out according to the formula:
W=εε0S U2/(2d).
Using Capacitors
The ability of capacitors to smoothly collect an electric charge and give it away quickly enough is used in various fields of technology.
Connection with inductors allows you to create oscillatory circuits, current filters, feedback circuits.
Photo flashes, stun guns, in which an almost instantaneous discharge occurs, use the ability of a capacitor to create a powerful current pulse. The capacitor is charged from a direct current source. The capacitor itself acts as an element that breaks the circuit. The discharge in the opposite direction occurs through a lamp of low ohmic resistance almost instantly. In a stun gun, this element is the human body.
Capacitor or battery
The ability to keep the accumulated charge for a long time gives a wonderful opportunity to use it as an information storage or energy storage. This property is widely used in radio engineering.
Replace the battery, unfortunately, the capacitor is not able, because it has the peculiarity of being discharged. The accumulated energy does not exceed a few hundred joules. The battery can store a large amount of electricity for a long time and almost without loss.
