5. Elektrostatics
The law of Kulon.
1. Charged bodies interact. In nature there are two types of charges, they are conventionally called positive and negative. The charges of one sign (the same name) are repelled, the charges of opposite signs (different) are attracted. Unit of charges of charges in the system SI - pendant (designated
2. In nature, there is a minimum possible charge. He's called
elementary and denote e. The numerical value of the elementary charge is ≈ 1.6 10-19 CL, the electron charge is electr \u003d -e, the proton proton charge \u003d + e. All charges
in nature is painted elementary charge.
3. In an electrically isolated system, the algebraic amount of charges remains unchanged. For example, if you connect two identical metal balls with chargesq 1 \u003d 5 NL \u003d 5 10-9 CL andQ 2 \u003d - 1 ND, then charges will be distributed
between the balls row and the charge q each of the balls will become equal
q \u003d (Q 1 + Q 2) / 2 \u003d 2 ND.
4. The charge is called point if its geometrical dimensions are significantly less than the distances in which the action of this charge on other charges is being studied.
5. The law of Culon determines the amount of power of the electrical interaction of two fixed point chargesq 1 andq 2, located at a distance from each other (Fig. 1)
k | Q | | Q. | ||||||
F \u003d | F. | | \u003d | F | |||||
Here F 12 - force acting on the first charge from the second side, F 21 - force,
activating on the second charge from the side of the first, k ≈ 9 10 9 N M2 / CL2 is constant in the law of the coulon. In this system, this constant is customary to record as
k \u003d 4 πε 1 0,
where ε 0 ≈ 8.85 10 - 12 F / M is the electrical constant.
6. The strength of the 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. Position near a fixed charged body (or several bodies) Dot charge Q. We assume that the charge rate is so small that it does not cause the movement of charges in other bodies (such a charge is called trial).
From the charged body on the stationary test charge q will act power. In accordance with the Culon law and the principle of superposition, force will be proportional to the value of the charge. This means that if the value of the test charge is increased, for example, 2 times, then the value of the power will also increase by 2 times, if the charge is changed to the opposite, then the force will change the direction to the opposite. Such proportionality can be expressed by the formula
F \u003d QE.
Vector E is called tension vector electric field. This vector depends on the distribution of charges in bodies creating electric field, I.
from the position of the point in which the vector E is defined by the specified method. We can say that the vector of electric field strength equal to poweracting on a single positive charge placed at this point of space.
Definition E G \u003d F G / Q can be generalized in case of variables (depending on time) fields.
2. Calculate the vector of electric field strength created by a fixed point charge Q. Choose some point, located at a distance from point chargeQ. To determine the vector of tension at this point, mentally put a positive test charge in it. On the
trial charge from the side charge Q will act the force of attraction or repulsion depending on the charge sign. The magnitude of this force is equal
F \u003d k | Q | q. R2
Consequently, the module of the electric field strength vector created by a fixed point charge Q at a point removed from it to the distanceR is equal to
E \u003d k R | Q 2 |.
The vector E G begins at point and directed from chargeq, ifQ\u003e 0, and to the charge,
if Q.< 0 .
3. If the electrical field is created by several point charges, the vector of tension at an arbitrary point can be found using the principle of the superposition of fields.
4. Power line (vector lineE) refer to the geometric line,
the tangent to which at each point coincides with the vector E at this point.
In other words, the vector E is aimed at a tangent of the power line at each point. The power line is attributed to the direction - along the vector. Picture silest lines is a visual manner power fieldIt gives an idea of \u200b\u200bthe spatial field structure, its sources, allows you to determine the direction of the tension vector at any point.
5. Uniform electric field called field, vectorE of which the same (largest and direction) at all points. This field creates, for example, a uniformly charged plane at points located close enough of this plane.
6. The field is uniformly charged over the ball surface equals zero inside the ball,
but outside a bowl coincides with a point charge fieldQ, located in the center of the ball:
k | Q | | r\u003e R | ||
E \u003d R2. | |||
at R.< R | |||
where Q is the ball of the ball, R is its radius, R is the distance from the center of the ball to the point, in
which is determined by the vector E.
7. In dielectrics, the field is weakened. For example, a point charge or uniformly charged on the surface of the ball, immersed in the oil, create an electric field
E \u003d k ε | R Q 2 |,
where R is the distance from the point charge or center of the ball to the point in which the vector of tension is determined, ε is the dielectric permeability of the oil. Dielectric constant depends on the properties of the substance. The dielectric permeability of the vacuumε \u003d 1, the dielectric permeability of the air is very close to one (when solving problems, it is usually considered to be 1), for other gaseous, liquid and solid dielectricsε\u003e 1.
8. When equilibrium charges (if there are no ordered movement), the electric field strength inside the conductors is zero.
Work in the electric field. Potential difference.
1. Field of fixed charges (electrostatic field) has an important property: work forces electrostatic field To move the test charge from a certain point 1 to point 2, it does not depend on the form of the trajectory, but is determined only by the provisions of the initial and endpoint. Fields possessing such a property are called conservative. The properties of conservatism allows you to determine the so-called potential difference for two of any field points.
Potential differenceΦ 1 -φ 2 at points 1 and 2 is equal to the ratio of the operation of the 12 forces for the movement of the test charge q from point 1 to the point of 2 kbelichine, charge:
φ1 - φ2 \u003d A Q 12.
Such a determination of the potential difference makes sense only because the work does not depend on the form of the trajectory, but is determined by the provisions of the initial and endpoint of the trajectories. In the system, the potential difference is measured in volts: 1B \u003d J / CL.
Condencators
1. The capacitor consists of two conductors (they are called plates) separated by one from the other layer of dielectric (Fig. 2), and the charge of one
plugs q, and the other -Q. The charge of positive cover is called a capacitor charge.
2. It can be shown that the difference in the potentials φ 1 -φ 2 between the plates is proportional to the value of chargeq, that is, if, for example, the charge is increased by 2 times, then the potential difference will increase by 2 times.
ε S.
φ 1φ 2.
Fig.2 Fig.3
Such 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 electrical capacity or simply capacitance of the condenser. Capacity depends on the geometric sizes of the plates, their mutual location and dielectric permeability medium. The potential difference is also called a voltage that is denoted. Then
Q \u003d Cu.
3. The flat capacitor is two flat conductive plates located in parallel to each other at d (Fig. 3). This distance is assumed to be small compared to the linear dimensions of the plates. The area of \u200b\u200beach plate (condenser clamp) is equal, the charge of one plateq, and the other -Q.
At some distance from the edges, the field between the plates can be considered homogeneous. Therefore, φ 1 -φ 2 \u003d ED, or
U \u003d ED.
The container of the flat capacitor is determined by the formula
C \u003d εε d 0 s,
where ε 0 \u003d 8.85 10-12 f / m is the electrical constant, ε is the dielectric permeability of the dielectric between the plates. From this formula, it can be seen that to obtain a capacitor of a large capacity, it is necessary to increase the area of \u200b\u200bthe plates and reduce the distance between them. The presence between dielectric plates with a large dielectric constantε also leads to an increase in capacity. The role of a dielectric between the plates consists not only in increasing the dielectric constant. It is also important that good dielectrics can withstand a high electric field, not allowing a breakdown between the plates.
In the system, the container is measured in the Faradays. The flat capacitor in one Faraday would have gigantic sizes. The area of \u200b\u200beach plate would be approximately 100 km2 at a distance between them 1 mm. Capacitors are widely used in the technique, in particular, for accumulation of charges.
4. If the charged condenser is plated to close the metal conductor, then the conductor will arise electricity And the capacitor is discharged. When current flows in the conductor, a certain amount of heat is selected, which means that the charged condenser has energy. It can be shown that the energy of any charged condenser (not necessarily flat) is determined by the formula
W \u003d 1 2 Cu2.
Considering that Q \u003d Cu, the energy formula can also be rewritten as
W \u003d Q 2 \u003d QU.
"Electric field charge" - when electrification, electrons go from some bodies to others. The vector of electric field strength created by two identical charges at the point C, directed ... 1) left 2) down 3) up 4) to the right. In the second conductor, when moving the same charge, the electric field makes the operation of 40 J. Attraction repelling the interaction is absent.
"The tension and potential of the electric field" - why the shark quickly detects a person in water? Objectives of the lesson: Why does Shark quickly detect a person who has fallen into the water? Some practical examples of the use of the main characteristics of the electric field. Distance between the cloud and land is 2 km. Reiteration. Between the cloud and the earth there was a difference in potentials of 4 gv.
"Electric charge of the body" - the law of saving charge 1.2. The interaction of electrical charges in vacuo. Question and early passing exams 651 - 750 - three !!! The law of saving charge. Consequently, the energy of electrostatic interaction - potential energy. Questions and passing the exam only on a designated period, i.e. Scheduled.
The "field potential" is the potential of the electrostatic field. The magnitude of the potential is considered relative to the selected zero level. All points inside the conductor have the same potential (\u003d 0). Every electrostatic field is potentially. On a closed trajectory, the operation of the electrostatic field is 0. Properties. The tension inside the conductor \u003d 0, which means the difference of potentials inside \u003d 0.
"Electrical field and its tension" - the line of the electric field begin on positive charges And ends on negative. Line of tension for two plates. Acts on electric charges With some force. According to the idea of \u200b\u200bFaraday, electrical charges do not act on each other directly. "Electric field. What are the types of electrical charges?
"Electric field strength" - a unit of measurement of the voltage in the SI system: [u] \u003d 1 b 1 volt is equal electric tension On the section of the chain, where when the charge of the charge, equal to 1 CL, is performed, equal to 1 J: 1 V \u003d 1 J / 1 CL. In 1979, the highest voltage was obtained in the USA in laboratory conditions. The voltage characterizes the electric field created by the current.
Total in the subject of 10 presentations
