The energy of a charged capacitor application of capacitors presentation. Open lesson "capacitors"

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Lesson Objectives:

• Learn to determine the energy of a charged capacitor.
• Develop the ability to apply physical laws in solving problems.
• Find out the practical significance of the capacitor.

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Capacitors.

A capacitor consists of two conductors separated by a dielectric layer, the thickness of which is small compared to the dimensions of the conductors.

The capacitance of a flat capacitor is determined by the formula:

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The energy of a charged capacitor.

E - q + q

The energy of a capacitor for the potential energy of a charge in a uniform field is:

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Application of capacitors

Types of capacitors:

Air,

Paper,

Mica,

Electrostatic.

Purpose:

• Accumulate for a short time charge or energy for a rapid change in potential.
• Do not pass direct current.
• In radio engineering - an oscillatory circuit, a rectifier.
• Application in photography.

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Consolidation.

Theoretical material on the questions:

• What are capacitors for?
• How is a capacitor arranged?
• Why is the space between the plates of a capacitor filled with dielectrics?
• What is the energy of a charged capacitor?

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Problem solving:

1. What is the capacity of the capacitor. If he received a charge of 6 . 10-5 C, from a source of 120 V.

The simplest flat capacitor consists of two identical parallel plates (called plates) located at a small distance from each other and separated by a dielectric layer. Charges of the same modulus but opposite in sign are applied to the plates from the power source. Thus, a potential difference arises between the plates. The entire electric field is concentrated inside the capacitor and is uniform.

The main characteristic of a capacitor is the electrical capacity (capacity), which is denoted by the letter C. The electrical capacity is a physical quantity that characterizes the ability of two conductors to accumulate electric charge. The SI unit of electric capacitance is named after the great scientist Michael Faraday and is called the farad. One farad is a very large value, therefore, in practice, microfarads, nF, pF are used.

The capacitance of two conductors is the ratio of the charge of the conductor to the potential difference between them. The electric capacitance does not depend either on the charge imparted to the conductors or on the potential difference between them. The capacitance of a capacitor is determined by the geometric dimensions of the conductors, the shape, location and, of course, the dielectric constant of the medium. The capacitance of two conductors is the ratio of the charge of the conductor to the potential difference between them. The electric capacitance does not depend either on the charge imparted to the conductors or on the potential difference between them. The capacitance of a capacitor is determined by the geometric dimensions of the conductors, the shape, location and, of course, the dielectric constant of the medium.

To charge a capacitor, work must be done to separate the positive and negative charges. According to the law of conservation of energy, this work is equal to the energy of the capacitor. To charge the capacitor, work must be done to separate positive and negative charges. According to the law of conservation of energy, this work is equal to the energy of the capacitor

Scope: 1) radio engineering and electrical engineering 1) radio engineering and electrical engineering 2) in photography, the well-known flash. 2) in photographic technology, the well-known flash. 3) in laser technology. 3) in laser technology. 4) in the elements of computer memory and your favorite computer. After all, there are capacitors under the covers of the numbers and symbols of the computer keyboard. 4) in the elements of computer memory and your favorite computer. After all, there are capacitors under the covers of the numbers and symbols of the computer keyboard. 5) the capacitor has found application in measuring the humidity of air and wood, 5) the capacitor has found application in measuring the humidity of air and wood, 6) in a short circuit protection system. 6) in the short circuit protection system.

Today we have an unusual lesson. We have guests. Let's say hello to them. Please sit down.

Each of you has a lesson card on your desk. Sign your name on it. After completing each task, you will put down the number of points for completing the task in it. At the end of the lesson, we will calculate the total number of points and set the appropriate grade.

Checking the studied material.

Physical dictation.

(after completion - mutual verification).

1 option.

1). A conductor is a substance in which ... (free charges can move throughout the volume).

2). Semiconductors include ... (minerals, oxides, sulfides, germanium, silicon, selenium, fat, brine, blood, carbon).

3). The electrical capacity of a solitary conductor is calculated by the formula .... (C \u003d Q / φ).

4) ε 0 is ... (electrical constant and is equal to 8.85 * 10 -12 C 2 / N * m 2).

5) Electric capacity is measured in ... (farads).

6) The electrical capacitance of the sphere depends ... (on the radius).

7) What three groups divide all substances ... (conductor, semiconductor, dielectric).

Option 2.

1) A semiconductor is a substance in which ... (the number of free charges depends on external conditions).

2) Conductors include ... (metals. Solutions of salts, alkalis, acids, moist air, plasma, human body).

3) The electrical capacity of a solitary ball is calculated by the formula ... (C = 4π ε 0 ε R).

4) ε is ... (dielectric constant of the medium)

5) The charge is measured in ... (coulombs).

6) The electrical capacity of the sphere does not depend on ... (the charge on its surface).

7) Dielectrics include ... (gases, distilled water, benzene, oils, glass, porcelain, mica, wood, and others).

Learning new material.

(during the review, a supporting abstract is filled out).

A device called a capacitor is used to store electrical charges.

What is a capacitor? What does it consist of?

Basic outline.

A capacitor is ... (a system of two conductors separated by a dielectric layer, the thickness of which is small compared to the dimensions of the conductor).

Conductors are ... (capacitor plates).

Capable of accumulating a large charge.

Symbol:

Electric field inside a capacitor.

In order to charge .... (attach its plates to the poles of the current source).

Types of capacitors: air, mica, ceramic, paper, electrolytic, ...

(table display: Types of capacitors).

Message: first capacitor.

The main characteristic is electrical capacity.

Electric capacity is .. (a physical quantity that characterizes the ability of two conductors to accumulate an electric charge).

Show animation on the computer: "The capacity of the capacitor and its use."

C = q / φ; C = εε 0 S / d.

Unit of measure: Farad (F).

Application:

radio engineering;

camera flash;

computer keyboard;

Capacitor energy.

(Animation: "Construction and Energy of a Capacitor").

Types of connections in the diagram:

C \u003d C 1 + C 2 + ... ... ..

1 / C \u003d 1 / C 1 + 1 / C 2 + ....

Flaws:

Energy does not last long.

Discharges quickly.

Constant recharging is required.

1. Problem solving.

The capacitor has an electric capacitance C = 5pF. What charge was on each of its plates, if the potential difference between them is U = 100 V.

The charge q \u003d 6 * 10 -4 C on the plates of a flat capacitor creates a potential difference between the plates of 200 V. Determine the capacitance of the capacitor. (Kasyanov: Physics -10, p. 403, task No. 1).

Calculate the energy of the electrostatic field of a 0.1 μF capacitor charged to a potential difference of 200V. (Kasyanov: Physics - 10, p. 406, task No. 1).

Find the electric capacitance of a flat capacitor, if the area of ​​​​each of its plates is 1m 2, the distance between the plates is 1.5 mm. The dielectric is mica (ε = 6).

Independent work.

(after completion, they check with each other)

1 option.

1. What is the capacitance of a capacitor if, when it is charged to a voltage of 1.4 kV, it receives a charge of 28 nC?

2. Calculate the energy of the capacitor of the starting motor at the moment of its complete discharge, if it is known that the voltage on the plates is 300 V, and the capacitance of the capacitor is 0.25 μF.

Option 2.

1. Find the capacitance of an air capacitor charged to a potential difference of 200 V. The area of ​​each plate is 0.25 m 2, the distance between them is 1 mm. (ε = 1).

2. The capacitor says 4 uF, 100 V. What is the maximum energy it can have.

Summing up the lesson. Grading.

What have you learned? What have you learned?

Repeat the basic concepts. (capacitor, plates, capacitance, energy, application).

Homework.

Learn the baseline.

Solve a problem.

Task: The area of ​​each of the plates of a flat capacitor is 200 cm 2 , and the distance between them is 1 cm. What is the field energy if the field strength is 500 kV/m?