The energy of a charged capacitor application of capacitors presentation. Physics presentations "capacitors". Motivation of cognitive activity of students

12.08.2022

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 capacitance (capacity), which is denoted by the letter C. The capacitance is a physical quantity that characterizes the ability of two conductors to accumulate an 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.

Sections: Physics

Didactic goal

1. Give the concept of the electrical capacity of a solitary conductor and its unit; to acquaint with the device of a flat capacitor and the types of their connections.

2. Derive the formulas for the electrical capacity of a solitary conductor, a ball, a flat capacitor, a battery of capacitors connected in series and in parallel, and the energy of a charged capacitor.

3. Give a classification of capacitors depending on the type of dielectric that separates the plates, and the magnitude of the electric capacitance.

educational goal

Using the example of demonstrating the spark discharge of a capacitor or the discharge of a capacitor through an incandescent lamp, show that the electric field has energy, and therefore it is material.

Basic knowledge and skills

1. Know the physical meaning of electrical capacity, formulas for calculating the electrical capacity of a solitary conductor, a ball, a flat capacitor, a battery of parallel and series-connected capacitors and be able to apply them to solve problems.

2. Know the formula for calculating the energy of a charged capacitor and be able to apply it to solve problems.

The sequence of presentation of new material

1. Electrical capacity of the conductor. Units of electrical capacity.

2. The dependence of the electrical capacity of the conductor on its size, shape and surrounding bodies.

3. Electrical capacity of a metal ball (sphere).

4. Capacitors. Their device, purpose, charging and discharging, the role of the dielectric. Classification of capacitors.

5. Serial connection of capacitors in a battery.

6. Parallel connection of capacitors in a battery.

7. Energy of a charged capacitor. Volumetric energy density of the electric field.

Equipment

Two electrometers, four metal spheres (two diameters), an electrophore machine, two insulating stands, a demountable flat capacitor demo, a variable capacitance demo, a set of capacitors (ceramic, paper, mica, electrolytic), a flashlight, an electric lamp at 3.5 V and 0.28 A, DC source or AC powered rectifier, connection wires. Demonstrations

The dependence of the potential of a solitary conductor on the magnitude of the reported charge; the dependence of the potential of a solitary conductor on its size when the same charges are communicated; the dependence of the conductor potential on the presence of other conductors; the dependence of the electric capacitance of a flat capacitor on the area of the plate, the distance between the plates and the dielectric separating the plates; discharging a capacitor through an incandescent lamp or flash; device of various types of capacitors.

Motivation of cognitive activity of students

Nowadays, all students know about capacitors to some extent. Capacitors are widely used in radios, televisions, tape recorders and in many electronic devices. Capacitors are used to store electrical charges and electrical energy. The property of a capacitor to accumulate and store electrical charges is used in technology to obtain short-term current pulses of great strength. One example of this use of a capacitor is the electronic flash used in photography. In this case, the capacitor is discharged through a special lamp.

Lesson plan

Checking the knowledge, skills and abilities of students

1. Inform students of the results of the physical dictation performed in the last lesson; to analyze typical and blunders.

2. Orally interrogate four students on the following tasks:

Task one:

1) Explain the physical nature of electrostatic induction. Why is the voltage inside a conductor placed in an electric field zero?

2) Write the formula for the dependence of the strength and potential difference of a homogeneous electric field.

3) By how much will the average kinetic energy of the chaotic motions of gas molecules change with an increase in its temperature by 100 K? Answer. ∆E k \u003d 2.07 * 10 -21 J.

Task two:

1) Explain the physical nature of the polarization of non-polar dielectrics. Why is the strength inside a dielectric placed in an electric field less than the strength of the external field?

2) Write the formula for the electric field strength of a charged plane.

3) Determine the thermal energy of 3.2 kg of oxygen at a temperature of 127°C. Answer. ∆U=831 kJ.

Task three:

1) Explain the physical nature of the polarization of polar dielectrics. Why is an uncharged paper sleeve (dielectric) attracted to a charged body?

2) Write the formula for the potential of the electric field of a charged ball. 31 How much will the internal energy of 1.2 kg of carbon change when the temperature drops by 40°C? Answer. ∆U=49.86 kJ.

Task four:

1) In which dielectrics does the polarization not depend on temperature, and in which does it? Why?

2) Why, at equilibrium, the entire excess charge of an electrified conductor is located on its surface?

3) Determine the pressure of 2 kg of oxygen in a cylinder with a capacity of 0.4 m 3 at a temperature of 27°C. Answer,

p ≈ 0.39 MPa.

3. Check homework. Additional questions for the respondents:

T. No. 958. Electrify an ebonite stick by friction. First, just touch the electroscope ball, and then run the wand over it. Was the electroscope charged in the same way in both cases? (In the second case, the electroscope will be charged more, since the charge is removed not from one, but from many points on the surface of the stick.)

Vol. No. 974. What is the field strength at the center of a uniformly charged wire ring having the shape of a circle? At the center of a uniformly charged spherical surface? (In both cases, the intensity is 0.)

T. No. 986. In order to rarefy the electroscope, it is enough to touch it with your finger. Will the electroscope be discharged if there is a charged body isolated from the ground near it (no, because the charge of the opposite sign induced by the body will remain on the electroscope.)

T. No. 987. If a needle is brought to a charged “sultan” with a point, then the leaves of the sultan gradually begin to discharge. Why? (There is a charge of the opposite sign on the needle (of the same name goes into the ground on the hand), which neutralizes the charge on the leaves.)

How is Coulomb's law read?

How is the law of conservation of charge read?

What field is called an electric field?

Frontal survey

1. What is called the magnitude of the charge?

(The excess of electric charges of the same sign in any body is called the magnitude of the charge or the amount of electricity.)

2. How is the law of conservation of charge read?

(Electric charges do not arise and do not disappear, but are only redistributed among all the bodies participating in this or that phenomenon.)

3. What are the types of electrification?

4. Why, when pouring gasoline from one tank to another, it can ignite if special precautions are not taken?

(When gasoline flows out of a pipe, it becomes so electrified that an electric spark is created that ignites it.)

5. Read Coulomb's law?

6. Why are conductors for experiments on electrostatics made hollow?

(Because static charges are located only on the outer surface of the conductor.)

7. What do we call the dielectric constant of the medium? (The value characterizing the dependence of the interaction force between charges on the environment is called e s.)

8. Why do devices for electrostatic experiments do not have sharp ends, but end with rounded surfaces?

(At the sharp ends of the conductors, the density of charges is so high that they are not retained on the conductor and "drain" from it.)

9. What field is called an electric field?

(A field that transmits the action of one fixed electric charge to another fixed charge in accordance with Coulomb's law is called an electric field.)

10. What do we call the line of tension?

(This is such a line, tangent to each point of which the field strength vectors are directed.)

11. Properties of lines of force?

12. What field is called homogeneous?

13. How to determine the sign of the charge on the electroscope, having an ebonite stick and cloth?

(The sign of the charge of the electroscope will be negative if, from the touch of an electrified, ebonite stick, the leaves disperse at a larger angle.)

14. How will the force of interaction between two point charges change if the value of each charge is increased four times, and the distance between the charges is halved?

(Increase 64 times.)

15. What do we call the field potential of a given point? (The energy characteristic of the electric field at a given point is called the potential of the field at a given point.)

16. Formula for determining φ, E?

Analyze student responses, comment and say grades.

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1 option

The capacitance of two conductors is called...
The polarization of dielectrics is called...
The unit of electrical capacity is expressed in...

Option 2

Surfaces of equal potential are called...
The potential of an electrostatic field is called ...
The unit of electric field strength is expressed in ...

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Physical dictation.

1 option

The electrical capacitance of two conductors is the ratio of the charge of one of the conductors to the potential difference between this conductor and the neighboring one.

The polarization of dielectrics is called the displacement of positive and negative bound charges in opposite directions.

The unit of electrical capacity is expressed in farads (F).

Option 2

Surfaces of equal potential are called equipotential.

The potential of an electrostatic field is the ratio of the potential energy of a charge in the field to this charge.

The unit of electric field strength is expressed in volts per meter (V / m) or in newtons per pendant (N / C).

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3.04.07

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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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