ABSTRACT
In the subject "Physics"
Topic: “Application of the Lorentz force”
Completed by: Student of group T-10915 Logunova M.V.
Teacher Vorontsov B.S.
Kurgan 2016
Introduction. 3
1. Use of the Lorentz force. 4
.. 4
1. 2 Mass spectrometry. 6
1. 3 MHD generator. 7
1. 4 Cyclotron. 8
Conclusion. eleven
List of used literature... 13
Introduction
Lorentz force- the force with which the electromagnetic field, according to classical (non-quantum) electrodynamics, acts on a point charged particle. Sometimes the Lorentz force is called the force acting on a moving object with speed υ charge q only from the outside magnetic field, often with full force - from the side electromagnetic field in general, in other words, from the electrical side E and magnetic B fields.
In the International System of Units (SI) it is expressed as:
F L = q υ B sin α
It is named after the Dutch physicist Hendrik Lorentz, who derived an expression for this force in 1892. Three years before Lorenz, the correct expression was found by O. Heaviside.
The macroscopic manifestation of the Lorentz force is the Ampere force.
Using the Lorentz force
The effect exerted by a magnetic field on moving charged particles is very widely used in technology.
The main application of the Lorentz force (more precisely, its special case - the Ampere force) is electric cars(electric motors and generators). The Lorentz force is widely used in electronic devices to influence charged particles (electrons and sometimes ions), for example, in television cathode ray tubes , V mass spectrometry And MHD generators.
Also, in the currently created experimental installations for carrying out a controlled thermonuclear reaction, the action of a magnetic field on the plasma is used to twist it into a cord that does not touch the walls of the working chamber. The circular motion of charged particles in a uniform magnetic field and the independence of the period of such motion from the particle speed are used in cyclic accelerators of charged particles - cyclotrons.
1. 1. Electron beam devices
Electron beam devices (EBDs) are a class of vacuum electronic devices that use a flow of electrons, concentrated in the form of a single beam or beam of beams, which are controlled both in intensity (current) and position in space, and interact with a stationary spatial target (screen) of the device. The main scope of application of ELP is the conversion of optical information into electrical signals and inverse conversion electrical signal into an optical signal - for example, into a visible television image.
The class of cathode-ray devices does not include X-ray tubes, photocells, photomultipliers, gas-discharge devices (dekatrons) and receiving and amplifying electron tubes (beam tetrodes, electric vacuum indicators, lamps with secondary emission, etc.) with a beam form of currents.
An electron beam device consists of at least three main parts:
· An electronic spotlight (gun) forms an electron beam (or a beam of rays, for example, three beams in a color picture tube) and controls its intensity (current);
· The deflection system controls the spatial position of the beam (its deviation from the axis of the spotlight);
· The target (screen) of the receiving ELP converts the energy of the beam into the luminous flux of a visible image; the target of the transmitting or storing ELP accumulates a spatial potential relief, read by a scanning electron beam
| Rice. 1 CRT device |
General principles devices.
A deep vacuum is created in the CRT cylinder. To create an electron beam, a device called an electron gun is used. The cathode, heated by the filament, emits electrons. By changing the voltage on the control electrode (modulator), you can change the intensity of the electron beam and, accordingly, the brightness of the image. After leaving the gun, the electrons are accelerated by the anode. Next, the beam passes through a deflection system, which can change the direction of the beam. Television CRTs use a magnetic deflection system as it provides large deflection angles. Oscillographic CRTs use an electrostatic deflection system as it provides greater performance. The electron beam hits a screen covered with phosphor. Bombarded by electrons, the phosphor glows and a rapidly moving spot of variable brightness creates an image on the screen.
1. 2 Mass spectrometry
| Rice. 2 |
The Lorentz force is also used in instruments called mass spectrographs, which are designed to separate charged particles according to their specific charges.
Mass spectrometry(mass spectroscopy, mass spectrography, mass spectral analysis, mass spectrometric analysis) - a method for studying a substance based on determining the mass-to-charge ratio of ions formed by ionization of the sample components of interest. One of the most powerful ways of qualitative identification of substances, which also allows quantitative determination. We can say that mass spectrometry is the “weighing” of the molecules in a sample.
The diagram of the simplest mass spectrograph is shown in Figure 2.
In chamber 1, from which the air has been evacuated, there is an ion source 3. The chamber is placed in a uniform magnetic field, at each point of which the induction B⃗ B→ is perpendicular to the plane of the drawing and directed towards us (in Figure 1 this field is indicated by circles). An accelerating voltage is applied between electrodes A and B, under the influence of which the ions emitted from the source are accelerated and at a certain speed enter the magnetic field perpendicular to the induction lines. Moving in a magnetic field along a circular arc, the ions fall on photographic plate 2, which makes it possible to determine the radius R of this arc. Knowing the magnetic field induction B and the speed υ of ions, according to the formula
the specific charge of ions can be determined. And if the charge of the ion is known, its mass can be calculated.
The history of mass spectrometry dates back to the seminal experiments of J. J. Thomson at the beginning of the 20th century. The ending “-metry” in the name of the method appeared after the widespread transition from detecting charged particles using photographic plates to electrical measurements of ion currents.
Mass spectrometry is especially widely used in the analysis of organic substances, since it provides confident identification of both relatively simple and complex molecules. The only thing general requirement- so that the molecule can be ionized. However, by now it has been invented
There are so many ways to ionize sample components that mass spectrometry can be considered an almost all-encompassing method.
1. 3 MHD generator
Magnetohydrodynamic generator, MHD generator is a power plant in which the energy of a working fluid (liquid or gaseous electrically conducting medium) moving in a magnetic field is converted directly into electrical energy.
The operating principle of an MHD generator, like a conventional machine generator, is based on the phenomenon electromagnetic induction, that is, on the occurrence of a current in a conductor crossing the magnetic field lines. Unlike machine generators, the conductor in an MHD generator is the working fluid itself.
The working fluid moves across the magnetic field, and under the influence of the magnetic field, oppositely directed flows of charge carriers of opposite signs arise.
The Lorentz force acts on a charged particle.
The following media can serve as the working fluid of the MHD generator:
· electrolytes;
· liquid metals;
· plasma (ionized gas).
The first MHD generators used electrically conductive liquids (electrolytes) as the working fluid. Currently, plasma is used in which the charge carriers are mainly free electrons and positive ions. Under the influence of a magnetic field, charge carriers deviate from the trajectory along which the gas would move in the absence of the field. In this case, a Hall field can arise in a strong magnetic field (see Hall effect) - electric field, formed as a result of collisions and displacements of charged particles in a plane perpendicular to the magnetic field.
1. 4 Cyclotron
A cyclotron is a resonant cyclic accelerator of non-relativistic heavy charged particles (protons, ions), in which the particles move in a constant and uniform magnetic field, and a high-frequency electric field of constant frequency is used to accelerate them.
The circuit diagram of the cyclotron is shown in Fig. 3. Heavy charged particles (protons, ions) enter the chamber from an injector near the center of the chamber and are accelerated by an alternating field of a fixed frequency applied to the accelerating electrodes (there are two of them and they are called dees). Particles with charge Ze and mass m move in a constant magnetic field of intensity B, directed perpendicular to the plane of motion of the particles, in an unwinding spiral. The radius R of the trajectory of a particle having a speed v is determined by the formula
where γ = -1/2 is the relativistic factor.
In a cyclotron, for a nonrelativistic (γ ≈ 1) particle in a constant and uniform magnetic field, the orbital radius is proportional to the speed (1), and the rotation frequency of the nonrelativistic particle (the cyclotron frequency does not depend on the particle energy
| E = mv 2 /2 = (Ze) 2 B 2 R 2 /(2m) (3) |
In the gap between the dees, particles are accelerated by a pulsed electric field (there is no electric field inside hollow metal dees). As a result, the energy and radius of the orbit increase. By repeating the acceleration by the electric field at each revolution, the energy and radius of the orbit are brought to the maximum acceptable values. In this case, the particles acquire a speed v = ZeBR/m and the corresponding energy:
At the last turn of the spiral, a deflecting electric field is turned on, leading the beam out. The constancy of the magnetic field and the frequency of the accelerating field make continuous acceleration possible. While some particles are moving along the outer turns of the spiral, others are in the middle of the path, and others are just beginning to move.
The disadvantage of the cyclotron is the limitation by essentially non-relativistic energies of particles, since even not very large relativistic corrections (deviations of γ from unity) disrupt the synchronism of acceleration at different turns and particles with significantly increased energies no longer have time to end up in the gap between the dees in the phase of the electric field required for acceleration . In conventional cyclotrons, protons can be accelerated to 20-25 MeV.
To accelerate heavy particles in an unwinding spiral mode to energies tens of times higher (up to 1000 MeV), a modification of the cyclotron called isochronous(relativistic) cyclotron, as well as a phasotron. In isochronous cyclotrons, relativistic effects are compensated by a radial increase in the magnetic field.
Conclusion
Hidden text
Written conclusion (the most basic for all subparagraphs of the first section - principles of action, definitions)
List of used literature
1. Wikipedia [Electronic resource]: Lorentz force. URL: https://ru.wikipedia.org/wiki/Lorentz_Force
2. Wikipedia [Electronic resource]: Magnetohydrodynamic generator. URL: https://ru.wikipedia.org/wiki/ Magnetohydrodynamic_generator
3. Wikipedia [Electronic resource]: Electron beam devices. URL: https://ru.wikipedia.org/wiki/ Electron-beam_devices
4. Wikipedia [Electronic resource]: Mass spectrometry. URL: https://ru.wikipedia.org/wiki/Mass spectrometry
5. Nuclear physics on the Internet [Electronic resource]: Cyclotron. URL: http://nuclphys.sinp.msu.ru/experiment/accelerators/ciclotron.htm
6. Electronic textbook of physics [Electronic resource]: T. Applications of the Lorentz force // URL: http://www.physbook.ru/index.php/ T. Applications of the Lorentz force
7. Academician [Electronic resource]: Magnetohydrodynamic generator // URL: http://dic.academic.ru/dic.nsf/enc_physics/MAGNETOHYDRODYNAMIC
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Along with the Ampere force, Coulomb interaction, and electromagnetic fields, the concept of Lorentz force is often encountered in physics. This phenomenon is one of the fundamental ones in electrical engineering and electronics, along with, and others. It affects charges that move in a magnetic field. In this article we will briefly and clearly examine what the Lorentz force is and where it is applied.
Definition
When electrons move along a conductor, a magnetic field appears around it. At the same time, if you place a conductor in a transverse magnetic field and move it, an electromagnetic induction emf will arise. If a current flows through a conductor located in a magnetic field, the Ampere force acts on it.
Its value depends on the flowing current, the length of the conductor, the magnitude of the magnetic induction vector and the sine of the angle between the magnetic field lines and the conductor. It is calculated using the formula:
The force under consideration is partly similar to that discussed above, but acts not on a conductor, but on a moving charged particle in a magnetic field. The formula looks like:
Important! The Lorentz force (Fl) acts on an electron moving in a magnetic field, and on a conductor - Ampere.
From the two formulas it is clear that in both the first and second cases, the closer the sine of the angle alpha is to 90 degrees, the greater the effect on the conductor or charge by Fa or Fl, respectively.
So, the Lorentz force characterizes not the change in velocity, but the effect of the magnetic field on a charged electron or positive ion. When exposed to them, Fl does not do any work. Accordingly, it is the direction of the charged particle’s velocity that changes, and not its magnitude.
As for the unit of measurement of the Lorentz force, as in the case of other forces in physics, such a quantity as Newton is used. Its components:
How is the Lorentz force directed?
To determine the direction of the Lorentz force, as with the Ampere force, the left-hand rule works. This means, in order to understand where the Fl value is directed, you need to open the palm of your left hand so that the magnetic induction lines enter your hand, and the extended four fingers indicate the direction of the velocity vector. Then the thumb, bent at a right angle to the palm, indicates the direction of the Lorentz force. In the picture below you can see how to determine the direction.
Attention! The direction of the Lorentz action is perpendicular to the particle motion and the magnetic induction lines.
In this case, to be more precise, for positively and negatively charged particles the direction of the four unfolded fingers matters. The left-hand rule described above is formulated for a positive particle. If it is negatively charged, then the lines of magnetic induction should be directed not towards the open palm, but towards its back, and the direction of the vector Fl will be the opposite.
Now we will tell in simple words, what this phenomenon gives us and what real impact it has on the charges. Let us assume that the electron moves in a plane perpendicular to the direction of the magnetic induction lines. We have already mentioned that Fl does not affect the speed, but only changes the direction of particle motion. Then the Lorentz force will have a centripetal effect. This is reflected in the figure below.
Application
Of all the areas where the Lorentz force is used, one of the largest is the movement of particles in the earth's magnetic field. If we consider our planet as a large magnet, then the particles that are located near the north magnetic poles move in an accelerated spiral. As a result, they collide with atoms from upper layers atmosphere, and we see the northern lights.
However, there are other cases where this phenomenon applies. For example:
- Cathode ray tubes. In their electromagnetic deflection systems. CRTs have been used for more than 50 consecutive years in various devices, starting from the simplest oscilloscope to televisions different forms and sizes. It is curious that when it comes to color reproduction and working with graphics, some still use CRT monitors.
- Electrical machines – generators and motors. Although the Ampere force is more likely to act here. But these quantities can be considered as adjacent. However, these are complex devices during operation of which the influence of many physical phenomena is observed.
- In accelerators of charged particles in order to set their orbits and directions.
Conclusion
Let us summarize and outline the four main points of this article in simple language:
- The Lorentz force acts on charged particles that move in a magnetic field. This follows from the basic formula.
- It is directly proportional to the speed of the charged particle and magnetic induction.
- Does not affect particle speed.
- Affects the direction of the particle.
Its role is quite large in the “electrical” areas. A specialist should not lose sight of the basic theoretical information about the fundamental physical laws. This knowledge will be useful, as well as for those who are engaged in scientific work, design and simply for general development.
Now you know what the Lorentz force is, what it is equal to and how it acts on charged particles. If you have any questions, ask them in the comments below the article!
Materials
The emergence of a force acting on electric charge, moving in an external electromagnetic field
Animation
Description
The Lorentz force is the force acting on a charged particle moving in an external electromagnetic field.
The formula for the Lorentz force (F) was first obtained by generalizing the experimental facts of H.A. Lorentz in 1892 and presented in the work “Maxwell’s Electromagnetic Theory and Its Application to Moving Bodies.” It looks like:
F = qE + q, (1)
where q is a charged particle;
E - electric field strength;
B is the magnetic induction vector, independent of the size of the charge and the speed of its movement;
V is the velocity vector of a charged particle relative to the coordinate system in which the values of F and B are calculated.
The first term on the right side of equation (1) is the force acting on a charged particle in an electric field F E =qE, the second term is the force acting in a magnetic field:
F m = q. (2)
Formula (1) is universal. It is valid for both constant and variable force fields, as well as for any values of the velocity of a charged particle. It is an important relation of electrodynamics, since it allows us to connect the equations of the electromagnetic field with the equations of motion of charged particles.
In the nonrelativistic approximation, the force F, like any other force, does not depend on the choice of the inertial reference frame. At the same time, the magnetic component of the Lorentz force F m changes when moving from one reference system to another due to a change in speed, so the electrical component F E will also change. In this regard, dividing the force F into magnetic and electric makes sense only with an indication of the reference system.
In scalar form, expression (2) looks like:
Fm = qVBsina, (3)
where a is the angle between the velocity and magnetic induction vectors.
Thus, the magnetic part of the Lorentz force is maximum if the direction of motion of the particle is perpendicular to the magnetic field (a =p /2), and is equal to zero if the particle moves along the direction of field B (a =0).
The magnetic force F m is proportional to the vector product, i.e. it is perpendicular to the velocity vector of the charged particle and therefore does not do work on the charge. This means that in a constant magnetic field, under the influence of magnetic force, only the trajectory of a moving charged particle is bent, but its energy always remains the same, no matter how the particle moves.
The direction of the magnetic force for a positive charge is determined according to the vector product (Fig. 1).
Direction of force acting on a positive charge in a magnetic field
Rice. 1
For a negative charge (electron), the magnetic force is directed in the opposite direction (Fig. 2).
Direction of the Lorentz force acting on an electron in a magnetic field
Rice. 2
Magnetic field B is directed towards the reader perpendicular to the drawing. There is no electric field.
If the magnetic field is uniform and directed perpendicular to the speed, a charge of mass m moves in a circle. The radius of the circle R is determined by the formula:
where is the specific charge of the particle.
The period of revolution of a particle (the time of one revolution) does not depend on the speed if the speed of the particle is much less than the speed of light in vacuum. Otherwise, the particle's orbital period increases due to the increase in relativistic mass.
In the case of a non-relativistic particle:
where is the specific charge of the particle.
In a vacuum in a uniform magnetic field, if the velocity vector is not perpendicular to the magnetic induction vector (a№p /2), a charged particle under the influence of the Lorentz force (its magnetic part) moves along a helical line with a constant velocity V. In this case, its movement consists of a uniform rectilinear movement along the direction of the magnetic field B with speed and uniform rotational movement in a plane perpendicular to field B with speed (Fig. 2).
The projection of the trajectory of a particle onto a plane perpendicular to B is a circle of radius:
period of revolution of the particle:
The distance h that the particle travels in time T along the magnetic field B (step of the helical trajectory) is determined by the formula:
h = Vcos a T . (6)
The axis of the helix coincides with the direction of field B, the center of the circle moves along power line fields (Fig. 3).
Movement of a charged particle flying in at an angle a№p /2 in magnetic field B
Rice. 3
There is no electric field.
If the electric field E No. 0, the movement is more complex.
In the particular case, if the vectors E and B are parallel, during the movement the velocity component V 11, parallel to the magnetic field, changes, as a result of which the pitch of the helical trajectory (6) changes.
In the event that E and B are not parallel, the center of rotation of the particle moves, called drift, perpendicular to the field B. The drift direction is determined by the vector product and does not depend on the sign of the charge.
The influence of a magnetic field on moving charged particles leads to a redistribution of current over the cross section of the conductor, which is manifested in thermomagnetic and galvanomagnetic phenomena.
The effect was discovered by the Dutch physicist H.A. Lorenz (1853-1928).
Timing characteristics
Initiation time (log to -15 to -15);
Lifetime (log tc from 15 to 15);
Degradation time (log td from -15 to -15);
Time of optimal development (log tk from -12 to 3).
Diagram:
Technical implementations of the effect
Technical implementation of the Lorentz force
The technical implementation of an experiment to directly observe the effect of the Lorentz force on a moving charge is usually quite complex, since the corresponding charged particles have a characteristic molecular size. Therefore, observing their trajectory in a magnetic field requires evacuating the working volume to avoid collisions that distort the trajectory. So, as a rule, such demonstration installations are not created specifically. The easiest way to demonstrate this is to use a standard Nier sector magnetic mass analyzer, see Effect 409005, the action of which is entirely based on the Lorentz force.
Applying an effect
A typical use in technology is the Hall sensor, widely used in measurement technology.
A plate of metal or semiconductor is placed in a magnetic field B. When passing through it electric current density j in the direction perpendicular to the magnetic field, a transverse electric field arises in the plate, the intensity of which E is perpendicular to both vectors j and B. According to the measurement data, B is found.
This effect is explained by the action of the Lorentz force on a moving charge.
Galvanomagnetic magnetometers. Mass spectrometers. Charged particle accelerators. Magnetohydrodynamic generators.
Literature
1. Sivukhin D.V. General course of physics. - M.: Nauka, 1977. - T.3. Electricity.
2. Physical encyclopedic dictionary. - M., 1983.
3. Detlaf A.A., Yavorsky B.M. Physics course.- M.: graduate School, 1989.
Keywords
- electric charge
- magnetic induction
- a magnetic field
- electric field strength
- Lorentz force
- particle speed
- circle radius
- circulation period
- helical path pitch
- electron
- proton
- positron
Sections of natural sciences:
The effect exerted by a magnetic field on moving charged particles is very widely used in technology.
For example, the deflection of an electron beam in TV picture tubes is carried out using a magnetic field, which is created by special coils. A number of electronic devices use a magnetic field to focus beams of charged particles.
In currently created experimental installations for carrying out a controlled thermonuclear reaction, the action of a magnetic field on the plasma is used to twist it into a cord that does not touch the walls of the working chamber. The circular motion of charged particles in a uniform magnetic field and the independence of the period of such motion from the particle speed are used in cyclic accelerators of charged particles - cyclotrons.
The Lorentz force is also used in devices called mass spectrographs, which are designed to separate charged particles according to their specific charges.
The diagram of the simplest mass spectrograph is shown in Figure 1.
In chamber 1, from which air has been pumped out, there is an ion source 3. The chamber is placed in a uniform magnetic field, at each point of which the induction \(~\vec B\) is perpendicular to the plane of the drawing and directed towards us (in Figure 1 this field is indicated by circles) . An accelerating voltage is applied between the electrodes A and B, under the influence of which the ions emitted from the source are accelerated and at a certain speed enter the magnetic field perpendicular to the induction lines. Moving in a magnetic field in a circular arc, the ions fall on photographic plate 2, which makes it possible to determine the radius R this arc. Knowing the magnetic field induction IN and speed υ ions, according to the formula
\(~\frac q m = \frac (v)(RB)\)
the specific charge of ions can be determined. And if the charge of the ion is known, its mass can be calculated.
Literature
Aksenovich L. A. Physics in high school: Theory. Tasks. Tests: Textbook. allowance for institutions providing general education. environment, education / L. A. Aksenovich, N. N. Rakina, K. S. Farino; Ed. K. S. Farino. - Mn.: Adukatsiya i vyakhavanne, 2004. - P. 328.
Why does history include some scientists on its pages in golden letters, while others are erased without a trace? Everyone who comes to science is obliged to leave their mark on it. It is by the size and depth of this trace that history judges. Thus, Ampere and Lorentz made an invaluable contribution to the development of physics, which made it possible not only to develop scientific theories, but received significant practical value. How did the telegraph come about? What are electromagnets? Today's lesson will answer all these questions.
For science, the acquired knowledge is of great value, which can subsequently find its practical use. New discoveries not only expand research horizons, but also raise new questions and problems.
Let's highlight the main Ampere's discoveries in the field of electromagnetism.
Firstly, these are the interactions of conductors with current. Two parallel conductors with currents are attracted to each other if the currents in them are in the same direction, and repel if the currents in them are in the opposite direction (Fig. 1).
Rice. 1. Current carrying conductors
Ampere's law reads:
The force of interaction between two parallel conductors is proportional to the product of the currents in the conductors, proportional to the length of these conductors and inversely proportional to the distance between them.
The force of interaction between two parallel conductors,
The magnitude of currents in conductors,
− length of conductors,
Distance between conductors,
Magnetic constant.
The discovery of this law made it possible to introduce into units of measurement a current value that did not exist before that time. So, if we proceed from the definition of current strength as the ratio of the amount of charge transferred through cross section conductor per unit time, then we obtain a fundamentally unmeasurable quantity, namely the amount of charge transferred through the cross section of the conductor. Based on this definition, we will not be able to introduce a unit of current. Ampere's law allows us to establish a connection between the magnitudes of current in conductors and quantities that can be measured experimentally: mechanical force and distance. Thus, it is possible to introduce into consideration the unit of current - 1 A (1 ampere).
One ampere current - this is a current at which two homogeneous parallel conductors located in a vacuum at a distance of one meter from each other interact with Newton’s force.
Law of interaction of currents - two parallel conductors in a vacuum, the diameters of which are many less distances between them, interact with a force directly proportional to the product of the currents in these conductors and inversely proportional to the distance between them.
Another discovery of Ampere is the law of the action of a magnetic field on a current-carrying conductor. It is expressed primarily in the action of a magnetic field on a coil or frame with current. Thus, a coil with current in a magnetic field is acted upon by a moment of force, which tends to rotate this coil so that its plane becomes perpendicular to the lines of the magnetic field. The angle of rotation of the coil is directly proportional to the amount of current in the coil. If the external magnetic field in the coil is constant, then the value of the magnetic induction module is also constant. The area of the coil at not very high currents can also be considered constant; therefore, it is true that the current strength is equal to the product of the moment of the forces turning the coil with the current by a certain constant value under constant conditions.
– current strength,
– the moment of forces unwinding the coil with current.
Consequently, it becomes possible to measure the current strength by the angle of rotation of the frame, which is implemented in measuring device– ammeter (Fig. 2).
Rice. 2. Ammeter
After discovering the effect of a magnetic field on a current-carrying conductor, Ampere realized that this discovery could be used to make a conductor move in a magnetic field. So, magnetism can be turned into mechanical movement- create an engine. One of the first to operate on direct current was an electric motor (Fig. 3), created in 1834 by the Russian electrical engineer B.S. Jacobi.
Rice. 3. Engine
Let's consider a simplified model of a motor, which consists of a stationary part with magnets attached to it - the stator. Inside the stator, a frame of conductive material called a rotor can rotate freely. In order for electric current to flow through the frame, it is connected to the terminals using sliding contacts (Fig. 4). If you connect the motor to a source direct current into a circuit with a voltmeter, then when the circuit is closed, the frame with current will begin to rotate.
Rice. 4. Operating principle of the electric motor
In 1269, the French naturalist Pierre de Maricourt wrote a work entitled “Letter on the Magnet.” The main goal of Pierre de Maricourt was to create a perpetual motion machine, in which he was going to use amazing properties magnets. How successful his attempts were is unknown, but what is certain is that Jacobi used his electric motor to propel the boat, and he managed to accelerate it to a speed of 4.5 km/h.
It is necessary to mention one more device that works on the basis of Ampere's laws. Ampere showed that a current-carrying coil behaves like a permanent magnet. This means that it is possible to design electromagnet– a device whose power can be adjusted (Fig. 5).
Rice. 5. Electromagnet
It was Ampere who came up with the idea that by combining conductors and magnetic needles, one could create a device that transmits information over a distance.
Rice. 6. Electric telegraph
The idea of the telegraph (Fig. 6) arose in the very first months after the discovery of electromagnetism.
However, the electromagnetic telegraph became widespread after Samuel Morse created a more convenient device and, most importantly, developed a binary alphabet consisting of dots and dashes, which is called Morse code.
From the transmitting telegraph apparatus, using a “Morse key” that closes the electrical circuit, short or long electrical signals corresponding to dots or dashes of Morse code are generated in the communication line. On a receiving telegraph apparatus (writing instrument), while the signal (electric current) is passing, an electromagnet attracts an armature, to which a metal writing wheel or scribe is rigidly connected, which leaves an ink mark on the paper tape (Fig. 7).
Rice. 7. Telegraph operation diagram
The mathematician Gauss, when he became acquainted with Ampere's research, proposed creating an original cannon (Fig. 8), working on the principle of the action of a magnetic field on an iron ball - a projectile.
Rice. 8. Gauss gun
It is necessary to pay attention to the historical era in which these discoveries were made. In the first half of the 19th century, Europe took leaps and bounds along the path of the industrial revolution - it was a fertile time for scientific research discoveries and their rapid implementation into practice. Ampere undoubtedly made a significant contribution to this process, giving civilization electromagnets, electric motors and the telegraph, which are still in wide use today.
Let us highlight the main discoveries of Lorenz.
Lorentz established that a magnetic field acts on a particle moving in it, causing it to move along a circular arc:
The Lorentz force is a centripetal force perpendicular to the direction of velocity. First of all, the law discovered by Lorentz allows us to determine such the most important characteristic, as the ratio of charge to mass - specific charge.
The specific charge value is a value unique to each charged particle, which allows them to be identified, be it an electron, a proton or any other particle. Thus, scientists received a powerful research tool. For example, Rutherford was able to analyze radioactive radiation and identified its components, among which there are alpha particles - the nuclei of the helium atom - and beta particles - electrons.
In the twentieth century, accelerators appeared, the operation of which is based on the fact that charged particles are accelerated in a magnetic field. The magnetic field bends the trajectories of particles (Fig. 9). The direction of the bend of the trace allows one to judge the sign of the particle's charge; By measuring the radius of the trajectory, you can determine the speed of the particle if its mass and charge are known.
Rice. 9. Curvature of particle trajectory in a magnetic field
The Large Hadron Collider was developed on this principle (Fig. 10). Thanks to Lorenz's discoveries, science has received fundamentally new tool For physical research, opening the way to the world of elementary particles.
Rice. 10. Large Hadron Collider
In order to characterize the scientist’s influence on technological progress, let us remember that from the expression for the Lorentz force it follows that it is possible to calculate the radius of curvature of the trajectory of a particle moving in a constant magnetic field. Under constant external conditions, this radius depends on the mass of the particle, its speed and charge. Thus, we get the opportunity to classify charged particles according to these parameters and, therefore, we can analyze any mixture. If a mixture of substances in a gaseous state is ionized, accelerated and directed into a magnetic field, then the particles will begin to move along circular arcs with different radii - the particles will leave the field at different points, and all that remains is to fix these departure points, which is realized using a screen covered with a phosphor , which glows when charged particles hit it. This is exactly how it works mass analyzer(Fig. 11) . Mass analyzers are widely used in physics and chemistry to analyze the composition of mixtures.
Rice. 11. Mass analyzer
This is not all the technical devices that work on the basis of the developments and discoveries of Ampere and Lorentz, because scientific knowledge sooner or later ceases to be the exclusive property of scientists and becomes the property of civilization, while it is embodied in various technical devices, which make our life more comfortable.
Bibliography
- Kasyanov V.A., Physics 11th grade: Textbook. for general education institutions. - 4th ed., stereotype. - M.: Bustard, 2004. - 416 p.: ill., 8 l. color on
- Gendenstein L.E., Dick Yu.I., Physics 11. - M.: Mnemosyne.
- Tikhomirova S.A., Yarovsky B.M., Physics 11. - M.: Mnemosyne.
- Internet portal “Chip and Dip” ().
- Internet portal “Kiev City Library” ().
- Internet portal "Institute distance education» ().
Homework
1. Kasyanov V.A., Physics 11th grade: Textbook. for general education institutions. - 4th ed., stereotype. - M.: Bustard, 2004. - 416 p.: ill., 8 l. color on, st. 88, v. 1-5.
2. In a cloud chamber, which is placed in a uniform magnetic field with an induction of 1.5 Tesla, an alpha particle, flying perpendicular to the induction lines, leaves a trace in the form of a circular arc with a radius of 2.7 cm. Determine the momentum and kinetic energy particles. The mass of the alpha particle is 6.7∙10 -27 kg, and the charge is 3.2∙10 -19 C.
3. Mass spectrograph. A beam of ions, accelerated by a potential difference of 4 kV, flies into a uniform magnetic field with a magnetic induction of 80 mT perpendicular to the magnetic induction lines. The beam consists of two types of ions with molecular weights 0.02 kg/mol and 0.022 kg/mol. All ions have a charge of 1.6 ∙ 10 -19 C. The ions fly out of the field in two beams (Fig. 5). Find the distance between the beams of ions that fly out.
4. * Using a DC electric motor, the load is lifted on a cable. If you disconnect the electric motor from the voltage source and short-circuit the rotor, the load will descend at a constant speed. Explain this phenomenon. What form does the potential energy of the load go into?