A capacitor in an AC or DC circuit, which is often called simply a conductor, consists of a pair of plates covered with a layer of insulation. If current is applied to this device, it will receive a charge and keep it in itself for some time. Its capacity largely depends on the gap between the plates.
Content
- Principle of operation
- DC Capacitor Description
- Features of the device with alternating current
Principle of operation
The capacitor can be made in different ways, but the essence of the work and its main elements remain unchanged in any case. To understand how it works, you need to consider its simplest model.
The simplest device has two plates: one of them is positively charged, the other - on the contrary, negatively. Although these charges are opposite, they are equal. They are attracted with a certain force, which depends on the distance. The closer the plates are to each other, the greater the force of attraction between them. Thanks to this attraction, the charged device is not discharged.
However, it is enough to lay any conductor between the two plates and the device will be instantly discharged. All electrons from the negatively charged plate will immediately go to the positively charged one, as a result of which the charge will equalize. In other words, in order to remove the charge from the capacitor, it is only necessary to close two of its plates.
DC Capacitor Description
Electrical circuits are of two types - permanent or variables. It all depends on how the electric current flows in them. The devices on these circuits behave differently.
To consider how a capacitor will behave in a DC circuit, you need:
- Take a constant voltage power supply unit and determine the voltage value. For example, "12 Volts".
- Install a light bulb rated for the same voltage.
- Install a capacitor in the network.
There will be no effect: the light will not light up, and if you remove the capacitor from the circuit, then the light will appear. If the device is connected to the AC network, then it simply will not close, therefore, no electric current will be able to pass here. Permanent - not able to pass through the network in which the capacitor is included. It is all the fault of the plates of this device, or rather, the dielectric that separates these plates.
You can also make sure that there is no voltage in the DC network in other ways. You can connect anything to the network, the main thing is that a source of constant electric current is included in the circuit. An element that will signal the absence of voltage in the network or, conversely, its presence, can also be any electrical device. It is best to use a light bulb for these purposes: it will glow if there is an electric current, and will not light if there is no voltage in the network.
It can be concluded that the capacitor is not capable of conducting direct current through itself, but this conclusion is incorrect. In fact, the electric current appears immediately after the voltage is applied, but instantly disappears. In this case, it passes within only a few fractions of a second. The exact duration depends on how large the device is, but this is usually not taken into account.
Features of the device with alternating current
To determine whether an alternating electric current will pass, it is necessary to connect the device to the appropriate circuit. In this case, the main source of electricity should be a device that generates exactly an alternating electric current.
A constant electric current does not go through a capacitor, but an alternating one, on the contrary, flows, and the device constantly resists the electric current passing through it. The magnitude of this resistance is related to frequency. The relationship here is inversely proportional: the lower the frequency, the higher the resistance. If to source of alternating electric current connect the conder, then the highest voltage value here will depend on the current strength.
To make sure that the capacitor can conduct an alternating electric current, the simplest circuit, made up of:
- Current source. It must be variable.
- Condenser.
- Consumer of electric current. It is best to use a lamp.
However, it is worth remembering one thing: the lamp will light up only if the device has a fairly large capacity. The alternating current has such an effect on the capacitor that the device begins to charge and discharge. And the current that flows through the network during recharging raises the temperature of the lamp filament. As a result, it glows.
The recharging current largely depends on the capacity of the device connected to the AC network. The dependence is directly proportional: the more capacity it has, the greater the value characterizing the recharge current strength. To be convinced of this, it is enough just to increase the capacity. Immediately after this, the lamp will begin to glow brighter, since its filaments will be more heated. As you can see, the capacitor, which acts as one of the elements of the AC circuit, behaves differently than a constant resistor.
When an AC capacitor is connected, more complex processes begin to occur. A tool such as a vector will help you better understand them. The main idea of the vector in this case will be that it is possible to represent the value of a time-varying signal as the product of a complex signal, which is a function of an axis representing time and a complex number, which, on the contrary, is not related with time.
Since vectors are represented by some magnitude and some angle, they can be drawn in the form of an arrow that rotates in the coordinate plane. The voltage on the device lags slightly behind the current, and both vectors, by which they are designated, rotate on a plane against the hour hands.
A capacitor in an AC network can be periodically recharged: it either acquires some kind of charge, or, on the contrary, gives it up. This means that the conductor and the source of alternating electric current in the network are constantly exchanging electrical energy with each other. This type of electricity in electrical engineering is called reactive.
The capacitor does not allow a constant electric current to pass through the network. In this case, it will have a resistance equal to infinity. An alternating electric current is able to pass through this device. In this case, the resistance has a finite value.
