"Charge of the electric field" - When electrified, electrons move from one body to another. Tension vector electric field created by two identical charges at point C, directed ... 1) Left 2) Down 3) Up 4) Right. In the second conductor, when moving the same charge, the electric field does the work of 40 J. There is no attraction-repulsion interaction.

"Strength and potential of the electric field" - Why does a shark quickly detect a person in the water? Lesson objectives: Why does a shark quickly find a person who has fallen into the water? Some practical examples of the application of the main characteristics of the electric field. The distance between the cloud and the earth is 2 km. Repetition. A potential difference of 4 GV arose between the cloud and the Earth.

"Electric charge of the body" - The law of conservation of charge 1.2. Interaction of electric charges in vacuum. Question and early delivery exams 651 - 750 - three!!! The law of conservation of charge. Therefore, the energy of electrostatic interaction is potential energy. Questions and passing the exam only at the appointed time, i.E. Scheduled.

"Field Potential" - Potential electrostatic field. The potential value is considered relative to the selected zero level. All points inside the conductor have the same potential (=0). Any electrostatic field is potential. On a closed trajectory, the work of the electrostatic field is 0. Properties. The tension inside the conductor \u003d 0, which means that the potential difference inside \u003d 0.

"Electric field and its intensity" - Electric field lines start on positive charges and end on negative ones. Tension lines for two plates. Acts on electric charges with some strength. According to Faraday's idea, electric charges do not act directly on each other. "Electric field. What are the types of electric charges?

"Electric field strength" - The unit of voltage in the SI system: [ U ] \u003d 1 B 1 Volt is equal to electrical voltage in the section of the circuit where, with the flow of a charge equal to 1 C, work is performed equal to 1 J: 1 V \u003d 1 J / 1 C. In 1979, the highest voltage was obtained in the USA in laboratory conditions. Voltage characterizes the electric field created by the current.

There are 10 presentations in total in the topic

5. Electrostatics

Coulomb's law

1. Charged bodies interact. In nature, there are two types of charges, they are conditionally called positive and negative. Charges of the same sign (like) repel, charges of opposite signs (opposite) attract. The unit of charge in the SI system is the coulomb (denoted

2. In nature, there is a minimum possible charge. He is called

elementary and denoted by e . The numerical value of the elementary charge e ≈ 1.6 10–19 C, Electron charge q electr = –e, proton charge q proton = +e. All charges

in nature are multiples of the elementary charge.

3. In electrically isolated system the algebraic sum of the charges remains unchanged. For example, if you connect two identical metal balls with charges q 1 \u003d 5 nCl \u003d 5 10–9 C and q 2 \u003d - 1 nC, then the charges will be distributed

between the balls equally and the charge q of each of the balls becomes equal

q \u003d (q 1 + q 2) / 2 \u003d 2 nC.

4. A charge is called a point charge if its geometric dimensions are much smaller than the distances at which the effect of this charge on other charges is studied.

5. Coulomb's law determines the magnitude of the force electrical interaction two fixed point charges q 1 and q 2 located at a distance r from each other (Fig. 1)

Here F 12 is the force acting on the first charge from the second, F 21 is the force,

acting on the second charge from the side of the first, k ≈ 9 10 9 N m2 /Cl2 is a constant in Coulomb's law. In the SI system, this constant is usually written as

k = 4 πε 1 0 ,

where ε 0 ≈ 8.85 10 − 12 F/m is the electrical constant.

6. The force of interaction of two point charges does not depend on the presence of other charged bodies near these charges. This statement is called the principle of superposition.

Electric field strength vector

1. Place a point charge q near a motionless charged body (or several bodies). We will assume that the magnitude of the charge q is so small that it does not cause the movement of charges in other bodies (such a charge is called a trial charge).

From the side of a charged body, a force F will act on a stationary test charge q. In accordance with Coulomb's law and the principle of superposition, the force F will be proportional to the magnitude of the charge q. This means that if the value of the test charge is increased, for example, by 2 times, then the value of the force F will also increase by 2 times, if the sign of the charge q is reversed, then the force will change direction to the opposite. This proportionality can be expressed by the formula

F = qE.

The vector E is called the electric field strength vector. This vector depends on the distribution of charges in the bodies that create the electric field, and

on the position of the point at which the vector E is defined in the indicated way. We can say that the electric field strength vector equal to strength acting on a unit positive charge placed in given point space.

The definition of E G = F G /q can also be generalized to the case of variable (time-dependent) fields.

2. Calculate the electric field strength vector created by a fixed point charge Q . Let us choose some point A located at a distance r from point charge Q. To determine the intensity vector at this point, we mentally place a positive test charge q in it. On the

a test charge from a point charge Q will act as an attractive or repulsive force, depending on the sign of the charge Q. The magnitude of this force is

F = k| Q| q. r2

Therefore, the modulus of the electric field strength vector created by a fixed point charge Q at a point A remote from it at a distance r is equal to

E = k r |Q 2 |.

The vector E G starts at point A and is directed from the charge Q if Q > 0 and to the charge Q ,

if Q< 0 .

3. If the electric field is created by several point charges, then the intensity vector at an arbitrary point can be found using the principle of superposition of fields.

4. Force line (vector line E ) is called a geometric line,

the tangent to which at each point coincides with the vector E at this point.

In other words, the vector E is directed tangentially to the line of force at each of its points. The line of force is assigned a direction - along the vector E. Painting lines of force is a visual image of the force field, gives an idea of ​​the spatial structure of the field, its sources, allows you to determine the direction of the intensity vector at any point.

5. A field is called a uniform electric field, vector E which is the same (in magnitude and direction) at all points. Such a field is created, for example, by a uniformly charged plane at points located fairly close to this plane.

6. The field of a sphere uniformly charged over the surface is zero inside the sphere,

a outside the ball coincides with the field of a point charge Q located in the center of the ball:

where Q is the charge of the ball, R is its radius, r is the distance from the center of the ball to the point, in

which defines the vector E .

7. In dielectrics, the field is weakened. For example, a point charge or a sphere uniformly charged over the surface, immersed in oil, creates an electric field

E = k ε |r Q 2 |,

where r is the distance from the point charge or the center of the ball to the point at which the intensity vector is determined, ε is the dielectric constant of the oil. The dielectric constant depends on the properties of the substance. The dielectric constant of vacuum ε = 1, the dielectric constant of air is very close to unity (when solving problems, it is usually considered equal to 1), for other gaseous, liquid and solid dielectricsε > 1.

8. When the charges are in equilibrium (if there is no orderly movement of them), the electric field strength inside the conductors is zero.

Work in an electric field. Potential difference.

1. The field of fixed charges (electrostatic field) has an important property: the work of the forces of the electrostatic field to move the test charge from some point 1 to point 2 does not depend on the shape of the trajectory, but is determined only by the positions of the start and end points. Fields with this property are called conservative. The property of conservatism allows you to determine the so-called potential difference for any two points of the field.

Potential differenceϕ 1 − ϕ 2 at points 1 and 2 is equal to the ratio of the work A 12 of the field forces to move the test charge q from point 1 to point 2 to the value of this charge:

ϕ1 - ϕ2 =A q 12 .

Such a definition of the potential difference makes sense only because the work does not depend on the shape of the trajectory, but is determined by the positions of the initial and final points of the trajectories. In the SI system, the potential difference is measured in volts: 1V = J / C.

Capacitors

1. The capacitor consists of two conductors (they are called plates), separated from one another by a dielectric layer (Fig. 2), and the charge of one

plates Q, and the other -Q. The charge of the positive plate Q is called the charge of the capacitor.

2. It can be shown that the potential difference ϕ 1 − ϕ 2 between the plates is proportional to the charge Q, that is, if, for example, the charge Q is increased by 2 times, then the potential difference will increase by 2 times.

ε S

ϕ 1ϕ 2

Fig.2 Fig.3

This proportionality can be expressed by the formula

Q \u003d C (ϕ 1 -ϕ 2),

where C is the coefficient of proportionality between the charge of the capacitor and the potential difference between its plates. This coefficient is called the capacitance or simply the capacitance of the capacitor. The capacitance depends on the geometric dimensions of the plates, their relative position and permittivity environment. The potential difference is also called voltage, which is denoted U. Then

Q=CU.

3. A flat capacitor consists of two flat conductive plates located parallel to each other at a distance d (Fig. 3). This distance is assumed to be small compared to the linear dimensions of the plates. The area of ​​\u200b\u200beach plate (capacitor lining) is equal to S, the charge of one plate is Q, and the other is Q.

At some distance from the edges, the field between the plates can be considered uniform. Therefore ϕ 1 -ϕ 2 = Ed, or

U = Ed.

The capacitance of a flat capacitor is determined by the formula

C = εε d 0 S ,

where ε 0 \u003d 8.85 10–12 F / m is the electrical constant, ε is the permittivity of the dielectric between the plates. From this formula it can be seen that in order to obtain a large capacitor, it is necessary to increase the area of ​​​​the plates and reduce the distance between them. The presence between the plates of a dielectric with a high permittivity ε also leads to an increase in capacitance. The role of the dielectric between the plates is not only to increase the dielectric constant. It is also important that good dielectrics can withstand a high electric field without allowing breakdown between the plates.

In the SI system, capacitance is measured in farads. A one farad flat capacitor would be gigantic. The area of ​​each plate would be approximately equal to 100 km2 with a distance between them of 1 mm. Capacitors are widely used in engineering, in particular, for the accumulation of charges.

4. If the plates of a charged capacitor are closed with a metal conductor, then a electricity and the capacitor will discharge. When a current flows in a conductor, a certain amount of heat is released, which means that a charged capacitor has energy. It can be shown that the energy of any charged capacitor (not necessarily a flat one) is given by

W = 1 2 CU2 .

Considering that Q = CU , the energy formula can also be rewritten as

W \u003d Q 2 \u003d QU.