Далее Лаб 2.1 и 3.4
Абзац отступ 1,25
Формулы 14 дпи
Надписи к рисункам 12 дпи
Нумерация разделов и рисунков
Тире – длинные
LABORATORY WORK № 2-1
1. Topic: STUDYING OF ELECTROSTATIC FIELD
2. Goal of the work:
2.1. Study the main characteristics of electrostatic field: intensity, potential and relation between them.
2.2. Investigation of electrostatic field with the help of equipotential surfaces.
3. Main concepts
3.1 Electric field. Electric intensity
Electric charges interact, when they are on different distances one from another. This interaction happens with the help of electrical field, which exists around every charge, inseparable connected with the charge and fill all the space. Electrical field - is a particular type of the matter. Its main property is in that the force acts on every charge placed in this field. The field of immovable charges called electrostatic. The section of physics, which studies immovable charges and their fields, called electrostatics.
There exists another kind of interaction of electrical charges – magnetic. Magnetic field side by side with electrical exists around moving charges. Around immovable charges magnetic field is absent. Magnetic fields will be considered in the section ''Electromagnetism''.
The main law of electrostatics is the Coulomb law: the force of interaction of two point charges directly proportional to the product of their quantities q1 and q2 and inversely proportional to the square of distance r between them:
,
(1)
where ε – relative permittivity of medium, which shows on how many times the force of interaction of charges in the medium less, than in vacuum; ε – is the dimensionless quantity.
Proportionality coefficient k in the SI system
,
where 0=8,8510–12 F/m – electric constant or dielectric permittivity of vacuum.
In the SI system the Coulomb law is signed up as
,
(2)
where 0 - is an absolute dielectric permittivity of medium.
The force of interaction of two point charges directed along the straight line, which joins these charges. The point charges have a sizes that appreciably smaller, than distances between them.
The electrostatic field explores with help of test charge q that is such charge, the introduction of which does’’t change the exploring field. If we put a different test charges in the same point of the field, then different in-value forces will act on them. But the force-to-charge ratio for this point will be the constant quantity. This ratio is a force characteristic of field and is called electric intensity E.
Electric
intensity
in the given point – is the vector quantity, which equals to force
that
actied on a unit positive test charge
in this point of the field.
;
.
(3)
In the SI system electric intensity is measured in V/m (Volts per meter). From formula (3), we can see, that V/m= N/C (Newton per Coulomb).
Electric
field vector
has the same direction as electric force that actied on a unit
positive test charge.
а)
b)
Fig.
1 – Electric
intensity
vectors
of
а)
positive
and
b)
negative
charges
and
are directed from the charge along divergent rays.
On
the Fig. 1,b
are represented vectors
and
in the points C
and D
of the field of the negative charge q2.
Both vectors are directed to the charge along converging rays.
Substituting (2) in (3) we obtain electric intensity of the point charge q on the distance r from it
.
(4)
Fig.
2
– Resultant electric
intensity
vector
vectors
of
two charges
defines as vector sum of electric intensity vectors, created by every
charge separately. For example, on the Fig. 2 the fields of chargesq1
(positive) and q2
(negative) is being overlapped in the point A. Vector of intensity
directed from the charge q1,
as in the case of absence of charge q2.
Similar vector of intensity
directed from the charge q1,
as in the case of absence of charge q1.
Electric intensity vector direction of resultant field defines according to the parallelogram rule (see Fig. 2). Its numerical value calculates by the cosine theorem:
.
(5)
Electrostatic force, with which any electrostatic field E acted on charge q defines by the formula
.
(6)