Among physical quantities, an important place is occupied by magnetic flux. This article explains what it is and how to determine its size.
Formula-magnitnogo-potoka-600x380.jpg?x15027" alt="Magnetic flux formula" width="600" height="380">!}
Magnetic flux formula
What is magnetic flux
This is the quantity that determines the level magnetic field passing through the surface. It is designated “FF” and depends on the strength of the field and the angle of passage of the field through this surface.
It is calculated according to the formula:
FF=B⋅S⋅cosα, where:
- FF – magnetic flux;
- B is the magnitude of magnetic induction;
- S is the surface area through which this field passes;
- cosα is the cosine of the angle between the perpendicular to the surface and the flow.
The SI unit of measurement is “weber” (Wb). 1 Weber is created by a field of 1 Tesla passing perpendicular to a surface with an area of 1 m².
Thus, the flow is maximum when its direction coincides with the vertical and is equal to “0” if it is parallel to the surface.
Interesting. The magnetic flux formula is similar to the formula by which illumination is calculated.
Permanent magnets
One of the field sources is permanent magnets. They have been known for many centuries. The compass needle was made from magnetized iron, and in Ancient Greece There was a legend about an island that attracts metal parts of ships.
There are permanent magnets various shapes and are made from different materials:
- iron ones are the cheapest, but have less attractive force;
- neodymium - made from an alloy of neodymium, iron and boron;
- Alnico is an alloy of iron, aluminum, nickel and cobalt.
All magnets are bipolar. This is most noticeable in rod and horseshoe devices.
If the rod is suspended from the middle or placed on a floating piece of wood or foam, it will turn in the north-south direction. The pole pointing north is called the north pole and is painted in color on laboratory instruments. Blue colour and denoted by "N". The opposite one, pointing south, is red and labeled "S". Magnets with like poles attract, and with opposite poles they repel.
In 1851, Michael Faraday proposed the concept of closed induction lines. These lines come out of the north pole of the magnet, pass through the surrounding space, enter the south and return to the north inside the device. The lines and field strength are closest at the poles. The attractive force is also higher here.
If you put a piece of glass on the device and sprinkle iron filings on top in a thin layer, they will be located along the magnetic field lines. When several devices are placed nearby, the sawdust will show the interaction between them: attraction or repulsion.
Magnit-i-zheleznye-opilki-600x425.jpeg?x15027" alt="Magnet and iron filings" width="600" height="425">!}
Magnet and iron filings
Earth's magnetic field
Our planet can be imagined as a magnet, the axis of which is inclined by 12 degrees. The intersections of this axis with the surface are called magnetic poles. Like any magnet, power lines The lands go from the north pole to the south. Near the poles they run perpendicular to the surface, so there the compass needle is unreliable, and other methods have to be used.
Particles " solar wind» have electric charge, therefore, when moving around them, a magnetic field appears, interacting with the Earth’s field and directing these particles along the lines of force. Thus, this field protects earth's surface from cosmic radiation. However, near the poles, these lines are directed perpendicular to the surface, and charged particles enter the atmosphere, causing the northern lights.
Electromagnets
In 1820, Hans Oersted, while conducting experiments, saw the effect of a conductor through which an electric current flows on a compass needle. A few days later, Andre-Marie Ampere discovered the mutual attraction of two wires through which a current flowed in the same direction.
Interesting. During electric welding, nearby cables move when the current changes.
Ampere later suggested that this was due to the magnetic induction of current flowing through the wires.
In a coil wound with an insulated wire through which electric current flows, the fields of the individual conductors reinforce each other. To increase the attractive force, the coil is wound on an open steel core. This core is magnetized and attracts iron parts or the other half of the core in relays and contactors.
Elektromagnit-1-600x424.jpg?x15027" alt="Electromagnets" width="600" height="424">!}
Electromagnets
Electromagnetic induction
When the magnetic flux changes, an electric current is induced in the wire. This fact does not depend on what causes this change: the movement of a permanent magnet, the movement of a wire, or a change in the current strength in a nearby conductor.
This phenomenon was discovered by Michael Faraday on August 29, 1831. His experiments showed that the EMF (electromotive force) appearing in a circuit bounded by conductors is directly proportional to the rate of change of flux passing through the area of this circuit.
Important! For an emf to occur, the wire must cross the power lines. When moving along the lines, there is no EMF.
If the coil in which the emf occurs is switched on electrical circuit, then a current arises in the winding, creating its own electromagnetic field in the inductor.
Right hand rule
When a conductor moves in a magnetic field, an emf is induced in it. Its direction depends on the direction of movement of the wire. The method by which the direction of magnetic induction is determined is called the “method right hand».
Pravilo-pravoj-ruki-600x450.jpg?x15027" alt="Right hand rule" width="600" height="450">!}
Right hand rule
Calculating the magnitude of the magnetic field is important for the design of electrical machines and transformers.
Video
If an electric current, as Oersted's experiments showed, creates a magnetic field, then couldn't the magnetic field in turn cause an electric current in a conductor? Many scientists tried to find the answer to this question with the help of experiments, but Michael Faraday (1791 - 1867) was the first to solve this problem.
In 1831, Faraday discovered that an electric current arises in a closed conducting circuit when the magnetic field changes. This current was called induction current.
An induction current in a coil of metal wire occurs when a magnet is pushed into the coil and when a magnet is pulled out of the coil (Fig. 192),
and also when the current strength changes in the second coil, the magnetic field of which penetrates the first coil (Fig. 193).
Emergence phenomenon electric current in a closed conducting loop with changes in the magnetic field penetrating the loop is called electromagnetic induction.
The appearance of an electric current in a closed circuit with changes in the magnetic field penetrating the circuit indicates the action of external forces of a non-electrostatic nature in the circuit or the occurrence of Induction emf. A quantitative description of the phenomenon of electromagnetic induction is given on the basis of establishing a connection between the induced emf and a physical quantity called magnetic flux.
Magnetic flux. For a flat circuit located in a uniform magnetic field (Fig. 194), the magnetic flux F through a surface area S called a quantity equal to the product of the magnitude of the magnetic induction vector and the area S and the cosine of the angle between the vector and the normal to the surface:
Lenz's rule. Experience shows that the direction of the induced current in the circuit depends on whether the magnetic flux passing through the circuit increases or decreases, as well as on the direction of the magnetic field induction vector relative to the circuit. General rule, which makes it possible to determine the direction of the induction current in the circuit, was established in 1833 by E. X. Lenz.
Lenz's rule can be clearly demonstrated using a lightweight aluminum ring (Fig. 195).
Experience shows that when a permanent magnet is introduced, the ring is repelled from it, and when removed, it is attracted to the magnet. The result of the experiments does not depend on the polarity of the magnet.
The repulsion and attraction of a solid ring is explained by the occurrence of an induction current in the ring when the magnetic flux through the ring changes and the effect of a magnetic field on the induction current. It is obvious that when a magnet is pushed into the ring, the induction current in it has such a direction that the magnetic field created by this current counteracts the external magnetic field, and when the magnet is pulled out, the induction current in it has such a direction that the induction vector of its magnetic field coincides in direction with the vector external field induction.
General wording Lenz's rules: the induced current arising in a closed circuit has such a direction that the magnetic flux created by it through the area limited by the circuit tends to compensate for the change in the magnetic flux that causes this current.
Law of electromagnetic induction. An experimental study of the dependence of induced emf on changes in magnetic flux led to the establishment law of electromagnetic induction: The induced emf in a closed loop is proportional to the rate of change of the magnetic flux through the surface bounded by the loop.
In the SI, the unit of magnetic flux is chosen such that the proportionality coefficient between the induced emf and the change in magnetic flux is equal to unity. Wherein law of electromagnetic induction is formulated as follows: the induced emf in a closed loop is equal to the modulus of the rate of change of the magnetic flux through the surface limited by the loop:
Taking into account Lenz's rule, the law of electromagnetic induction is written as follows:
Induction emf in a coil. If identical changes in magnetic flux occur in series-connected circuits, then the induced emf in them is equal to the sum of the induced emf in each of the circuits. Therefore, when the magnetic flux changes in a coil consisting of n identical turns of wire, the total induced emf in n times the induced emf in a single circuit:
For a uniform magnetic field, based on equation (54.1), it follows that its magnetic induction is equal to 1 T, if the magnetic flux through a circuit with an area of \u200b\u200b1 m 2 is equal to 1 Wb:
.
Vortex electric field. The law of electromagnetic induction (54.3) from the known rate of change of magnetic flux allows us to find the value of the induced emf in the circuit and at known meaning electrical resistance circuit, calculate the current in the circuit. However, the physical meaning of the phenomenon of electromagnetic induction remains undisclosed. Let's consider this phenomenon in more detail.
The occurrence of an electric current in a closed circuit indicates that when the magnetic flux penetrating the circuit changes, forces act on the free electric charges in the circuit. The circuit wire is motionless; the free electric charges in it can be considered motionless. Stationary electric charges can only be affected by an electric field. Consequently, with any change in the magnetic field in the surrounding space, an electric field appears. This electric field sets in motion free electric charges in the circuit, creating an inductive electric current. The electric field that arises when the magnetic field changes is called vortex electric field.
The work of the forces of the vortex electric field to move electric charges is the work of external forces, the source of induced emf.
The vortex electric field differs from the electrostatic field in that it is not associated with electric charges; its tension lines are closed lines. The work done by the forces of a vortex electric field when an electric charge moves along a closed line can be different from zero.
Induction emf in moving conductors. The phenomenon of electromagnetic induction is also observed in cases where the magnetic field does not change over time, but the magnetic flux through the circuit changes due to the movement of the circuit conductors in the magnetic field. In this case, the cause of the induced emf is not the vortex electric field, but the Lorentz force.
Let there be a magnetic field in some small region of space that can be considered uniform, that is, in this region the magnetic induction vector is constant, both in magnitude and direction.
Let us select a small area with an area ΔS, the orientation of which is specified by the unit normal vector n(Fig. 445).
rice. 445
Magnetic flux through this area ΔФ m is defined as the product of the area of the site and the normal component of the magnetic field induction vector
Where 
dot product of vectors B And n;
Bn− component of the magnetic induction vector normal to the site.
In an arbitrary magnetic field, the magnetic flux through an arbitrary surface is determined as follows (Fig. 446): 
rice. 446
− the surface is divided into small areas ΔSi(which can be considered flat);
− the induction vector is determined B i on this site (which within the site can be considered permanent);
− the sum of flows through all areas into which the surface is divided is calculated
This amount is called flux of the magnetic field induction vector through a given surface (or magnetic flux).
Note that when calculating the flux, the summation is carried out over the field observation points, and not over the sources, as when using the superposition principle. Therefore, magnetic flux is an integral characteristic of the field, describing its averaged properties over the entire surface under consideration.
It is difficult to find the physical meaning of magnetic flux, as for other fields it is a useful auxiliary physical quantity. But unlike other fluxes, magnetic flux is so common in applications that in the SI system it was awarded a “personal” unit of measurement - Weber 2: 1 Weber− magnetic flux of a uniform magnetic field of induction 1 T across the area 1 m2 oriented perpendicular to the magnetic induction vector.
Now we will prove a simple but extremely important theorem about magnetic flux through a closed surface.
Previously, we established that the forces of any magnetic field are closed; it already follows from this that the magnetic flux through any closed surface is equal to zero.
Nevertheless, we present a more formal proof of this theorem.
First of all, we note that the principle of superposition is valid for magnetic flux: if a magnetic field is created by several sources, then for any surface the flux of the field created by a system of current elements equal to the sum flows of fields created by each current element separately.
This statement follows directly from the superposition principle for the induction vector and the directly proportional relationship between the magnetic flux and the magnetic induction vector. Therefore, it is sufficient to prove the theorem for the field created by a current element, the induction of which is determined by the Biot-Savarre-Laplace law. Here the structure of the field, which has axial circular symmetry, is important for us; the value of the modulus of the induction vector is unimportant. 
Let us choose as a closed surface the surface of a block cut out as shown in Fig. 447.
rice. 447 The magnetic flux is non-zero only through its two side faces
, but these flows have opposite signs. Recall that for a closed surface, an outer normal is chosen, so on one of the indicated faces (the front) the flux is positive, and on the back it is negative. Moreover, the modules of these flows are equal, since the distribution of the field induction vector on these faces is the same. This result does not depend on the position of the considered block. An arbitrary body can be divided into infinitesimal parts, each of which is similar to the considered bar. 
Finally, let us formulate another important property of the flow of any vector field. Let an arbitrary closed surface bound a certain body (Fig. 448).
rice. 448 Let us divide this body into two parts, limited by parts of the original surface And Ω 1, and close them with a common interface between the body. The sum of the fluxes through these two closed surfaces is equal to the flux through the original surface! Indeed, the sum of the flows across the boundary (once for one body, another time for another) is equal to zero, since in each case it is necessary to take different, opposite normals (each time external). Similarly, one can prove the statement for an arbitrary partition of a body: if a body is divided into an arbitrary number of parts, then the flux through the surface of the body is equal to the sum of the fluxes through the surfaces of all parts of the partition of the body. This statement is obvious for fluid flow.
In fact, we have proven that if the flux of a vector field is zero through some surface bounding a small volume, then this flux is zero through any closed surface.
So, for any magnetic field the magnetic flux theorem is valid: the magnetic flux through any closed surface is zero Ф m = 0.
Previously, we looked at flow theorems for the fluid velocity field and the electrostatic field. In these cases, the flow through a closed surface was completely determined by point sources of the field (sources and sinks of liquid, point charges). IN general case the presence of a non-zero flux through a closed surface indicates the presence of point field sources. Hence, The physical content of the magnetic flux theorem is the statement about the absence of magnetic charges.
If you have a good understanding of this issue and are able to explain and defend your point of view, then you can formulate the magnetic flux theorem like this: “No one has yet found the Dirac monopole.”
It should be especially emphasized that when we talk about the absence of field sources, we mean precisely point sources, similar to electric charges. If we draw an analogy with the field of a moving fluid, electric charges are like points from which fluid flows out (or flows in), increasing or decreasing its amount. The emergence of a magnetic field, due to the movement of electric charges, is similar to the movement of a body in a liquid, which leads to the appearance of vortices that do not change total number liquids.
Vector fields for which the flux through any closed surface is equal to zero have received a beautiful, exotic name − solenoidal. A solenoid is a coil of wire through which electric current can be passed. Such a coil can create strong magnetic fields, so the term solenoidal means “similar to the field of a solenoid,” although such fields could be called more simply “magnetic-like.” Finally, such fields are also called vortex, similar to the velocity field of a fluid that forms all kinds of turbulent vortices in its movement.
The magnetic flux theorem has great importance, it is often used to prove various properties of magnetic interactions, and we will encounter it more than once. For example, the magnetic flux theorem proves that the induction vector of the magnetic field created by an element cannot have a radial component, otherwise the flux through a cylindrical surface coaxial with the current element would be non-zero.
We now illustrate the application of the magnetic flux theorem to calculate the magnetic field induction. Let the magnetic field be created by a ring with current, which is characterized by a magnetic moment p m. Let us consider the field near the axis of the ring at a distance z from the center, significantly larger than the radius of the ring (Fig. 449). 
rice. 449
Previously, we obtained a formula for the magnetic field induction on the axis for large distances from the center of the ring 
We will not make a big mistake if we assume that the vertical (let the axis of the ring is vertical) component of the field within a small ring of radius has the same value r, the plane of which is perpendicular to the axis of the ring. Since the vertical field component changes with distance, radial field components must inevitably be present, otherwise the magnetic flux theorem will not hold! It turns out that this theorem and formula (3) are enough to find this radial component. Select a thin cylinder with a thickness Δz and radius r, the lower base of which is at a distance z from the center of the ring, coaxial with the ring and apply the magnetic flux theorem to the surface of this cylinder. The magnetic flux through the lower base is equal to (note that the induction and normal vectors are opposite here) 
Where Bz(z) z;
the flow through the upper base is
Where B z (z + Δz)− value of the vertical component of the induction vector at height z + Δz;
flow through the side surface (from axial symmetry it follows that the modulus of the radial component of the induction vector B r is constant on this surface): 
According to the proven theorem, the sum of these flows is equal to zero, so the equation is valid
from which we determine the required value
It remains to use formula (3) for the vertical component of the field and carry out the necessary calculations 3 
Indeed, a decrease in the vertical component of the field leads to the appearance of horizontal components: a decrease in outflow through the bases leads to “leakage” through the side surface.
Thus, we have proven the “criminal theorem”: if less flows out of one end of a pipe than is poured into it from the other end, then somewhere they are stealing through the side surface.
1 It is enough to take the text with the definition of the flow of the electric field strength vector and change the notation (which is what is done here).
2 Named in honor of the German physicist (member of the St. Petersburg Academy of Sciences) Wilhelm Eduard Weber (1804 - 1891)
3 The most literate can see the derivative of function (3) in the last fraction and simply calculate it, but we have to Once again use the approximate formula (1 + x) β ≈ 1 + βx.
Right hand or gimlet rule:
The direction of the magnetic field lines and the direction of the current creating it are interconnected by the well-known rule of the right hand or gimlet, which was introduced by D. Maxwell and is illustrated by the following drawings:
Few people know that a gimlet is a tool for drilling holes in wood. Therefore, it is more understandable to call this rule the rule of a screw, screw or corkscrew. However, grabbing the wire as in the picture is sometimes life-threatening!
Magnetic induction B:
Magnetic induction- is the main fundamental characteristic of the magnetic field, similar to the electric field strength vector E. The magnetic induction vector is always directed tangentially to the magnetic line and shows its direction and strength. The unit of magnetic induction in B = 1 T is taken to be the magnetic induction of a uniform field, in which a section of conductor with a length of l= 1 m, with a current strength in it in I= 1 A, acts from the side of the field maximum force Ampere - F= 1 H. The direction of the Ampere force is determined by the left hand rule. In the CGS system, magnetic field induction is measured in gauss (G), in the SI system - in tesla (T).
Magnetic field strength H:
Another characteristic of the magnetic field is tension, which is an analogue of the electric displacement vector D in electrostatics. Determined by the formula:
Magnetic field strength is a vector quantity and is quantitative characteristics magnetic field and does not depend on magnetic properties environment. In the CGS system, magnetic field strength is measured in oersteds (Oe), in the SI system - in amperes per meter (A/m).
Magnetic flux F:
Magnetic flux Ф is a scalar physical quantity that characterizes the number of magnetic induction lines penetrating a closed circuit. 
Let's consider a special case. IN uniform magnetic field, the magnitude of the induction vector of which is equal to ∣B ∣, is placed flat closed loop area S. The normal n to the contour plane makes an angle α with the direction of the magnetic induction vector B. The magnetic flux through the surface is the quantity Ф, determined by the relation:
In general, magnetic flux is defined as the integral of the magnetic induction vector B through a finite surface S.
It is worth noting that the magnetic flux through any closed surface is zero (Gauss's theorem for magnetic fields). This means that the magnetic field lines do not break off anywhere, i.e. the magnetic field has a vortex nature, and also that it is impossible for the existence of magnetic charges that would create a magnetic field in the same way that electric charges create an electric field. In the SI, the unit of magnetic flux is Weber (Wb), in the CGS system it is Maxwell (Mx); 1 Wb = 10 8 μs.
Definition of inductance:
Inductance is a coefficient of proportionality between the electric current flowing in any closed circuit and the magnetic flux created by this current through the surface of which this circuit is the edge.
Otherwise, inductance is a proportionality coefficient in the self-induction formula.
In SI units, inductance is measured in henry (H). A circuit has an inductance of one henry if, when the current changes by one ampere per second, a self-inductive emf of one volt appears at the circuit terminals.
The term “inductance” was coined by Oliver Heaviside, a self-taught English scientist, in 1886. Simply put, inductance is the property of a current-carrying conductor to accumulate energy in a magnetic field, equivalent to capacitance for an electric field. It does not depend on the magnitude of the current, but only on the shape and size of the conductor carrying the current. To increase the inductance, the conductor is wound in coils, the calculation of which is what the program is dedicated to
A MAGNETIC FIELD
The magnetic interaction of moving electric charges, according to the concepts of field theory, is explained as follows: every moving electric charge creates a magnetic field in the surrounding space that can act on other moving electric charges.
B is a physical quantity that is a force characteristic of a magnetic field. It is called magnetic induction (or magnetic field induction).
Magnetic induction- vector quantity. The magnitude of the magnetic induction vector is equal to the ratio maximum value Ampere force acting on a straight conductor with current, to the current strength in the conductor and its length:
Unit of magnetic induction. IN International system units per unit of magnetic induction is the induction of such a magnetic field in which for each meter of conductor length at a current strength of 1 A a maximum Ampere force of 1 N acts. This unit is called tesla (abbreviated: T), in honor of the outstanding Yugoslav physicist N. Tesla:
LORENTZ FORCE
The movement of a current-carrying conductor in a magnetic field shows that the magnetic field acts on moving electric charges. Ampere force acts on the conductor F A = IBlsin a, and the Lorentz force acts on a moving charge:
Where a- angle between vectors B and v.
Movement of charged particles in a magnetic field. In a uniform magnetic field, a charged particle moving at a speed perpendicular to the magnetic field induction lines is acted upon by a force m, constant in magnitude and directed perpendicular to the velocity vector. Under the influence of a magnetic force, the particle acquires acceleration, the modulus of which is equal to:
In a uniform magnetic field, this particle moves in a circle. The radius of curvature of the trajectory along which the particle moves is determined from the condition from which it follows,
The radius of curvature of the trajectory is a constant value, since a force perpendicular to the velocity vector changes only its direction, but not its magnitude. And this means that this trajectory is a circle.
The period of revolution of a particle in a uniform magnetic field is equal to:
The last expression shows that the period of revolution of a particle in a uniform magnetic field does not depend on the speed and radius of its trajectory.
If the electric field strength is zero, then the Lorentz force l is equal to the magnetic force m:
ELECTROMAGNETIC INDUCTION
The phenomenon of electromagnetic induction was discovered by Faraday, who established that an electric current arises in a closed conducting circuit with any change in the magnetic field penetrating the circuit.
MAGNETIC FLUX
Magnetic flux F(flux of magnetic induction) through a surface of area S- a value equal to the product of the magnitude of the magnetic induction vector and the area S and cosine of the angle A between the vector and the normal to the surface:
Ф=BScos
In SI, the unit of magnetic flux is 1 Weber (Wb) - magnetic flux through a surface of 1 m2 located perpendicular to the direction of a uniform magnetic field, the induction of which is 1 T:
Electromagnetic induction- the phenomenon of the occurrence of electric current in a closed conducting circuit with any change in the magnetic flux penetrating the circuit.
Arising in a closed loop, the induced current has such a direction that its magnetic field counteracts the change in the magnetic flux that causes it (Lenz's rule).
LAW OF ELECTROMAGNETIC INDUCTION
Faraday's experiments showed that the strength of the induced current I i in a conducting circuit is directly proportional to the rate of change in the number of magnetic induction lines penetrating the surface bounded by this circuit.
Therefore, the strength of the induction current is proportional to the rate of change of the magnetic flux through the surface bounded by the contour:
It is known that if a current appears in the circuit, this means that external forces act on the free charges of the conductor. The work done by these forces to move a unit charge along a closed loop is called electromotive force (EMF). Let's find the induced emf ε i.
According to Ohm's law for a closed circuit
Since R does not depend on , then
The induced emf coincides in direction with the induced current, and this current, in accordance with Lenz’s rule, is directed so that the magnetic flux it creates counteracts the change in the external magnetic flux.
Law of Electromagnetic Induction
The induced emf in a closed loop is equal to the rate of change of the magnetic flux passing through the loop taken with the opposite sign:
SELF-INDUCTION. INDUCTANCE
Experience shows that magnetic flux F associated with a circuit is directly proportional to the current in that circuit:
Ф = L*I .
Loop inductance L- proportionality coefficient between the current passing through the circuit and the magnetic flux created by it.
The inductance of a conductor depends on its shape, size and properties of the environment.
Self-induction- the phenomenon of the occurrence of induced emf in a circuit when the magnetic flux changes caused by a change in the current passing through the circuit itself.
Self-induction is a special case of electromagnetic induction.
Inductance is a quantity numerically equal to the self-inductive emf that occurs in a circuit when the current in it changes by one per unit of time.
In SI, the unit of inductance is taken to be the inductance of a conductor in which, when the current strength changes by 1 A in 1 s, a self-inductive emf of 1 V occurs. This unit is called henry (H):
The phenomenon of self-induction is similar to the phenomenon of inertia. Inductance plays the same role when changing current as mass does when changing the speed of a body. The analogue of speed is current.
This means that the energy of the magnetic field of the current can be considered a value similar to kinetic energy body:
Let us assume that after disconnecting the coil from the source, the current in the circuit decreases with time according to a linear law.
The self-induced emf in this case has a constant value:
where I - initial value current, t is the period of time during which the current decreases from I to 0.
During time t, an electric charge passes through the circuit q = I cp t. Because I cp = (I + 0)/2 = I/2, then q=It/2. Therefore, the work of electric current:
This work is done due to the energy of the magnetic field of the coil. Thus we again get:
Example. Determine the energy of the magnetic field of the coil in which, at a current of 7.5 A, the magnetic flux is 2.3 * 10 -3 Wb. How will the field energy change if the current strength is halved?
The energy of the magnetic field of the coil is W 1 = LI 1 2 /2. By definition, the inductance of the coil is L = Ф/I 1. Hence,
Loading...
