Algebraic sum of charges.

z:\Program Files\Physicon\Open Physics 2.5 part 2\content\chapter1\section\paragraph2\theory.htmlz:\Program Files\Physicon\Open Physics 2.5 part 2\content\chapter1\section\paragraph2\theory.htmlz: \Program Files\Physicon\Open Physics 2.5 part 2\design\images\ring_h.gifq 1 +q 2 +q 3 + +q n = const. (1.1)

The law of conservation of electric charge states that in a closed system of bodies processes of creation or disappearance of charges of only one sign cannot be observed. The presence of charge carriers is a condition for the body to conduct electricity. Depending on their ability to conduct electric current, bodies are divided into: conductors, dielectrics and semiconductors.

Conductors– bodies in which an electric charge can move throughout its entire volume. Conductors are divided into two groups:

1) conductors first kind(metals) – the transfer of electrical charges (free electrons) into them is not accompanied by chemical transformations;

2) conductors second kind(molten salts, solutions of salts and acids, and others) - the transfer of charges (positively and negatively charged ions) into them leads to chemical changes.

Dielectrics(glass, plastic) - bodies that do not conduct electric current and have practically no free charges.

Semiconductors– occupy an intermediate position between conductors and dielectrics. Their conductivity strongly depends on external conditions (temperature, ionizing radiation etc.). In the International SI System, the unit of charge is taken to be pendant(Cl)

Electric charge passing through a cross section

conductor at a current of 1 A for a time of 1 s.

z:\Program Files\Physicon\Open Physics 2.5 part 2\content\chapter1\section\paragraph2\theory.html z:\Program Files\Physicon\Open Physics 2.5 part 2\content\chapter1\section\paragraph2\theory.htmlz:\Program Files\Physicon\Open Physics 2.5 part 2\content\chapter1\section\paragraph2\theory.htmlz: \Program Files\Physicon\Open Physics 2.5 part 2\design\images\ring_h.gif 1.2. COULLOMB'S LAW.

Spot is a charge concentrated on a body whose linear dimensions are negligible compared to the distance to other charged bodies with which it interacts. The concept of a point charge, like a material point, is physical abstraction.

The forces of interaction between stationary charges are directly proportional to the product of the charge moduli and inversely proportional to the square of the distance between them: F = (1/4πεε 0)(q 1 q 2 /r 2), (1.2)

where ε 0 = 8.85 10 -12 (Cl 2 /N.m 2) is the electrical constant.

A quantity that shows how many times the force of interaction between charges in a vacuum is greater than in a medium is called dielectric constant of the medium ε .

Coulomb forces- central, i.e. they are directed along the line of connection of the center of charges. Interaction forces obey Newton's third law: F 1 = -F 2 . (1.3)

They are repulsive forces with the same signs of charges and attractive forces with different signs . The interaction of stationary electric charges is called electrostatic or Coulomb interaction. The branch of electrodynamics that studies the Coulomb interaction is called electrostatics.

ELECTROSTATIC FIELD.

ELECTROSTATIC FIELD STRENGTH.

According to modern concepts, electric charges do not act on each other directly. Each charged body creates an electric field in the surrounding space. This field exerts a force on other charged bodies. Thus, the interaction of charged bodies is carried out not by their direct influence on each other, but through the electric fields surrounding the charged bodies.

Tensions electric field called physical quantity, equal to the ratio of the force with which the field acts on a positive test charge placed at a given point in space to the magnitude of this charge:

E = F/q. (1.4).

Rice. 2. Field lines of Coulomb fields.

The direction of the tension vector coincides with the direction of the Coulomb force acting on the positive charge.

Graphically, the electrostatic field is depicted using tension lines - lines whose tangents at each point in space coincide with the direction of tension.

Magnitude dФ E = E n dS (1.5)

is called the flow of the tension vector through the area dS. For an arbitrary closed surface S vector flow E through this surface: Ф E = ò S E n dS, (1.6.)

where the integral is taken over the closed surface S.

Flow vector E is an algebraic quantity and depends not only on the field configuration E, but also on the choice of direction.

1.z:\Program Files\Physicon\Open Physics 2.5 part 2\design\images\Fwd_h.gifz:\Program Files\Physicon\Open Physics 2.5 part 2\design\images\Bwd_h.gifz:\Program Files\Physicon\ Open Physics 2.5 part 2\design\images\Fwd_h.gifz:\Program Files\Physicon\Open Physics 2.5 part 2\design\images\Bwd_h.gif4. PRINCIPLE OF SUPERPOSITION. ELECTROSTATIC FIELDS.

E = S E i . (1.7.)

According to the principle of superposition of electrostatic fields, the strength of the resulting field created by a system of charges is equal to geometric sum field strengths created at a given point by each of the charges separately E = S E i . (1.7.)

PROBLEMS OF ELECTROSTATICS.

The problems boil down to finding the field characteristics for a given arrangement of charges in space based on Coulomb's law and the principle of field superposition. In the case of continuous distribution of charges over bodies, they can be reduced to a system of point charges. To do this, it is enough to break charged bodies into infinitesimal parts.

DIPOLE FIELD.

Rice. 6. Dipole field.

An electric dipole is a system of two opposite point charges of equal magnitude. The vector directed along the axis of the dipole, from a negative charge to a positive charge and equal to the distance between them, is called the dipole arm l. Vector p = |q|.l (1.8)

coinciding in direction with the dipole arm and equal to the product of the charge and the arm, is called the electric moment of the dipole or dipole moment.

1) Field strength along the extension of the dipole axis at the point A. equal to

E A = E + - E - Marking the distance from the point A to the middle of the dipole through r, based on the Coulomb formula for vacuum, we obtain:

E = 1/(4pe 0) =

= q/(4pe 0)([(r + l/2) 2 - (r - l/2) 2 ]/ [(r - l/2) 2 (r + l/2) 2 ]) (1.9. )

according to the definition of a dipole, l/2<< r, That's why

E = 1/(4pe 0).(2ql/r 3) = 1/(4pe 0)(p/r 3). (1.10.)

2) Field strength at the perpendicular, restored to the dipole axis from its middle, at the point IN. Dot IN equidistant from the charges, therefore

E + = E - = 1/(4pe 0))