The work done to move the charge is equal. The work of the electrostatic field. Potential. equipotential surfaces. Physical explanation of the potential

Forces act on electric charges in an electrostatic field. Therefore, if the charges move, then these forces do work. Calculate the work of the forces of a homogeneous electrostatic field when moving a positive charge q from a point A exactly B(Fig. 1).

per charge q, placed in a uniform electric field with intensity E, the force \(~\vec F = q \cdot \vec E \) acts. Field work can be calculated by the formula

\(~A_(AB) = F \cdot \Delta r \cdot \cos \alpha,\)

where ∆ r⋅cosα = AC = x 2 – x 1 = Δ x- projection of displacement onto the line of force (Fig. 2).

\(~A_(AB) = q \cdot E \cdot \Delta x. \ \ (1)\)

Consider now the movement of the charge along the trajectory ACB(see fig. 1). In this case, the work of a homogeneous field can be represented as the sum of works in the areas AC And CB:

\(~A_(ACB) = A_(AC) + A_(CB) = q \cdot E \cdot \Delta x + 0 = q \cdot E \cdot \Delta x\)

(Location on CB work is zero, because the displacement is perpendicular to the force \(~\vec F \)). As you can see, the field work is the same as when the charge moves along the segment AB.

It is not difficult to prove that the work of the field when moving a charge between points AB along any trajectory everything will be according to the same formula 1.

Thus,

• the work of moving a charge in an electrostatic field does not depend on the shape of the trajectory along which the charge moved q , but depends only on the initial and final positions of the charge.
• This statement is also true for an inhomogeneous electrostatic field.

Let's find work on a closed trajectory ABCA:

\(~A_(ABCA) = A_(AB) + A_(BC) + A_(CA) = q \cdot E \cdot \Delta x + 0 - q \cdot E \cdot \Delta x = 0.\)

The field, the work of forces of which does not depend on the shape of the trajectory and is equal to zero on a closed trajectory, is called potential or conservative.

Potential

It is known from mechanics that the work of conservative forces is associated with a change in potential energy. The system "charge - electrostatic field" has potential energy (energy of electrostatic interaction). Therefore, if we do not take into account the interaction of the charge with the gravitational field and environment, then the work done when moving a charge in an electrostatic field is equal to the change in the potential energy of the charge, taken with the opposite sign:

\(~A_(12) = -(W_(2) - W_(1)) = W_(1) - W_(2) . \)

Comparing the resulting expression with Equation 1, we can conclude that

\(~W = -q \cdot E \cdot x, \)

Where x is the charge coordinate on the 0X axis directed along the field line (see Fig. 1). Since the charge coordinate depends on the choice of the reference frame, the potential energy of the charge also depends on the choice of the reference frame.

If W 2 = 0, then at each point of the electrostatic field the potential energy of the charge q 0 is equal to the work that would be done by moving the charge q 0 from a given point to a point with zero energy.

Let an electrostatic field be created in some region of space by a positive charge q. We will place various test charges at some point of this field q 0 . Their potential energy is different, but the ratio \(~\dfrac(W)(q_0) = \operatorname(const)\) for a given point of the field serves as a characteristic of the field, called potential field φ at a given point.

• The potential of the electrostatic field φ at a given point in space is a scalar physical quantity equal to the ratio of potential energy W, which has a point charge q at a given point in space, to the value of this charge:

The SI unit of potential is volt(V): 1 V = 1 J/C.

• Potential is the energy characteristic of the field.

Potential properties.

• The potential, like the potential energy of the charge, depends on the choice of reference system (zero level). IN technique for the zero potential choose the potential of the surface of the Earth or a conductor connected to the ground. Such a conductor is called grounded. IN physics for the reference point (zero level) of the potential (and potential energy) is taken any point infinitely distant from the charges that create the field.

• On distance r from a point charge q, which creates a field, the potential is determined by the formula

• Potential at any point of the field created positive charge q, positive, and the field created by the negative charge is negative: if q> 0, then φ > 0; If q < 0, то φ < 0.

• The potential of the field formed by a uniformly charged conducting sphere with a radius R, at a point at a distance r from the center of the sphere \(~\varphi = k \cdot \dfrac(q)(R)\) for r ≤ R and \(~\varphi = k \cdot \dfrac(q)(r)\) with r > R .

• Superposition principle: the potential φ of the field created by the system of charges at some point in space is equal to the algebraic sum of the potentials created at this point by each charge separately:

Knowing the potential φ of the field at a given point, it is possible to calculate the potential energy of the charge q 0 placed at this point: W 1 = q 0 ⋅φ. If we assume that the second point is at infinity, i.e. W 2 = 0, then

\(~A_(1\infty) = W_(1) = q_0 \cdot \varphi_1 .\)

Potential charge energy q 0 at a given point of the field will be equal to the work of the forces of the electrostatic field to move the charge q 0 from a given point to infinity. From the last formula we have

\(~\varphi_1 = \dfrac(A_(1\infty))(q_0).\)

• The physical meaning of the potential: the potential of the field at a given point is numerically equal to the work of moving a unit positive charge from a given point to infinity.

Potential charge energy q 0 placed in an electrostatic field of a point charge q on distance r From him,

\(~W = k \cdot \dfrac(q \cdot q_0)(r).\)

• If q And q 0 - like charges, then W> 0 if q And q 0 - charges of different sign, then W < 0.

• Note that this formula can be used to calculate the potential energy of the interaction of two point charges if for zero value W its value is chosen at r = ∞.

Potential difference. Voltage

The work of the forces of the electrostatic field on the movement of the charge q 0 from point 1 exactly 2 fields

\(~A_(12) = W_(1) - W_(2) .\)

We express the potential energy in terms of the field potentials at the corresponding points:

\(~W_(1) = q_0 \cdot \varphi_1 , W_(2) = q_0 \cdot \varphi_2 .\)

\(~A_(12) = q_0 \cdot (\varphi_1 - \varphi_2) .\)

Thus, the work is determined by the product of the charge and the potential difference of the initial and final points.

From this formula, the potential difference

\(~\varphi_1 - \varphi_2 = \dfrac(A_(12))(q_0) .\)

• Potential difference is a scalar physical quantity, numerically equal to the ratio of the work of the field forces to move the charge between the given points of the field to this charge.

The SI unit for potential difference is the volt (V).

• 1 V is the potential difference between two such points of the electrostatic field, when moving between which a charge of 1 C is done by the field forces, work of 1 J is performed.

The potential difference, unlike the potential, does not depend on the choice of the zero point. The potential difference φ 1 - φ 2 is often called electric voltage between given points of the field and denote U:

\(~U = \varphi_1 - \varphi_2 .\)

• Voltage between two points of the field is determined by the work of the forces of this field to move a charge of 1 C from one point to another.

The work of the electric field forces is sometimes expressed not in joules, but in electronvolts.

• 1 eV is equal to the work done by the field forces when moving an electron ( e\u003d 1.6 10 -19 C) between two points, the voltage between which is 1 V.

Potential difference and tension

Calculate the work done by the forces of the electrostatic field when moving an electric charge q 0 from a point with potential φ 1 to a point with potential φ 2 of a uniform electric field.

On the one hand, the work of the field forces \(~A = q_0 \cdot (\varphi_1 - \varphi_2)\).

On the other hand, the work of moving the charge q 0 in a uniform electrostatic field \(~A = q_0 \cdot E \cdot \Delta x\).

Equating the two expressions to work, we get:

\(~q_0 \cdot (\varphi_1 - \varphi_2) = q_0 \cdot E \cdot \Delta x, \;\; E = \dfrac(\varphi_1 - \varphi_2)(\Delta x),\)

where ∆ x- projection of displacement onto the line of force.

This formula expresses the relationship between the intensity and the potential difference of a uniform electrostatic field. Based on this formula, you can set the unit of tension in SI: volt per meter (V/m).

Literature

1. Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Proc. allowance for institutions providing general. environments, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsia i vykhavanne, 2004. - C. 228-233.
2. Zhilko, V. V. Physics: textbook. allowance for the 11th grade. general education institutions with Russian. lang. training with a 12-year term of study (basic and elevated levels) /IN. V. Zhilko, L. G. Markovich. - 2nd ed., corrected. - Minsk: Nar. asveta, 2008. - S. 86-95.

An electric field is a vector diagram of a field that occurs near electrically charged bodies and particles when the electromagnetic field changes. Such a phenomenon as the work of an electrostatic field when moving a charge in a conductor cannot be seen. It can be traced when exposed to charged bodies. That is, in order for it to appear, it is necessary to apply an electric charge to them. The main parameters of an electrically charged field are voltage, potential and intensity.

Physical explanation of the potential

On plain language Potential is the act of moving a body from its initial location to its final location. In an electric field, this is the energy that moves an electron; as a result, it moves from a point of zero potential to another point that has a potential that is not equal to zero.

The higher the potential spent on the movement of the charge, the greater the flux density per unit area. This phenomenon can be compared with the law of gravity: the greater the weight, the higher the energy, and, therefore, the significant density of the gravitational field.

In nature, there are charges with an insignificant potential and with a low degree of density, as well as charged particles with a high potential and a saturated flux density. Such a phenomenon as the work of moving a charge is observed during a thunderstorm, when electrons are depleted in one place, and they are saturated in another, forming such an electrically charged field when a lightning discharge occurs.

The formation of an electric field and its features

An electric field is formed in such cases:

• with changes in the electromagnetic field (for example, with electromagnetic oscillations);
• when charged particles appear.

An electrically saturated field exerts a certain energy effect on charged particles. But this force is not capable of accelerating charged bodies in space. In addition, they are affected by the energy of the magnetic field.

The work of an electrostatic field is easily observed in a domestic setting. To do this, just take some dielectric material and rub it against the wool. For example, take a plastic pen and rub it against your hair. The result of this action will be the formation of an electric field around the handle and the appearance of a charge.

From this we can conclude that an electrically saturated field is a characteristic state of matter. Its main function is a force effect on a charged particle. In addition, it has the following properties:

• gains strength with increased charge;
• acts on charged particles with a certain force and has no boundaries;
• is detected in the process of impact on the charged part of matter.

If the charges are not mobile, then such an electrically charged field is called electrostatic. Its main property is a charged state that does not change in time, since the field is formed due to charged bodies (example with a pen and hair).

The concept of a homogeneous electric field

A uniform electrically charged field is created between two flat plates with opposite charges. Their lines of tension have a parallel structure.

Due to the symmetrical property, the electric field exerts the same force on the charged particles. The work of such an electric field can be measured without any dependencies.

Energy for moving a positively charged particle

An electrically saturated field can be called an avalanche of charged particles from plus to minus. This movement creates a high degree tension in the flow area. A flow is a set of features of the movement of electrons passing inside an electric field. Charged particles always move from the positively charged pole to the negatively charged pole.

The intensity of the effect of the field on the charge in any area is determined by the force acting on the charged particle placed in this area of ​​the electrically charged field. The work itself consists in the energy expended to move the charge in the structure of the conductor. This action can be found using Ohm's law.

When moving a charge in an electric field, it is in different areas:

• remains unchanged;
• decreases;
• increases.

The energy of an electrically saturated field and the potential of a particle with a certain charge is proportional to the level of the charge itself. The ratio of the potential of a charged particle to its charge is called the potential of the electrically charged field in the selected region.

A particle having a charge in an electrically saturated field is affected by the strength of this electrically charged field. This force creates energy for the movement of a charged particle in the field itself. Big charge has big potential.

Video

Any charge that is in an electric field is affected by a force. In this regard, when the charge moves in the field, a certain work of the electric field occurs. How to calculate this work?

The work of an electric field is to transfer electric charges along a conductor. It will be equal to the product of the voltage and the time spent on work.

By applying the formula of Ohm's law, we can get several different versions of the formula for calculating the work of the current:

A = U˖I˖t = I²R˖t = (U²/R)˖t.

In accordance with the law of conservation of energy, the work of the electric field is equal to the change in the energy of a single section of the circuit, and therefore the energy released by the conductor will be equal to the work of the current.

We express in the SI system:

[A] = V˖A˖s = W˖s = J

1 kWh = 3600000 J.

Let's do an experiment. Consider the movement of a charge in the same field, which is formed by two parallel plates A and B and charged opposite charges. In such a field lines of force are perpendicular to these plates throughout their length, and when plate A is positively charged, then E will be directed from A to B.

Suppose that a positive charge q has moved from point a to point b along an arbitrary path ab = s.

Since the force that acts on the charge that is in the field will be equal to F \u003d qE, the work done when the charge moves in the field according to a given path will be determined by the equality:

A = Fs cos α, or A = qFs cos α.

But s cos α = d, where d is the distance between the plates.

It follows from here: A = qEd.

Let's say now the charge q will move from a and b to essentially acb. The work of the electric field done on this path is equal to the sum of the work done on its individual sections: ac = s₁, cb = s₂, i.e.

A = qEs₁ cos α₁ + qEs₂ cos α₂,

A = qE(s₁ cos α₁ + s₂ cos α₂,).

But s₁ cos α₁ + s₂ cos α₂ = d, and hence in this case A = qEd.

In addition, suppose that the charge q moves from a to b along an arbitrary curved line. To calculate the work done on a given curvilinear path, it is necessary to stratify the field between plates A and B with a certain number of which will be so close to each other that individual sections of the path s between these planes can be considered straight.

In this case, the work of the electric field produced on each of these segments of the path will be equal to A₁ = qEd₁, where d₁ is the distance between two adjacent planes. And the total work on the whole path d will be equal to the product of qE and the sum of distances d₁ equal to d. Thus, and as a result curved path the work done will be equal to A = qEd.

The examples we have considered show that the work of an electric field in moving a charge from one point to another does not depend on the shape of the path of movement, but depends solely on the position of these points in the field.

In addition, we know that the work done by gravity when moving a body along an inclined plane of length l will be equal to the work done by the body when falling from a height h, and the height of the inclined plane. This means that the work, or, in particular, the work during the movement of the body in the field of gravity, also does not depend on the shape of the path, but depends only on the difference in heights of the first and last points of the path.

Thus, it can be proved that important property can have not only a homogeneous, but any electric field. Gravity has a similar property.

The work of an electrostatic field in moving a point charge from one point to another is determined by the linear integral:

A₁₂ = ∫ L₁₂q (Edl),

where L₁₂ is the trajectory of the charge, dl is the infinitesimal displacement along the trajectory. If the contour is closed, then the symbol ∫ is used for the integral; in this case, it is assumed that the direction of traversal of the contour is selected.

The work of electrostatic forces does not depend on the shape of the path, but only on the coordinates of the first and last points of movement. Therefore, the field strengths are conservative, while the field itself is potential. It is worth noting that the work of any one along a closed path will be equal to zero.

One of the basic concepts in electricity is the electrostatic field. Its important property is the work of moving a charge in an electric field, which is created by a distributed charge that does not change in time.

Terms of work

The force in an electrostatic field moves a charge from one place to another. It is completely unaffected by the shape of the trajectory. The definition of force depends only on the position of the points at the beginning and end, as well as on the total amount of charge.

Based on this, we can draw the following conclusion: If the trajectory when moving an electric charge is closed, then all the work of forces in the electrostatic field has a zero value. In this case, the shape of the trajectory does not matter, since the Coulomb forces produce the same work. When the direction in which the electric charge moves is reversed, the force itself also changes its sign. Therefore, a closed trajectory, regardless of its shape, determines the entire work produced by the Coulomb forces, equal to zero.

If several point charges take part in the creation of an electrostatic field at once, then their total work will be the sum of the work performed by the Coulomb fields of these charges. The total work, regardless of the shape of the trajectory, is determined solely by the location of the start and end points.

The concept of potential energy of a charge

Characteristic of the electrostatic field, allows you to determine the potential energy of any charge. In addition, with its help, the work of moving a charge in an electric field is more accurately determined. To obtain this value, it is necessary to select a certain point in space and the potential energy of the charge placed at this point.

A charge placed at any point has a potential energy equal to the work done by the electrostatic field during the movement of the charge from one point to another.

IN physical sense, the potential energy is the value for each of two different points in space. At the same time, the work on moving the charge is independent of the paths of its movement and the selected point. The potential of an electrostatic field at a given spatial point is equal to the work done by electric forces when a unit positive charge is removed from this point into infinite space.

The work of the electric field

For every charge in an electric field, there is a force that can move this charge. Determine the work A of moving a point positive charge q from point O to point n, performed by the forces of the electric field of a negative charge Q. According to Coulomb's law, the force that moves the charge is variable and equal to

Where r is the variable distance between charges.

; This expression can be obtained like this

The value is the potential energy W p of the charge at a given point of the electric field:

The sign (-) shows that when a charge is moved by a field, its potential energy decreases, turning into the work of moving.

The value equal to the potential energy of a single positive charge (q=+1) is called the potential of the electric field.

Then

Thus, the potential difference of two points of the field is equal to the work of the field forces in moving a single positive charge from one point to another.

The potential of an electric field point is equal to the work to move a unit positive charge from a given point to infinity.

Unit of measurement - Volt \u003d J / C

The work of moving a charge in an electric field does not depend on the shape of the path, but depends only on the potential difference between the initial and final points of the path.

A surface at all points of which the potential is the same is called equipotential.

The field strength is its power characteristic, and the potential is its energy characteristic.

The relationship between the field strength and its potential is expressed by the formula

,

The sign (-) is due to the fact that the field strength is directed in the direction of decreasing potential, and in the direction of increasing potential.

5. Use of an electric field in medicine.

franklinization, or "electrostatic shower", is a therapeutic method in which the patient's body or parts of it are exposed to a constant electric field of high voltage.

Constant electric field during the procedure overall impact can reach 50 kV, with local exposure 15-20 kV.

Mechanism of therapeutic action. The franklinization procedure is carried out in such a way that the patient's head or another part of the body becomes, as it were, one of the capacitor plates, while the second is an electrode suspended above the head, or installed above the impact site at a distance of 6-10 cm. Under the influence of high voltage under the tips of the needles fixed on the electrode, air ionization occurs with the formation of air ions, ozone and nitrogen oxides.

Inhalation of ozone and air ions causes a reaction in the vasculature. After a short-term vasospasm, capillaries expand not only in superficial tissues, but also in deep ones. As a result, metabolic and trophic processes are improved, and in the presence of tissue damage, the processes of regeneration and restoration of functions are stimulated.

As a result of improved blood circulation, normalization of metabolic processes and nerve function, there is a decrease in headaches, high blood pressure, increased vascular tone, and a decrease in heart rate.

The use of franklinization is indicated for functional disorders nervous system

Examples of problem solving

1. During the operation of the franklinization apparatus, 500,000 light air ions are formed every second in 1 cm 3 of air. Determine the work of ionization required to create the same amount of air ions in 225 cm 3 of air during the treatment session (15 min). The ionization potential of air molecules is assumed to be 13.54 V; conventionally, air is considered to be a homogeneous gas.

is the ionization potential, A is the work of ionization, N is the number of electrons.

2. When treating with an electrostatic shower, a potential difference of 100 kV is applied to the electrodes of the electric machine. Determine what charge passes between the electrodes during one treatment procedure, if it is known that the electric field forces do the work of 1800J.

From here

Electric dipole in medicine

According to Eithoven's theorem, which is the basis of electrocardiography, the heart is an electrical dipole located in the center equilateral triangle(Eithoven's triangle), the vertices of which can be conventionally considered

located in the right hand, left hand and left foot.

During the cardiac cycle, both the position of the dipole in space and the dipole moment change. Measurement of the potential difference between the vertices of the Eithoven triangle allows you to determine the relationship between the projections of the dipole moment of the heart on the sides of the triangle in the following way:

Knowing the voltages U AB , U BC , U AC it is possible to determine how the dipole is oriented with respect to the sides of the triangle.

In electrocardiography, the potential difference between two points on the body (in this case, between the vertices of Eithoven's triangle) is called the lead.

Registration of potential difference in leads depending on time is called electrocardiogram.

The locus of points of the end of the dipole moment vector during the cardiac cycle is called vector cardiogram.

Lecture #4

contact phenomena

1. Contact potential difference. Volta's laws.

2. Thermoelectricity.

3. Thermocouple, its use in medicine.

4. Potential of rest. Action potential and its distribution.

1. With close contact of dissimilar metals, a potential difference arises between them, depending only on their chemical composition and temperature (Volta's first law).

This potential difference is called contact.

In order to leave the metal and go into the environment, the electron must do work against the forces of attraction to the metal. This work is called the work function of the electron from the metal.

Let us bring into contact two different metals 1 and 2, having the work function A 1 and A 2, respectively, and A 1< A 2 . Очевидно, что свободный электрон, попавший в процессе теплового движения на поверхность раздела металлов, будет втянут во второй металл, так как со стороны этого металла на электрон действует большая сила притяжения (A 2 >A1). Consequently, through the contact of metals, free electrons are “pumped” from the first metal to the second, as a result of which the first metal is charged positively, the second negatively. The resulting potential difference creates an electric field of strength E, which makes it difficult to further "pump" the electrons and will completely stop it when the work of moving the electron due to the contact potential difference becomes equal to the work function difference:

(1)

Let us now bring into contact two metals with A 1 = A 2 having different concentrations of free electrons n 01 >n 02 . Then the predominant transfer of free electrons from the first metal to the second will begin. As a result, the first metal will be positively charged, the second - negatively. There will be a potential difference between the metals, which will stop the further transfer of electrons. The resulting potential difference is determined by the expression:

, (2)

where k is Boltzmann's constant

In the general case of the contact of metals that differ both in the work function and in the concentration of free electrons, the c.r.p. from (1) and (2) will be equal to

(3)

It is easy to show that the sum of the contact potential differences of series-connected conductors is equal to the contact potential difference created by the end conductors and does not depend on the intermediate conductors.

This position is called the second law of Volta.

If we now directly connect the end conductors, then the potential difference existing between them is compensated by an equal potential difference arising in contact 1 and 4. Therefore, the K.R.P. does not create current in a closed circuit of metal conductors having the same temperature.

2. Thermoelectricity is the dependence of the contact potential difference on temperature.

Let's make a closed circuit of two dissimilar metal conductors 1 and 2. Temperatures of contacts a and b will be maintained by different T a > T b . Then, according to formula (3), the f.r.p. hot junction more than cold junction:

As a result, a potential difference arises between junctions a and b

It is called thermoelectromotive force, and current I will flow in a closed circuit. Using formula (3), we obtain

Where for each pair of metals

3. A closed circuit of conductors that creates a current due to the difference in temperature of the contacts between the conductors is called thermocouple.

From formula (4) it follows that the thermoelectromotive force of a thermocouple is proportional to the temperature difference of the junctions (contacts).

Formula (4) is also valid for temperatures on the Celsius scale:

A thermocouple can only measure temperature differences. Typically one junction is maintained at 0°C. It's called cold junction. The other junction is called the hot or measurement junction.

The thermocouple has significant advantages over mercury thermometers: it is sensitive, inertialess, allows measuring the temperature of small objects, and allows remote measurements.

Measurement of the limit of the temperature field of the human body.

It is believed that the temperature of the human body is constant, but this constancy is relative, since in different parts of the body the temperature is not the same and varies depending on the functional state of the organism.

Skin temperature has its own well-defined topography. most low temperature(23-30º) have distal limbs, nose tip, auricles. The highest temperature is in the armpit, in the perineum, neck, lips, cheeks. The remaining areas have a temperature of 31-33.5ºС.

In a healthy person, the temperature distribution is symmetrical with respect to middle line body. The violation of this symmetry serves as the main criterion for diagnosing diseases by constructing a temperature field profile using contact devices: a thermocouple and a resistance thermometer.

4 . The surface membrane of a cell is not equally permeable to different ions. In addition, the concentration of any specific ions is different on different sides of the membrane, the most favorable composition of ions is maintained inside the cell. These factors lead to the appearance in a normally functioning cell of a potential difference between the cytoplasm and the environment (resting potential)

When excited, the potential difference between the cell and the environment changes, an action potential arises, which propagates in the nerve fibers.

The mechanism of propagation of an action potential along a nerve fiber is considered by analogy with the propagation of an electromagnetic wave along a two-wire line. However, along with this analogy, there are fundamental differences.

An electromagnetic wave, propagating in a medium, weakens, since its energy is dissipated, turning into the energy of molecular thermal motion. The energy source of an electromagnetic wave is its source: generator, spark, etc.

The excitation wave does not die out, since it receives energy from the very medium in which it propagates (the energy of a charged membrane).

Thus, the propagation of the action potential along the nerve fiber occurs in the form of an autowave. Excitable cells are the active medium.

Examples of problem solving

1. When constructing a profile of the temperature field of the surface of the human body, a thermocouple with a resistance of r 1 = 4 Ohm and a galvanometer with a resistance of r 2 = 80 Ohm are used; I=26mkA at junction temperature difference ºС. What is the thermocouple constant?

The thermopower that occurs in a thermocouple is equal to

(1) where thermocouples, - temperature difference of junctions.

According to Ohm's law for the chain section where U is taken as . Then

Lecture #5

Electromagnetism

1. The nature of magnetism.

2. Magnetic interaction of currents in vacuum. Ampere's law.

4. Dia-, para- and ferromagnetic substances. Magnetic permeability and magnetic induction.

5. Magnetic properties of body tissues.

1 . A magnetic field arises around moving electric charges (currents), through which these charges interact with magnetic or other moving electric charges.

The magnetic field is a force field, it is depicted by means of magnetic lines of force. Unlike the lines of force of the electric field, magnetic lines of force are always closed.

The magnetic properties of a substance are due to elementary circular currents in the atoms and molecules of this substance.

2 . Magnetic interaction of currents in vacuum. Ampère's law.

The magnetic interaction of currents was studied using movable wire circuits. Ampere found that the magnitude of the force of interaction of two small sections of conductors 1 and 2 with currents is proportional to the lengths of these sections, the currents I 1 and I 2 in them and is inversely proportional to the square of the distance r between the sections:

It turned out that the force of the impact of the first section on the second depends on their relative position and is proportional to the sines of the angles and .