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Electrical charge on one plate.

Some of the most commonly used electronic components are condencators. And in this article we have to figure out what they consist of how they work and what

Let's first consider constressor deviceAnd then we smoothly move on to their main types and characteristics, as well as to charging / discharge processes. As you can see, today we have to study many interesting moments 😉

So, the simplest condenser is two flat conductive plates located in parallel to each other and separated by a dielectric layer. Moreover, the distance between the plates should be much smaller than, in fact, the dimensions of the plates:

Such a device is called flat condenserand plates - clipped condenser. It is worth clarifying that here we consider the already charged condenser (the charging process itself is studying a little later), that is, on the plates focused on a certain charge. Moreover, the greatest interest is the case when the charges of the condenser plates are the same by the module and are opposite to the sign (as in the figure).

And since the plates focused on the charge, the electric field depicted by arrows in our scheme arises between them. The field of a flat capacitor is mainly concentrated between the plates, however, in the surrounding space also an electric field occurs, which is called the scattering field. Very often, its influence in the tasks neglected, but it's not worth forget about him 🙂

To determine the magnitude of this field, consider another schematic image of a flat capacitor:

Each of the capacitor plates separately creates an electric field:

The expression for the field strength of a uniformly charged plate is as follows:

Here is the superficial charge density :. A - dielectric permeability of a dielectric located between the condenser's plates. Since the area of \u200b\u200bthe condenser plates we have the same, as well as the value of the charge, then the tension modules electric fieldare equal to each other:

But the directions of the vectors are different - inside the vector condenser are directed in one direction, and outside - to the opposite. Thus, inside the plates the resulting field is determined as follows:

And what will be the magnitude of tension outside the condenser? And everything is simple - on the left and right of the fields of the field plates compensate each other and the resulting tension is 0 🙂

Charging processes and discharge capacitors.

We dealt with the device, we will now understand what will happen if the DC source is connected to the condensector. On principled electrical circuits The condenser is indicated as follows:

So, we have connected the capacitor plates to the Poles of the DC source. What will happen?

Free electrons from the first plating condenser Right to the positive pool of the source, in connection with which the lack of negatively charged particles will arise on the plated and it will become positively charged. At the same time, the electrons from the negative pole of the current source will move to the second condenser cover, as a result of which the excess electrons will arise on it, respectively, the Oblast will become negatively charged. Thus, on the plates of the capacitor, charges of different sign are formed (just this case, we considered in the first part of the article), which leads to the appearance of an electric field, which will create between the capacitor plates defined. The charging process will continue until this potential difference becomes equal to the voltage of the current source, after that the charging process will end, and the movement of electrons by chain will stop.

When the source is disconnected, the capacitor can save accumulated charges for a long time. Accordingly, the charged condenser is a source of electrical energy, which means that it can give energy to the outer chain. Let's create the simplest chain, simply by connecting the condenser's plates with each other:

In this case, the chain will begin to flow condenser discharge currentAnd electrons will begin to move with a negatively charged attachment to positive. As a result, the voltage on the condenser (the potential difference between the plates) will begin to decrease. This process will end at the moment when the charges of the capacitors plates become equal to each other, respectively, the electric field between the plates will disappear and the current will stop the circuit. This is how the discharge of the capacitor occurs, as a result of which he gives to the outer chain all the accumulated energy.

As you can see, there is nothing complicated here.

Capacity and energy of the condenser.

The most important characteristic is the electrical capacitance of the condenser - the physical value, which is defined as the ratio of the charge of the capacitor of one of the conductors to the potential difference between the conductors:

The container varies in the pharands, but the value of 1 f is quite large, so the capacitors are most often measured in micropraids (ICF), nanoforades (NF) and picofarades (PF).

And since we have already brought the formula to calculate tension, let's express the voltage on the condenser as follows:

Here we have the distance between the plates of the condenser, and the charge of the condenser. We substitute this formula in the expression for the capacitance of the capacitor:

If the air appears as a dielectric, then in all formulas you can substitute

For the stored energy of the capacitor, the following expressions are valid:

In addition to the capacitance, the capacitors are characterized by another parameter, namely the magnitude of the voltage, which can withstand its dielectric. With too large voltage values, the dielectric electrons are separated from atoms, and the dielectric begins to carry out the current. This phenomenon is called a capacitor's breakdown, and as a result of the plated turns out to be closed with each other. Actually, the characteristic that is often used when working with capacitors is not a breakdown voltage, but the operating voltage is that there is a voltage value in which the capacitor can work indefinitely for a long time, and the breakdown will not happen.

In general, we reviewed today the basic properties of capacitors, their device and characteristics, so that in this end the article, and in the next we will discuss various options for condensers, so come to our site again!

As you know, there is an electric field around the charged bodies that has energy.

Is it possible to accumulate charges and electric field energy? A device that allows you to accumulate charges is capacitor (from lat. Condensare - condensation). The simplest flat condenser consists of two identical metal plates - plates located on a short distance From each other and separated by a layer of dielectric, for example, air (Fig. 83). The thickness of the dielectric in comparison with the size of the plates is small.

Fig. 83. The simplest condenser and its designation in the scheme

We will demonstrate the ability of the capacitor's ability to accumulate charges. For this, two metal plates connect to different poles of the electrophore machine (Fig. 84). Plates will receive the same module, but different by the sign of charges. There will be an electric field. The electrical field of the capacitor is practically focused between the plates inside the condenser.

Fig. 84. Charging the capacitor from the electro-form

After turning off the electrophore charges of charges on the plates and the electric field between them will be saved.

If the stacking of the charged condenser is to connect the conductor, then the conductor will pass the current for some time. So, the charged condenser is a source of current.

Depending on the dielectric, condensers are several types: with solid, liquid and gaseous dielectric. They are distinguished in the form of the folds: flat, cylindrical, spherical, etc. (Fig. 85).

Fig. 85. different types condensers

The properties of the condenser accumulate electrical charges is characterized electricity, or tank. In order to understand what this physical value depends, we turn to the experience.

Two metal plates, reinforced on insulating supports parallel to each other, connect with an electrometer. One of the plates is connected to the electrometer with a rod, another ground, connecting with the instrument housing (Fig. 86, a). The electrical ball is touched by the outer side of the plate A, thereby informing her positive charge + q. Under the action of the electric field, the plate and in the plate in the reallocation of charges: negative charges will be located on the inside of the plate. Free electrons will come from the ground to neutralize the positive charges on the outside of the plates of V. Thus, on the plate in the value equal to the negative charge -Q.

Fig. 86. The dependence of the capacitor capacity from the area, the distance between the plates, the dielectric between the plates

The electrometer arrow will deviate from the zero position. With the help of the same charged balls, we continue to transfer the charges condenser consistently equal to portions. We note that with increasing charge in 2, 3, 4 times, respectively, 2, 3, 4 times the indications of the electrometer will increase, i.e. the voltage between the capacitor plates will increase. Moreover, the ratio of the charge will remain permanent to the voltage:

The value measured by the charge ratio of one of the plates of the capacitor to the voltage between the plates is called the power capacity of the capacitor.

The power consumption of the capacitor is calculated by the formula:

The unit (f) is accepted per unit of capacity in SI, the name is given in honor of the English physics of Michael Faraday. The power consumption of the capacitor is equal to one if the charge of 1 CL is the voltage 1B occurs.

1 f is a very large capacity, so in practice the microfarad (ICF) and picophaderad (PF) are used.

1 μF \u003d 10 -6 f; 1 PF \u003d 10 -12 F.

Throw out what the capacitance of the Condestator depends on. To do this, take a capacitor with plates having a large area (Fig. 86, b). We repeat the experience. The ratio of charge to voltage and in this case remains permanent

but the ratio of charge to tension is now greater than in the first experience, i.e. C1\u003e S. The greater the area of \u200b\u200bthe plates, the greater the capacitor capacity.

Once again I will do the first experience, but now we will change the distance between the plates (Fig. 86, c). With a decrease in distance between the plates, the voltage between them is reduced. With a decrease in the distance between the capacitor plates with the unchanged charge of the capacitor capacity increases.

We will do another experience. We install the plates of the condenser A and at some distance from each other. Plate and charge. Note the testimony of the electroometer when the air is located between the plates. Place a sheet from plexiglas or another dielectric (Fig. 86, g) between the plates. We note that the voltage between the plates will decrease. Consequently, the capacitance of the capacitor depends on the properties of the submitted dielectric.

When making a dielectric capacitance of the capacitor increases.

Condenser, like any charged body, has energy. Check it on experience. Charge a capacitor and connect a light bulb to it. Light bulb flames brightly. This suggests that the charged condenser has energy. The condenser energy turns into the internal energy of the filament of the lamp and wires. In order to charge the condenser, it was necessary to work on the separation of positive and negative charges. In accordance with the law of conservation of energy, perfect work A is equal to the energy of the condenser E, i.e.

where e is the energy of the condenser.

The work that the electrical field of the capacitor makes, can be found by the formula:

where USR is the average voltage value.

Since in the process of discharge, the voltage does not remain constant, it is necessary to find the average voltage value:

USR \u003d u / 2; Then a \u003d qu cp \u003d QU / 2,
since Q \u003d Cu, then a \u003d Cu 2/2.

So, the power of the capacitor with the C capacitance will be equal to:

Capacitors can accumulate energy for a long time, and when they discharge, they give it almost instantly. The properties of the condenser accumulate and quickly give electrical energy is widely used in electrical and electronic devices, in medical equipment (X-ray machinery, electrotherapy devices), in the manufacture of dosimeters, aerial photography.

Questions

What are the capacitors for?
What characterizes the electrostilence of the capacitor?
What is taken per unit of electricity in si?
What depends on the power of the capacitor?

Exercise 38.

Plates of a flat capacitor are connected to a voltage source in 220 V. The capacitance of the capacitor is 1.5 10 -4 μF. What will be the charge of the condenser?
The charge of the plane capacitor is 2.7 10 -2 CL, its capacity is 0.01 μF. Find the voltage between the capacitor plates.

The task

Using the Internet, find how the first condenser was arranged - Leiden Bank. Make it.
Prepare a speech about the history of the condenser.

1. 250V. 2. 55V. 3. 10V. 4. 45V.

Question2.

What is the category arising in a gas tube at low pressures?

1. Arc. 2. Small. 3. Sparkov. 4. Crown. 5. Plasma.

Question3.

What is the name of the electron emitting process with a heated metal cathode?

1. Electrolysis. 2. Electrolytic dissociation.

3. Thermoelectronic emission. 4. Impact ionization.

Question 4.

What is equal to EMF induction in a conductor with a length of 2 m moving in a magnetic field with

B \u003d 10 TL at a speed of 5 m / s along magnetic induction lines.

1. 0B. 2. 10 V. 3. 50 V. 4. 100 V.

Question 6.

To determine the inductance of the coil, if the electric current is passed on it by force 5 A, the magnetic flow of 100 WB arises near the coil.

1. 4 GG. 2. 5 Gn. 3. 20 GG. 4. 100 Gn.

Question 7.

What is energy equal to magnetic field Coils with l \u003d 200 mp at the strength of current in it equal to 5a?

1. 0.025 J. 2. 0.25 J. 3.5 J. 4. 25 J.

Question 9.

When the frame rotates in the magnetic field at its ends, an EDC occurs, changing over time by law: e \u003d 10 sin 8 t. What is the maximum value of the EDF, if all the values \u200b\u200bin the equation are given in the SI system?

1. 4 V. 2. 5 V. 3. 8 V. 4. 10 V.

Question 10.

The active value of the voltage on the plot of chain alternating current Is 100 V. What is approximately equal to the amplitude voltage value in this area?

1. 100 V. 2. Approximately 142 V. 3. 200 V. 4. Approximately 284 V.

Question 11.

The oscillating circuit is connected to: AC source. With what condition arises resonance in this oscillatory circuit?

1. If the frequency of the AC source is less than the frequency of own

2. If the frequency of the AC source is equal to the frequency of own oscillations

oscillatory circuit.

3. If the frequency of the AC source is greater than the frequency of own

oscillations of the oscillating circuit.

Question 12.

What physical phenomenon is based on the principle of the transformer?

1. On the creation of a magnetic field moving electric charges.

2. On the creation of an electric field moving electrical charges.

3. On the phenomenon of electromagnetic induction.

Question 13.

Where will the lines of the intensity of the vortex electric field be directed while increasing the magnetic field?

Question 14.

The transmitting and receiving vibrators Hertz are mutually perpendicular. Are there any oscillations in the receiving vibrator?

1.De, very strong. 2. Yes, but weak. 3. It will not arise.

Question 15.

What device in the receiver A. S. Popova serves as a sensitive indicator of electromagnetic waves?

1. Antenna. 2. Coherer. 3. Electromagnet.

4. Grounding. 5. Coil. 6. Power Battery.

Question 16.

Why do the air gap between the anchor and the inducer of the generator strive to make as smaller as possible?

1. To reduce the size of the generator.

2. To increase the scattering of the magnetic field.

3. To reduce the scattering of the magnetic field.

Question 17.

Which of the listed emissions has the lowest frequency?

1. Ultraviolet rays. 2. Infrared rays.

3. Visible light. 4. Radio waves.

Question 19.

The detector radio receives signals from a radio station operating on the wave

30 m. What is the frequency of oscillations in the oscillatory circuit of the radio?

1.10 ^ -7 Hz. 2.10 ^ 7 Hz. 3. 9 * 10 ^ 9 Hz.

Question 20.

What radio waves give the most reliable radio communication with sufficient power of the transmitting radio station?

1. Long waves. 2. Medium waves. 3. Corn waves. 4. Ultrashort waves.

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