Physics is not the best light object, especially for those who have problems with it. It's no secret that not everyone gets along with sign systems, there are people who need to touch or at least see what they are learning. Fortunately, in addition to formulas and boring books, there are visual ways. For example, in this article we will consider how to determine the direction of the electromagnetic force with the help of the hand, using the well-known left hand rule.
This rule makes it a little easier, if not understanding the laws, then at least solving problems. True, only those who are at least a little versed in physics and its terms can apply it. Many textbooks have an image that explains very clearly how to use the left hand rule when solving problems. Physics, however, is clearly not the kind of science where you often have to put your hand on visual models, so develop your imagination.
First you need to know the direction of current flow in the part of the circuit where you are going to apply the left hand rule. Remember that a mistake in determining the direction will show you the opposite direction of the electromagnetic force, which will automatically nullify all your further efforts and calculations. As soon as you determine the direction of the current, position your left palm so that this course is indicated.
Next, you need to find the direction of the vector. If you have problems with this, it is worth brushing up your knowledge with the help of textbooks. When you find the desired vector, turn your palm so that this vector enters the open palm of the same left hand. The whole difficulty in applying the left hand rule lies precisely in whether you can correctly apply your knowledge to find constant vectors.
When you are sure that your palm is properly positioned, pull back so that its position becomes perpendicular to the direction of the current (where the rest of the fingers of the bunch are pointing). Remember that a finger is far from the most accurate indicator in physics, and in this case it only shows an approximate direction. If you are interested in accuracy, then after applying the rule of the left hand, use a protractor to bring the angle between the direction of the current and the direction indicated by the thumb to 90 degrees.
It should be remembered that the rule in question is not suitable for accurate calculations - it can only serve to quickly determine the direction of the electromagnetic force. In addition, its use requires additional conditions of the problem, and therefore is not always applicable in practice.
Naturally, it is not always possible to have a hand in the object under study, because sometimes it does not exist at all (in theoretical problems). In this case, in addition to imagination, other methods should be used. For example, you can draw a diagram on paper and apply the left hand rule to the drawing. The hand itself can also be schematically depicted in the figure for greater clarity. The main thing is not to get confused otherwise you can make mistakes. Therefore, do not forget to mark all the lines with signatures - then it will be easier for you to figure it out yourself.
From experimental studies in physics, it can be concluded that the magnetic field has an effect on charged particles that are in motion, and, consequently, on current-carrying conductors. Force of influence magnetic field on a current-carrying conductor is called the Ampere force, and its vector direction establishes the left-hand rule.
The Ampere force is directly proportional to the induction of the magnetic field, the current strength in the conductor, the length of the conductor and the angle of the magnetic field vector with respect to the conductor. The mathematical writing of this dependence is called Ampère's law:
F A \u003d B * I * l * sinα
Based on this formula, we can conclude that at α=0° (parallel position of the conductor) the force F A will be zero, and at α=90° (perpendicular direction of the conductor) it will be maximum.
The properties of the force acting on a conductor with an electric current in a magnetic field were described in detail in the works of A. Ampère.
If the Ampere force acts on the entire conductor with a passing current (a stream of charged particles), then a separate moving positively charged particle is influenced by the Lorentz force. The Lorentz force can be expressed in terms of F A by dividing this value by the number of moving charges inside the conductor (the concentration of charge carriers).
In a magnetic field, under the influence of the Lorentz force, the charge moves in a circle, provided that the direction of its movement is perpendicular to the lines of induction.
The Lorentz force is calculated using the following formula:
F L \u003d q * v * B * sinα
After conducting a series of physical experiments using magnetic poles as a source of a uniform magnetic field. and loops with current, one can observe a change in the behavior of the loop (it is pushed or drawn into the zone of propagation of the magnetic field) when not only the direction of charged particles changes, but also when the orientation of the poles changes. Thus, the magnetic induction vector, the velocity vector of charged particles (current direction) and the force vector are in close interaction and are oriented mutually perpendicular.
To determine the direction of work of the Lorentz and Ampère forces, one should use the left hand rule: “If the palm of the left hand is turned so that the lines of the magnetic field enter it at a right angle, and the outstretched fingers are located in the direction of the electric current (the direction of movement of particles with a positive charge) , then the direction of the force will be indicated by the perpendicularly retracted thumb.
Such a simplified formulation allows you to quickly and accurately determine the direction of any unknown vector: strength, current, or lines of magnetic field induction.
The left hand rule applies when:
- the direction of the force on positively charged particles is determined (for negatively charged particles, the direction will be opposite);
- the lines of induction of the magnetic field and the velocity vector of charged particles form an angle other than zero (otherwise the force will not act on the conductor).
In a uniform magnetic field, the frame with current is located so that the lines of the magnetic field pass through its plane at a right angle.
If a magnetic field is formed around a linear conductor with current, then it is considered non-uniform (variable in time and space). In such a field, the current-carrying frame will not only be oriented in a certain way, but will also be attracted to the current-carrying conductor or pushed out of the magnetic field. The behavior of the loop is determined by the direction of the currents in the conductor and the loop. The frame with current always rotates along the radius of the induction lines of the inhomogeneous magnetic field.
If we consider two conductors with currents moving in the same direction, then using the left hand rule, it can be established that the force acting on the right conductor will be directed to the left, while the force acting on the left conductor will be directed to the right. Therefore, it turns out that the forces acting on the conductors are directed towards each other. It is this conclusion that explains the attraction of conductors with unidirectional currents.
If the current in two parallel conductors will go in opposite directions, then the acting forces will be directed in different directions. This will repel the two conductors.
A loop with a current placed in a non-uniform magnetic field is subjected to the action of forces in different directions, causing it to rotate. On this phenomenon, the principle of operation of the electric motor is based.
The application of the left hand rule is of great practical importance and is the result of repeated experiments that reveal the nature of the magnetic field.
Left hand rule video
Since the creation of electricity, a lot of scientific work has been done in physics to study its characteristics, features and influence on environment. The gimlet rule has made its significant mark on the study of the magnetic field, the law right hand for a cylindrical winding of a wire, it allows a deeper understanding of the processes taking place in a solenoid, and the left-hand rule characterizes the forces that affect a current-carrying conductor. Thanks to the right and left hands, as well as mnemonic techniques, these patterns can be easily studied and understood.
gimlet principle
For quite a long time, the magnetic and electrical characteristics of the field were studied separately by physics. However, in 1820, quite by accident, the Danish scientist Hans Christian Oersted discovered the magnetic properties of a wire with electricity during a lecture on physics at the university. The dependence of the orientation of the magnetic needle on the direction of current flow in the conductor was also found.
The conducted experiment proves the presence of a field with magnetic characteristics around a current-carrying wire, to which a magnetized needle or compass reacts. The orientation of the flow of the "change" makes the compass needle turn in opposite directions, the arrow itself is located tangentially to the electromagnetic field.
To identify the orientation of electromagnetic flows, the gimlet rule is used, or the law of the right screw, which states that by screwing the screw along the course of the flow of electric current in the shunt, the way the handle is rotated will set the orientation of the EM flows of the "change" background.
It is also possible to use Maxwell's rule of the right hand: when the retracted finger of the right hand is oriented along the course of the flow of electricity, then the remaining clenched fingers will show the orientation of the electromagnetic field.
Using these two principles, the same effect will be obtained, used to determine electromagnetic fluxes.
Right hand law for solenoid
The considered screw principle or Maxwell's regularity for the right hand is applicable to a straight wire with current. However, in electrical engineering there are devices in which the conductor is not located straight, and the law of the screw is not applicable to it. First of all, this applies to inductors and solenoids. A solenoid, as a kind of inductor, is a cylindrical winding of wire, the length of which is many times greater than the diameter of the solenoid. The inductor inductor differs from the solenoid only in the length of the conductor itself, which can be several times smaller.
French mathematician and Physics A-M. Ampere, thanks to his experiments, found out and proved that when an electric current passed through the inductor, the compass pointers at the ends of the cylindrical winding of the wire turned their reverse ends along the invisible flows of the EM field. Such experiments proved that a magnetic field is formed near the inductor with current, and the cylindrical winding of the wire forms magnetic poles. The electromagnetic field excited by the electric current of the cylindrical winding of the wire is similar to the magnetic field of a permanent magnet - the end of the cylindrical winding of the wire, from which the EM fluxes emerge, represents the north pole, and the opposite end is the south.
To recognize the magnetic poles and the orientation of the EM lines in the inductor with current, the right-hand rule for the solenoid is used. It says that if you take this coil with your hand, place the fingers of the palm directly in the course of the flow of electrons in the turns, the thumb, moved ninety degrees, will set the orientation of the electromagnetic background in the middle of the solenoid - its north pole. Accordingly, knowing the position of the magnetic poles of the cylindrical winding of the wire, it is possible to determine the path of electron flow in the turns.
left hand law
Hans Christian Oersted, after discovering the phenomenon of a magnetic field near a shunt, quickly shared his results with most scientists in Europe. As a result, Ampere A.-M., using his own methods, after a short period of time revealed to the public an experiment on the specific behavior of two parallel shunts with electric current. The formulation of the experiment proved that wires placed in parallel, through which electricity flows in one direction, mutually move towards each other. Accordingly, such shunts will repel each other, provided that the “change” flowing in them will be distributed in different directions. These experiments formed the basis of Ampère's laws.
Tests allow us to voice the main conclusions:
- A permanent magnet, a "reversible" conductor, an electrically charged moving particle have an EM region around them;
- A charged particle moving in this region is subject to some influence from the EM background;
- Electrical "reversal" is the oriented movement of charged particles, respectively, the electromagnetic background acts on the shunt with electricity.
The EM background influences the shunt with a "change" of some kind of pressure called the Ampère force. This characteristic can be determined by the formula:
FA=IBΔlsinα, where:
- FA is the Ampere force;
- I is the intensity of electricity;
- B is the vector of magnetic induction modulo;
- Δl is the shunt size;
- α is the angle between direction B and the course of electricity in the wire.
Provided that the angle α is ninety degrees, then this force is the largest. Accordingly, if this angle is zero, then the force is zero. The contour of this force is revealed by the pattern of the left hand.
If you study the gimlet rule and the left hand rule, you will get all the answers to the formation of EM fields and their effect on conductors. Thanks to these rules, it is possible to calculate the inductance of the coils and, if necessary, form countercurrents. The principle of construction of electric motors is based on the Ampère forces in general and the left hand rule in particular.
Video
The magnetic field and its graphic representationGimlet rule
Line direction
magnetic field current is associated with
direction of current in the conductor.
gimlet rule
if direction
forward movement
gimlet matches with
direction of current in
conductor, then the direction
gimlet handle rotation
coincides with the direction
magnetic field lines.
Using the gimlet rule
in the direction of current
determine the directions of the lines
the magnetic field created by this
current, but in the direction of the lines
magnetic field -
the direction of the current that creates
this field.
Inhomogeneous and uniform magnetic field
Conductor with current is located1. Direction of electric current away from us
(in the plane of the sheet)
Lines of magnetic
fields will
sent to
clockwise
gimlet rule
Conductor with current is locatedperpendicular to the plane of the sheet:
2.Direction of electric current towards us
(from sheet plane)
Lines of magnetic
fields will
directed against
clockwise
The conductor with current is located perpendicular to the plane of the sheet: 1. The direction of the electric current from us (to the plane of the sheet) According to the rights
Right hand ruleFor determining
direction of magnetic lines
solenoid fields are more convenient
use another rule
which is sometimes called
right hand rule.
if you grab the solenoid
palm of the right hand,
pointing four fingers at
the direction of the current in the turns,
then set aside big
the finger will show the direction
magnetic field lines
inside the solenoid.
The conductor with current is located perpendicular to the plane of the sheet: 2. Direction of electric current to us (from the plane of the sheet) According to the
A solenoid, like a magnet, has poles:that end of the solenoid from which the magnetic lines
out is called the north pole, and the one in
which are included - southern.
Knowing the direction of the current in the solenoid,
right hand rule can be defined
the direction of the magnetic lines inside it, and
that means his magnetic poles and vice versa.
The right hand rule can also be applied to
determining the direction of magnetic field lines
in the center of a single coil
with current.
Right hand rule
Forconductor with current
If the right hand
arrange so
to thumb
was sent to
current, then the rest
four fingers
show direction
magnetic lines
induction 1. A magnetic field is created...
2. What does the picture of magnetic lines show?
3. Give a characteristic of a uniform magnetic field.
Execute the drawing.
4. Give a characteristic of an inhomogeneous magnetic
fields. Execute the drawing.
5. Draw a uniform magnetic field in
depending on the direction of the magnetic lines.
Explain.
6. Explain the principle of the gimlet rule.
7. Indicate two cases of direction dependency
magnetic lines from the direction of the electric current.
8. What rule should be used for
determining the direction of magnetic lines
solenoid. What is it?
9. How to determine the poles of the solenoid?
Right hand rule for a conductor with current
Magnetic field detectionby its effect on
electricity.
Left hand rule.
1. A magnetic field is created ... 2. What does the picture of magnetic lines show? 3. Give a characteristic of a uniform magnetic field. Run dash
For every conductor with current,placed in a magnetic field and
not matching his
magnetic lines, this field
acts with some force.
Detection of a magnetic field by its effect on an electric current. Left hand rule.
Conclusions:The magnetic field is created by an electric
current and is detected by its action
to electric current.
Direction of current in a conductor
the direction of the magnetic field lines and
direction of the force acting on
conductor, interconnected.
For any conductor with current placed in a magnetic field and not coinciding with its magnetic lines, this field acts with some force.
left hand ruledirection of force,
acting on the conductor with
current in a magnetic field
determine using
left hand rule.
If the left hand is placed
so that the lines of the magnetic
fields entered the palm
perpendicular to it, and four
fingers pointed at
current. That set aside by 900
thumb will show
direction of the current
to the conductor of power.
Conclusions:
For the direction of the current in the externalchain taken direction from "+"
to "-", i.e. against direction
movement of electrons in a circuit
left hand rule
Determining the strength of AmpereIf the left hand is placed
so that the magnetic vector
induction entered the palm, and
outstretched fingers were
directed along the current
abducted thumb
indicate the direction of action
Ampere force on a conductor with
current.
For the direction of the current in the external circuit, the direction from "+" to "-" is taken, i.e. against the direction of movement of electrons in the circuit
The left hand rule can be appliedto determine the direction of force, with
which the magnetic field acts on
individual moving
charged particles.
Determining the strength of Ampere
Force acting on a chargeIf the left hand
arrange so that the lines
magnetic field were included in
palm perpendicular to it,
and four fingers were
directed in motion
positively charged
particles (or against the movement
negatively charged)
set aside by 900 large
the finger will show the direction
force acting on the particle
Lorenz.
The left hand rule can be used to determine the direction of the force with which a magnetic field acts on individual moving charges.
Using the left hand ruledirection can be determined
current, direction of magnetic
lines, charge sign moving
particles.
Force acting on a charge
The case when the force of actionmagnetic field on the conductor with
current or moving
charged particle F=0
Using the left hand rule, you can determine the direction of the current, the direction of the magnetic lines, the sign of the charge of a moving particle.
Solve the problem:The case when the force of the magnetic field on a current-carrying conductor or a moving charged particle F=0
Solve the problem:
negatively charged particlemoving at a speed v in a magnetic
field. Make the same drawing
notebooks and point with an arrow
the direction of the force with which the field
acts on the particle.
The magnetic field acts with a force F on
particle moving with speed v.
Determine the sign of the charge of the particle.
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