> Magnetic field lines
How to determine magnetic field lines: diagram of the strength and directions of the magnetic field lines, using a compass to determine magnetic poles, drawing.
Magnetic field lines useful for visualizing the strength and direction of a magnetic field.
Learning challenge
- Relate the strength of the magnetic field to the density of the lines of the magnetic field.
Key points
- The direction of the magnetic field displays the compass arrows touching the magnetic field lines at any specified point.
- The B-field strength is inversely proportional to the distance between the lines. It is also exactly proportional to the number of lines per unit area. One line never crosses another.
- The magnetic field is unique at every point in space.
- Lines are uninterrupted and create closed loops.
- The lines run from the north to the south pole.
Terms
- Magnetic field lines are a graphical representation of the magnitude and direction of the magnetic field.
- B-field is a synonym for magnetic field.
Magnetic field lines
It is said that as a child, Albert Einstein loved to stare at a compass, reflecting on how a needle feels power without direct physical contact. Deep thinking and serious interest led to the fact that the child grew up and created his revolutionary theory of relativity.
Since magnetic forces affect distances, we calculate magnetic fields to represent these forces. Plotting lines is useful for visualizing the strength and direction of a magnetic field. The elongation of the lines indicates the north orientation of the compass needle. Magnetic is called B-field.
(a) - If a small compass is used to compare the magnetic field around a bar magnet, it will show the desired direction from north to south. (b) - Adding arrows creates continuous magnetic field lines. Strength is proportional to the proximity of the lines. (c) - If you can examine the interior of the magnet, then the lines will be displayed as closed loops
There is nothing difficult in comparing the magnetic field of an object. First, calculate the strength and direction of the magnetic field in several places. Mark these points with vectors pointing in the direction of the local magnetic field with a magnitude proportional to its strength. You can combine arrows to form magnetic field lines. The direction at any point will appear parallel to the direction of the nearest field lines, and the local density can be proportional to the strength.
Lines of force magnetic fields resemble contour on topographic maps, since they show something continuous. Many laws of magnetism can be formulated using simple concepts, like the number of field lines through the surface.
The direction of the magnetic field lines represented by the alignment of iron filings on paper positioned above the bar magnet
Various phenomena affect the display of lines. For example, iron filings on a magnetic field line create lines that correspond to magnetic ones. They are also visually displayed in the aurora borealis.
A small compass sent out into the field is aligned parallel to the field line and the North Pole points to V.
Miniature compasses can be used to show fields. (a) - The magnetic field of a circular current loop resembles a magnetic one. (b) - A long and straight wire forms a field with magnetic field lines creating circular loops. (c) - When the wire is in the plane of the paper, the field is perpendicular to the paper. Note which characters are used for the inward and outward-pointing field
A detailed study of magnetic fields helped to derive a number of important rules:
- The direction of the magnetic field touches the field line at any point in space.
- The field strength is proportional to the proximity of the line. It is also exactly proportional to the number of lines per unit area.
- The lines of the magnetic field never collide, which means that at any point in space the magnetic field will be unique.
- The lines remain continuous and follow from the north to the south pole.
The last rule is based on the fact that the poles cannot be split. And it's different from the lines electric field, in which the end and the beginning are marked by positive and negative charges.
About two and a half thousand years ago, people discovered that some natural stones have the ability to attract iron to themselves. This property was explained by the presence of a living soul in these stones, and a kind of "love" for iron.
Today we already know that these stones are natural magnets, and the magnetic field, and not at all a special disposition to the iron, creates these effects. A magnetic field is a special type of matter that is different from matter and exists around magnetized bodies.
Permanent magnets
Natural magnets, or magnetites, are not very magnetic. But man has learned to create artificial magnets with a much greater magnetic field strength. They are made from special alloys and magnetized by an external magnetic field. And then you can use them yourself.
Magnetic field lines
Any magnet has two poles, they were called the north and south poles. At the poles, the concentration of the magnetic field is maximum. But between the poles, the magnetic field is also not randomly located, but in the form of stripes or lines. They are called magnetic field lines. Finding them is quite simple - just place scattered iron filings in a magnetic field and shake them slightly. They will not be positioned as you like, but form, as it were, a pattern of lines starting at one pole and ending at the other. These lines seem to go out of one pole and enter the other.
Iron filings in the field of a magnet are themselves magnetized and are placed along the magnetic lines of force. This is how the compass functions. Our planet is a big magnet. The compass needle catches the Earth's magnetic field and, turning, is located along the lines of force, with one end pointing to the north magnetic pole, the other to the south. The Earth's magnetic poles are slightly different from the geographic ones, but when traveling away from the poles, it does not really matter, and you can consider them to be the same.
Variable magnets
The field of application of magnets in our time is extremely wide. They can be found inside electric motors, telephones, speakers, and radios. Even in medicine, for example, when a person swallows a needle or other iron object, it can be removed without surgery with a magnetic probe.
When connected to two parallel conductors of electrical current, they will attract or repel, depending on the direction (polarity) of the connected current. This is due to the appearance of a special kind of matter around these conductors. This matter is called the magnetic field (MF). Magnetic force is the force with which the conductors act on each other.
The theory of magnetism originated in antiquity, in the ancient civilization of Asia. In Magnesia, a special breed was found in the mountains, pieces of which could be attracted to each other. According to the name of the place, this breed was called "magnets". The bar magnet contains two poles. At the poles, its magnetic properties.
A magnet hanging on a string will show the sides of the horizon with its poles. Its poles will be turned north and south. The compass device operates on this principle. The opposite poles of two magnets attract, and the like poles repel.
Scientists have found that a magnetized arrow near a conductor deflects when an electric current passes through it. This suggests that an MP is formed around it.
The magnetic field affects:
Moving electric charges.
Substances called ferromagnets: iron, cast iron, their alloys.
Permanent magnets are bodies that have a common magnetic moment of charged particles (electrons).
1 - South pole of the magnet
2 - North pole of magnet
3 - MP by the example of metal filings
4 - Direction of the magnetic field
Lines of force appear when a permanent magnet approaches a paper sheet on which a layer of iron filings is poured. The figure clearly shows the locations of the poles with oriented lines of force.
Sources of magnetic field
- Time-varying electric field.
- Mobile charges.
- Permanent magnets.
Since childhood, we have known permanent magnets. They were used as toys that attracted various metal parts... They were attached to the refrigerator, they were embedded in various toys.
Electric charges that are in motion tend to have more magnetic energy than permanent magnets.
Properties
- The main hallmark and the property of the magnetic field is relativity. If you leave a charged body motionless in a certain frame of reference, and place a magnetic needle next to it, it will point to the north, and at the same time will not "feel" an extraneous field, except for the earth's field. And if the charged body begins to move near the arrow, then an MP will appear around the body. As a result, it becomes clear that the MF is formed only when a certain charge moves.
- The magnetic field is able to influence and influence electricity... It can be detected by monitoring the movement of charged electrons. In a magnetic field, particles with a charge will deflect, conductors with a flowing current will move. The frame with the current supply connected will begin to rotate, and the magnetized materials will move a certain distance. The compass arrow is most often colored in blue color... It is a strip of magnetized steel. The compass is always oriented to the north, since the Earth has an MP. The whole planet is like a big magnet with its poles.
The magnetic field is not perceived by human organs, and can only be recorded with special devices and sensors. It can be variable and constant form... An alternating field is usually created by special inductors that function from alternating current... A constant field is formed by a constant electric field.
rules
Consider the basic rules for depicting a magnetic field for various conductors.
Gimlet rule
The line of force is drawn in a plane that is located at an angle of 90 0 to the path of current movement in such a way that at each point the force is directed tangentially to the line.
To determine the direction of the magnetic forces, you need to remember the rule of the right-hand gimbal.
The drill should be positioned along the same axis with the current vector, the handle should be rotated so that the drill would move in the direction of its direction. In this case, the orientation of the lines is determined by rotating the gimbal handle.
Ring gimbal rule
The translational movement of the gimbal in the conductor, made in the form of a ring, shows how the induction is oriented, the rotation coincides with the current flow.
The lines of force have their continuation inside the magnet and cannot be open.
The magnetic fields of different sources are summed up with each other. In doing so, they create a common field.
Magnets with the same poles repel, and those with different ones attract. The value of the strength of interaction depends on the distance between them. As the poles approach, the force increases.
Magnetic field parameters
- Concatenation of threads ( Ψ ).
- The vector of magnetic induction ( V).
- Magnetic flux ( F).
The intensity of the magnetic field is calculated by the size of the magnetic induction vector, which depends on the force F, and is formed by the current I along a conductor having a length l: B = F / (I * l).
Magnetic induction is measured in Tesla (T), in honor of the scientist who studied the phenomena of magnetism and was engaged in their calculation methods. 1 T is equal to the induction of the magnetic flux by the force 1 N at length 1m straight conductor at an angle 90 0 to the direction of the field, with a current of one ampere:
1 T = 1 x H / (A x m).
Left hand rule
The rule finds the direction of the magnetic induction vector.
If the palm of the left hand is placed in the field so that the magnetic field lines enter the palm from the North Pole at 90 0, and 4 fingers are placed along the current flow, thumb will show the direction of the magnetic force.
If the conductor is at a different angle, then the force will directly depend on the current and the projection of the conductor onto a plane at right angles.
The force does not depend on the type of conductor material and its cross section. If there is no conductor, and the charges move in a different medium, then the force will not change.
When the direction of the magnetic field vector in one direction of the same magnitude, the field is called uniform. Different environments affect the size of the induction vector.
Magnetic flux
The magnetic induction passing over a certain area S and limited to this area is a magnetic flux.
If the area has a slope at some angle α to the induction line, magnetic flux decreases by the size of the cosine of this angle. Its largest value is formed when the area is located at a right angle to the magnetic induction:
F = B * S.
The magnetic flux is measured in a unit such as "Weber", which is equal to the flow of induction by the value 1 T by area in 1 m 2.
Flux linkage
This concept is used to create overall value magnetic flux, which is created from a number of conductors located between the magnetic poles.
In the case when the same current I flows through the winding with the number of turns n, the total magnetic flux formed by all the turns is flux linkage.
Flux linkage Ψ measured in webers, and equal to: Ψ = n * Ф.
Magnetic properties
Permeability determines how much the magnetic field in a particular environment is lower or higher than the induction of the field in a vacuum. A substance is called magnetized if it forms its own magnetic field. When a substance is placed in a magnetic field, it becomes magnetized.
Scientists have identified the reason why bodies get magnetic properties. According to the hypothesis of scientists, inside substances there are electric currents of microscopic magnitude. The electron has its own magnetic moment, which has a quantum nature, moves along a certain orbit in atoms. It is these small currents that determine the magnetic properties.
If currents move randomly, then the magnetic fields caused by them are self-compensating. The external field makes the currents ordered, therefore a magnetic field is formed. This is the magnetization of the substance.
Various substances can be classified according to the properties of interaction with magnetic fields.
They are divided into groups:
Paramagnets- substances with properties of magnetization in the direction of the external field, with a low possibility of magnetism. They have a positive field strength. These substances include ferric chloride, manganese, platinum, etc.
Ferrimagnets- substances with magnetic moments unbalanced in direction and value. They are characterized by the presence of uncompensated antiferromagnetism. Field strength and temperature affect their magnetic susceptibility (various oxides).
Ferromagnets- Substances with increased positive susceptibility, depending on tension and temperature (crystals of cobalt, nickel, etc.).
Diamagnetics- have the property of magnetization in the opposite direction of the external field, that is, a negative value of the magnetic susceptibility, independent of the strength. In the absence of a field, this substance will not have magnetic properties. These substances include: silver, bismuth, nitrogen, zinc, hydrogen and other substances.
Antiferromagnets
- have a balanced magnetic moment, as a result of which a low degree of magnetization of the substance is formed. When heated, they undergo a phase transition of the substance, in which paramagnetic properties arise. When the temperature drops below a certain limit, such properties will not appear (chromium, manganese).
The considered magnets are also classified into two more categories:
Soft magnetic materials
... They have a low coercive force. In low-power magnetic fields, they can saturate. During the process of magnetization reversal, they have insignificant losses. As a result, such materials are used for the production of cores. electrical devices operating on alternating voltage (, generator,).
Magnetically hard materials. They have an increased value of the coercive force. A strong magnetic field is required to re-magnetize them. Such materials are used in the production of permanent magnets.
The magnetic properties of various substances are used in technical projects and inventions.
Magnetic circuits
The combination of several magnetic substances is called a magnetic circuit. They are similarities and are defined by similar laws of mathematics.
On the basis of magnetic circuits, electrical devices, inductance,. In a functioning electromagnet, the flow flows through a magnetic circuit made of a ferromagnetic material and air, which is not a ferromagnet. The combination of these components is a magnetic circuit. Many electrical devices contain magnetic circuits in their design.
Themes of the USE codifier: interaction of magnets, magnetic field of a conductor with current.
The magnetic properties of a substance have been known to people for a long time. The magnets got their name from the ancient city of Magnesia: a mineral (later called magnetic iron ore or magnetite) was distributed in its vicinity, pieces of which attracted iron objects.
Interaction of magnets
On both sides of each magnet there are North Pole and South Pole ... Two magnets are attracted to each other by opposite poles and repelled by the same ones. Magnets can act on each other even through a vacuum! All this resembles the interaction of electric charges, however the interaction of magnets is not electrical... This is evidenced by the following experimental facts.
The magnetic force is weakened when the magnet is heated. The force of interaction of point charges does not depend on their temperature.
The magnetic force is weakened by shaking the magnet. Nothing of the kind happens with electrically charged bodies.
Positive electrical charges can be separated from negative ones (for example, when electrifying bodies). But dividing the poles of the magnet does not work: if you cut the magnet into two parts, then poles also appear at the cut, and the magnet splits into two magnets with opposite poles at the ends (oriented in the same way as the poles of the original magnet).
So the magnets always bipolar, they exist only in the form dipoles... Isolated magnetic poles (so called magnetic monopoles- analogs electric charge) does not exist in nature (in any case, they have not yet been discovered experimentally). This is perhaps the most impressive asymmetry between electricity and magnetism.
Like electrically charged bodies, magnets act on electrical charges. However, the magnet only acts on moving charge; if the charge is at rest relative to the magnet, then the effect of the magnetic force on the charge is not observed. On the contrary, an electrified body acts on any charge, regardless of whether it is at rest or in motion.
By modern ideas the theory of short-range action, the interaction of magnets is carried out by magnetic field Namely, a magnet creates a magnetic field in the surrounding space, which acts on another magnet and causes a visible attraction or repulsion of these magnets.
An example of a magnet is magnetic needle compass. Using the magnetic arrow, you can judge the presence of a magnetic field in a given area of space, as well as the direction of the field.
Our planet Earth is a giant magnet. Not far from the north geographic pole of the Earth is the south magnetic pole. Therefore, the north end of the compass needle, turning to the south magnetic pole of the Earth, points to the geographic north. Hence, in fact, the name "north pole" of the magnet arose.
Magnetic field lines
The electric field, we recall, is investigated with the help of small test charges, by the action on which one can judge the magnitude and direction of the field. The analogue of a test charge in the case of a magnetic field is a small magnetic needle.
For example, you can get some geometric idea of the magnetic field by placing very small compass arrows at different points in space. Experience shows that the arrows will line up along certain lines - the so-called magnetic field lines... We will give the definition of this concept in the form of the following three points.
1. Magnetic field lines, or magnetic lines of force, are directed lines in space that have the following property: a small compass arrow placed at each point of such a line is oriented tangentially to this line.
2. The direction of the magnetic field line is the direction of the northern ends of the compass arrows located at the points of this line..
3. The denser the lines go, the stronger the magnetic field in a given area of space..
Iron filings can successfully play the role of compass arrows: in a magnetic field, small sawdust is magnetized and behaves exactly like magnetic arrows.
So, having poured iron filings around a permanent magnet, we will see approximately the following picture of the magnetic field lines (Fig. 1).
Rice. 1. Field of a permanent magnet
The north pole of the magnet is indicated in blue and a letter; the south pole - in red and a letter. Please note that the field lines go out from the north pole of the magnet and enter the south pole: after all, it is to the south pole of the magnet that the north end of the compass needle will be directed.
Oersted's experience
Despite the fact that electrical and magnetic phenomena have been known to people since antiquity, there is no relationship between them. long time was not observed. For several centuries, research on electricity and magnetism proceeded in parallel and independently of each other.
The remarkable fact that electrical and magnetic phenomena are actually related to each other was first discovered in 1820 - in the famous experiment of Oersted.
The scheme of Oersted's experiment is shown in Fig. 2 (image from the site rt.mipt.ru). Above the magnetic needle (and are the north and south poles of the arrow) there is a metal conductor connected to a current source. If you close the circuit, then the arrow turns perpendicular to the conductor!
This simple experience directly pointed to the relationship between electricity and magnetism. The experiments that followed Oersted's experiment firmly established the following pattern: the magnetic field is generated by electric currents and acts on currents.
Rice. 2. Oersted's experience
The pattern of the lines of the magnetic field generated by a conductor with current depends on the shape of the conductor.
Magnetic field of a straight wire with current
The magnetic field lines of a straight wire with current are concentric circles. The centers of these circles lie on the wire, and their planes are perpendicular to the wire (Fig. 3).
Rice. 3. Field of a straight wire with current
There are two alternative rules for determining the direction of forward current magnetic field lines.
Clockwise rule. The field lines go counterclockwise when viewed so that the current flows towards us.
Screw rule(or gimlet rule, or corkscrew rule- that's closer to someone ;-)). The lines of the field go where you need to rotate the screw (with a normal right-hand thread) so that it moves along the thread in the direction of the current.
Use whichever rule you like best. It is better to get used to the hour hand rule - you yourself will later see that it is more universal and easier to use (and then with gratitude remember it in your first year when you study analytical geometry).
In fig. 3, something new has also appeared: this is a vector called magnetic induction, or magnetic induction... The magnetic induction vector is an analogue of the electric field strength vector: it serves power characteristic magnetic field, determining the force with which the magnetic field acts on moving charges.
We will talk about the forces in a magnetic field later, but for now we will only note that the magnitude and direction of the magnetic field is determined by the vector of magnetic induction. At each point in space, the vector is directed to the same direction as the northern end of the compass arrow placed at this point, namely, tangentially to the field line in the direction of this line. The magnetic induction is measured in teslah(T).
As in the case of an electric field, the magnetic induction is superposition principle... It lies in the fact that the inductions of magnetic fields created at a given point by various currents are added vectorially and give the resulting vector of magnetic induction:.
Magnetic field of a loop with current
Consider a circular loop through which a direct current circulates. The source that creates the current is not shown in the figure.
The pattern of the field lines of our loop will look approximately as follows (Fig. 4).
Rice. 4. Field of the loop with current
It will be important for us to be able to determine in which half-space (relative to the plane of the loop) the magnetic field is directed. Again, we have two alternative rules.
Clockwise rule. Field lines go where the current appears to be circulating counterclockwise.
Screw rule. The field lines go where the screw (with a normal right-hand thread) will move if you rotate it in the direction of the current.
As you can see, the current and field are reversed compared to the formulations of these rules for the case of direct current.
Magnetic field of the coil with current
Coil it will turn out, if tightly, turn to turn, wind the wire in a sufficiently long spiral (Fig. 5 - image from the site en.wikipedia.org). There can be several tens, hundreds, or even thousands of turns in a coil. The coil is also called solenoid.
Rice. 5. Coil (solenoid)
The magnetic field of one turn, as we know, does not look very simple. Fields? individual turns of the coil are superimposed on each other, and, it would seem, the result should be a very confusing picture. However, this is not the case: the field of a long coil has unexpectedly simple structure(fig. 6).
Rice. 6.Coil field with current
In this figure, the current in the coil goes counterclockwise when viewed from the left (this will be the case if in Fig. 5 the right end of the coil is connected to the "plus" of the current source, and the left end to the "minus"). We see that the magnetic field of the coil has two characteristic properties.
1. Inside the coil, away from its edges, the magnetic field is homogeneous: at each point, the magnetic induction vector is the same in magnitude and direction. Field lines are parallel straight lines; they only bend near the edges of the coil when they come out.
2. Outside the coil, the field is close to zero. The more turns in the coil, the weaker the field outside it.
Note that an infinitely long coil does not emit a field at all: there is no magnetic field outside the coil. Inside such a coil, the field is everywhere uniform.
Doesn't it look like anything? The coil is a "magnetic" analogue of a capacitor. Remember that a capacitor creates a homogeneous electric field, whose lines are bent only near the edges of the plates, and outside the capacitor the field is close to zero; a capacitor with infinite plates does not release the field outside at all, and the field is uniform everywhere inside it.
And now - the main observation. Please compare the picture of the magnetic field lines outside the coil (Fig. 6) with the magnetic field lines in Fig. 1 . The same thing, isn't it? And now we come to a question that probably arose in your mind long ago: if a magnetic field is generated by currents and acts on currents, then what is the reason for the appearance of a magnetic field near a permanent magnet? After all, this magnet does not seem to be a conductor with current!
Ampere's hypothesis. Elementary currents
At first, it was thought that the interaction of magnets was due to special magnetic charges concentrated at the poles. But, unlike electricity, no one could isolate the magnetic charge; after all, as we have already said, it was not possible to obtain separately the north and south poles of the magnet - the poles are always present in the magnet in pairs.
Doubts about magnetic charges aggravated the experience of Oersted when it turned out that the magnetic field is generated by an electric current. Moreover, it turned out that for any magnet it is possible to select a conductor with a current of the appropriate configuration, such that the field of this conductor coincides with the field of the magnet.
Ampere put forward a bold hypothesis. There are no magnetic charges. The action of a magnet is explained by the closed electric currents inside it..
What are these currents? These elementary currents circulate inside atoms and molecules; they are associated with the movement of electrons in atomic orbits. The magnetic field of any body is made up of the magnetic fields of these elementary currents.
Elementary currents can be randomly located relative to each other. Then their fields are mutually extinguished, and the body does not exhibit magnetic properties.
But if the elementary currents are arranged in concert, then their fields, adding up, reinforce each other. The body becomes a magnet (Fig. 7; the magnetic field will be directed at us; the north pole of the magnet will also be directed at us).
Rice. 7. Elementary currents of the magnet
Ampere's hypothesis of elementary currents clarified the properties of magnets. Heating and shaking a magnet destroys the order of its elementary currents, and the magnetic properties weaken. The inseparability of the poles of the magnet became obvious: in the place of the cut of the magnet, we get the same elementary currents at the ends. The ability of a body to magnetize in a magnetic field is explained by the coordinated alignment of elementary currents, "turning" properly (read about the rotation of circular current in a magnetic field in the next leaflet).
Ampere's hypothesis turned out to be correct - this showed the further development of physics. The concept of elementary currents became an integral part of the theory of the atom, developed already in the twentieth century - almost a hundred years after Ampere's ingenious guess.
Already in the VI century. BC. in China, it was known that some ores have the ability to attract each other and to attract iron objects. Pieces of such ores were found near the city of Magnesia in Asia Minor, which is why they received the name magnets.
How do the magnet and iron objects interact? Let's remember why electrified bodies are attracted? Because near an electric charge, a peculiar form of matter is formed - an electric field. A similar form of matter exists around the magnet, but it has a different nature of origin (after all, the ore is electrically neutral), it is called magnetic field.
Straight or horseshoe magnets are used to study the magnetic field. Certain places of the magnet have the greatest attractive effect, they are called poles(north and south)... Like magnetic poles attract, while magnetic poles of the same name repel.
For the force characteristic of the magnetic field, use magnetic induction vector B... The magnetic field is graphically depicted using lines of force ( magnetic induction lines). Lines are closed, have no beginning or end. The place from which they emerge magnetic lines- North Pole (North), magnetic lines enter the South Pole (South).
The magnetic field can be made "visible" with iron filings.
Magnetic field of a conductor with current
And now about what they found Hans Christian Oersted and André Marie Ampere in 1820. It turns out that a magnetic field exists not only around a magnet, but also around any conductor with current. Any wire, for example, a cord from a lamp, through which an electric current flows, is a magnet! A wire with a current interacts with a magnet (try bringing a compass to it), two wires with a current interact with each other.
Forward current magnetic field lines are circles around a conductor.
Direction of the magnetic induction vector
The direction of the magnetic field at a given point can be defined as the direction that indicates the north pole of a compass needle placed at that point.
The direction of the lines of magnetic induction depends on the direction of the current in the conductor.
The direction of the induction vector is determined by the rule gimbal or rule right hand.
Vector of magnetic induction
This is a vector quantity that characterizes the force action of the field.
Magnetic induction of an infinite rectilinear conductor with a current at a distance r from it:
Magnetic field induction at the center of a thin circular turn of radius r:
Magnetic field induction solenoid(a coil, the turns of which are sequentially bypassed by current in one direction):
Superposition principle
If the magnetic field at a given point in space is created by several sources of the field, then the magnetic induction is the vector sum of the inductions of each of the fields separately
The Earth is not only a large negative charge and a source of an electric field, but at the same time the magnetic field of our planet is similar to the field of a gigantic direct magnet.
Geographic South is close to Magnetic North, and Geographic North is close to Magnetic South. If the compass is placed in the earth's magnetic field, then its north arrow is oriented along the lines of magnetic induction in the direction of the south magnetic pole, that is, it will show us where the geographical north is.
Characteristic elements terrestrial magnetism change very slowly over time - secular changes... However, from time to time magnetic storms when the Earth's magnetic field is strongly distorted for several hours, and then gradually returns to its previous values. This dramatic change affects the well-being of people.
The Earth's magnetic field is a "shield" that protects our planet from particles penetrating from space ("solar wind"). Near the magnetic poles, particle flows come much closer to the Earth's surface. With powerful solar flares the magnetosphere is deformed, and these particles can migrate to the upper atmosphere, where they collide with gas molecules to form aurora.
Iron dioxide particles on a magnetic tape are well magnetized during the recording process.
Magnetic levitation trains glide over the surface with absolutely no friction. The train is capable of speeds up to 650 km / h.
The work of the brain, the pulsation of the heart is accompanied by electrical impulses. In this case, a weak magnetic field arises in the organs.