The strength of the ampere characterizes the magnetic field. A magnetic field

Toddlers spend at school most their active childhood. And if for some only “homework” in mathematics causes difficulties, then for others the school becomes synonymous with problems, bad mood and all kinds of suffering. A lot can be the reason for a spoiled impression of the first education: undeveloped relationships with classmates or teachers, poor academic performance ... What should you do if you understand that your child has encountered problems that have turned school attendance into torture?

Problem: The child is too worried about bad grades.

Your son or daughter comes home from school in tears, to the question “what happened?” does not answer, hides his eyes, refuses to show the diary ... As a result, it turns out that such behavior is due to the fact that he got a two (or three) at school. And this happens every time the teacher puts a mark below the "five".

What to do:
Almost certainly, such a deep upset of a child with a bad assessment is closely related to the expectations that you yourself verbally or non-verbally broadcast. Some parents directly say “you should study for one five”, others hint - “if only your diary was as beautiful as that of your friend Petya”. In both cases, the child feels obliged to study "excellently", especially if such veiled or not very phrases slip through your speech often. And being an excellent student is not possible for everyone and not always.

So the first thing you need to do to help your child worry less about bad grades is to stop focusing on them. Praise your child for his achievements - for example, for how beautiful his handwriting has become, how quickly he solved a math problem, with what expression he read a poem, and not for fives. You must broadcast that good grades are great, but the main thing is real knowledge, and even more importantly, interest in learning and the efforts made. Only for this you need to believe in it yourself.

Problem: the child is offended by classmates

The sad reality is that in almost every modern classroom there is his "outcast". They offend him, they laugh at him, they do not give him a passage both directly and in figuratively. Often the reason for ridicule and mockery of classmates is some kind of "feature" of the child, which distinguishes him from the rest. Too tall, overweight, dresses differently, has a different eye shape or skin color, studies too well or too poorly, doesn't eat meat - anything can be the cause of bullying.

What to do:
Don't interfere "directly". If you decide to "have a conversation" with children who are abusing your son or daughter, you will only make the situation worse. Because you can’t physically be around all the time while your child is at school, and as soon as you leave, they will tease him also because “mommy stands up for him.”

Giving advice and lecturing a child on what to do in such a situation is also not effective. Because we give advice from an “adult” position - if a child had our confidence, knowledge and strength, perhaps he would not have any problems.

In this situation, you can only do one thing - to provide maximum support to the child. Listen to him when he wants to complain, tell him how much you love him. And try to find for him a society like him, where his peculiarity will be appreciated, and not rejected. If the child talks too much and grimaces - give him to the theater, if he is too tall for his age - to the basketball section. Seeing that he is not the only one, the child will become less embarrassed by his “feature”, and quite likely he will begin to be proud of her, and other people's ridicule will no longer offend him. And as soon as the gun does not reach the target, it stops firing.

If the situation only worsens over time and comes to physical assault, you may need to consider transferring your child to another school. Extra half an hour of the road or not high rating on individual items- not as scary as the destroyed psyche of a child.

Problem: Child has no friends at school

Relationship problems at school are not always related to the fact that someone offends the child - sometimes they simply ignore him. If classmates do this on purpose, it’s worth “fighting” in the same ways as with active “arrivals”, but most often the child’s lack of friends at school is still associated with his natural modesty. Often this problem is faced by children who have moved into new school, where their teams and circles of interest have already formed. And, if for an active and lively child to join a new environment is not a problem, then a shy child will stand on the sidelines, not daring to approach and talk to a new company.

What to do:
First, make sure that the desire to have friends belongs to your child, not to you. Most children feel the need to belong to a group, but there are exceptions to every rule - your child may be one of them. If your little schoolboy really wants to make friends with someone, but cannot, help him - arrange some kind of fun event to which you invite other children.
Outside of school, in situations where they find it interesting and enjoyable, children are usually more approachable - and will not mind playing with your son or daughter.

If you have no time to organize picnics and hikes, try to invite the parents of one of your classmates to visit. After all, it doesn't hurt to make friends in the school environment too. Ask your new acquaintances to take their child to visit so that yours is not bored. And be sure to come up with some kind of bonding fun activity that the kids can do together - building a new construction set, building a pillow fort, combing a dog, anything they can do together.

Problem: overloaded schedule, the child gets tired and cannot cope with the load

Teachers complain that your child sleeps in class. At home, he refuses not only to help around the house - but also to play, because he is too tired and wants to rest. Or maybe he doesn’t have time for games at all, because after school he needs to not only do his homework, but also go to a riding lesson, and then work out with a Spanish teacher ...

What to do:
Moderate your parental ambitions - almost always, when a child is on the verge of a nervous breakdown due to overwork, it turns out that, in addition to school, he attends several other different circles and sports sections. Taking care of the all-round development of the child is good and right, but exactly as long as his physical and mental health.

Try giving up, at least temporarily, piano lessons and not taking your son or daughter to a private chess teacher three times a week. Observe the child: has he become more cheerful, cheerful, active? If not, he may need more time to recover. Also, it will not be superfluous to check whether overwork and nervous exhaustion are caused by a lack of vitamins in the body.

If, in addition to school, the child does not have additional loads, while teachers still complain about his inattention, perhaps you should check the child for attention deficit disorder. With ADHD (as the syndrome is abbreviated), due to neurological features the child has difficulty concentrating on something, cannot hold attention for a long time, which affects school performance. Children with this syndrome need special help in assimilation of information.

Problem: the teacher dislikes the child for some reason and unreasonably lowers the grades

In an ideal world, teachers should be impartial, assessing the true level of knowledge of the child, not paying attention to their personal likes and dislikes. But in reality, alas, quite the opposite often happens. And the teacher chooses his "favorites" and "boys (girls) to beat." Moreover, it is far from always that children who are famous for bad behavior or do not know the subject fall into the “unloved ones”. It’s just that, for example, a teacher loves active guys who always stretch out their hand and strive to answer any of her questions, and those who sit quietly (perhaps because, due to their temperament, do not seek to “climb forward”) by default put “one step lower ".

What to do:
First, try to "scout the situation." Talk to the parents of other children - how does this teacher feel about them? Are they complaining about her? Perhaps, for a particular teacher, something globally goes wrong in life, and he “breaks down” on the children. In this case, you should contact the director and solve the problem administratively - change the teacher for the whole class.

If your guess that the teacher does not like your child specifically is confirmed, try talking openly with her. The main thing is not to start with threats or negativity. It will be much better for you and your child if you manage to resolve the conflict peacefully. Ask what Vasya needs to do to improve his grades? Say that you feel that your son "does not pull" her subject - what could she advise to improve the situation? Tell us about the features of your child - maybe, realizing that he does not pull his hand, not because he does not know anything, but because he is phlegmatic by temperament, she will begin to ask him more often - and make sure that he knows everything better than many.

If, despite all your conversations, the teacher will not leave your child alone, use this case as an example, telling the child that this happens in life - even if we try very hard and do everything well, others do not always adequately evaluate it . Praise the child and say that you are sure that he knows mathematics (literature, English) better than many, and if the grades do not reflect this knowledge, it is not his fault.

In general, when a child complains to you about something that happens at school (and not only there), try to hear not only words, but also emotions. Listen to everything your baby has to say to you, and voice the feelings you think he is experiencing. “I think you are very upset” - and shut up. The child himself will let you know whether you “guessed” correctly or not, and most importantly, he will receive “permission” to express everything that has accumulated in his soul. Such deep emotional contact is the best thing you can give your child in the presence of a problem of any nature.

And you can often remind him that he is wonderful and you love him, and school is just one of the stages of a long, long life. Former offenders and harmful teachers will remain in the past, and he will definitely meet those who will appreciate all his wonderful qualities.

Photo - photobank Lori

Practical advice: how to alleviate the condition of a child with fever and what to do if seizures occur.

Fever is considered to be an increase in body temperature above upper limit its normal fluctuations during the day. Depending on the body temperature of the child, three degrees of fever are distinguished:
Subfebrile - 37.2-38.0 ° С
Febrile - 38.1-39.0 ° С
Hyperthermic - 39.1 ° C and above.

Normal temperatures

A temperature of 37 degrees is not "normal" for everyone, as we have been told for many years. This is simply not true. The established “norm” is very conditional, since an indicator of 37 degrees is an average value. Many people have a normal temperature higher or lower. This is especially true for children. Studies have shown that the body temperature in most absolutely healthy children ranges from 35.9–37.5 degrees and only in a few is exactly 37 degrees.
Fluctuations in a child's body temperature during the day can be significant: in the evening it is a whole degree higher than in the morning. Finding a child with a slightly elevated temperature in the afternoon, do not worry. For this time of day, this is quite normal.
The temperature may rise for reasons unrelated to any disease: when digesting a rich and heavy meal, or at the time of ovulation in teenage girls during their puberty. Sometimes the rise in temperature is side effect medicines prescribed by a doctor - antihistamines and other drugs.

How to care for a child with a high fever

Children with fever should be lightly dressed and in a well-ventilated, draft-free room. Infants are especially characterized by the dependence of body temperature on temperature. environment because their body is just learning to regulate its temperature. If the child is wrapped up, undress him and cover him with a thin diaper.
If the temperature is above 38°C, you can bathe your baby in a bath that is only (!) 1°C lower than his baby's temperature (this would be a hot to the touch bath for a person with a normal temperature!). It is possible to bathe together and breastfeed at the same time.
High fever and the symptoms that usually accompany it lead to significant fluid loss and cause dehydration. If the child refuses to eat, do not forget to give him water. Let it be your favorite, but healthy drinks. Children who are on breastfeeding, enough breast milk, they should be given free access to their mother's breasts.
At a high temperature, let the baby rest, do not wake him up, even if the body temperature is above 380C. Sleep is an excellent medicine.
In older children, diaphoretics can be used. As a rule, it is raspberries or natural dark honey, linden decoction. Before giving something diaphoretic, the child should gradually drink at least 100-300 ml of liquid. Dried fruit compote is best. Only after 15-20 minutes you can give raspberries a drink. When it begins to act, the previously drunk liquid “leaves” the body. If the child did not drink anything, raspberries will lead to even greater dehydration of the body, and already deficient moisture will be “squeezed out” of it.
Then the child, dressed in cotton, should be left under a light sheet. Sweat does not need to be wiped off - evaporating, it cools the skin. After the main sweating has passed, the child needs to be changed and put to bed.
It should also be remembered that experienced pediatricians pay more attention to the "general condition of the child" than to thermometer readings. Can't comfort a child? Is he lethargic and indifferent? Can't he drink? Here are the top warning signs of something more serious that may be happening to the child. As for fever, within certain limits, it is only a "normal and healthy response" child's body for an infection.

Caution: rubdown

Sponging the body with cool water reduces the temperature only for the very period of sponging (there are scientific work showing this). In addition, the procedure is very unpleasant for a person whose temperature has not yet reached its maximum, that is, it is in the rising stage.
Here are a few reasons why rubdowns are not recommended for lowering body temperature:
lack of evidence of persistent temperature reduction in children;
rubbing leads to spasm of skin vessels, which further complicates heat transfer;
rubbing can cause shivering, therefore, increase the metabolic rate, which will lead to a further rise in temperature.

What to do if seizures occur

Children under the age of five are usually prone to febrile seizures. Children who have experienced such convulsions at this age rarely suffer from them later.
There are large-scale studies, presented in a 2003 WHO Bulletin, showing that antipyretics do not prevent seizures in children who have previously had episodes of febrile seizures. However, if seizures occur, a pediatrician's consultation is necessary!
A study of 1706 children who experienced febrile seizures found no cases of motor impairment and did not record deaths. There is also no convincing evidence that such seizures increase the risk of epilepsy later on.
High fever does not in itself cause seizures. They are caused only by a sharp rise in temperature. Many parents are afraid of high fever in their children, because they have noticed that it is accompanied by seizures. They can be understood: a child in convulsions is an unbearable sight. Those who have observed this may find it difficult to believe that, as a rule, this condition is not serious. In addition, it is relatively rare - only 4 percent of children with high temperature convulsions are observed, and there is no evidence that they leave serious consequences.
If your child has a fever-related seizure, try not to panic. Of course, giving advice is much easier than following it. The sight of a child experiencing convulsions is truly frightening. Still: Remind yourself that seizures are not life-threatening or permanently damaging for your baby, and take simple steps to ensure your child doesn't get hurt during a seizure.
Do not try to give fever-reducing medicine to a child with seizures!
First of all, turn the child on its side so that it does not choke on saliva. Then make sure that there are no hard and sharp objects near his head that he can get hurt during an attack.
After that, for your own peace of mind, you can call the doctor and tell him what happened.
Most seizures last a few minutes. If they persist, call your doctor immediately. If, after an attack of convulsions, the child does not fall asleep, it is impossible to give him food and drink for an hour. Due to severe drowsiness, he may choke.
Lavrishcheva Julia, pediatrician, homeopath. Tazherova Anna, pediatrician

Magnetic induction. Lorentz force. The magnetic field is one of the two components of the electrical magnetic field(see section 3.2). The magnetic field acts on moving particles, currents and magnetic moments. The sources of the magnetic field are moving particles, currents, magnetic moments and alternating electric fields. A characteristic of the magnetic field is the magnetic induction vector B. To determine B, you can use the expression for the force acting on a charged particle in an electromagnetic field:

where c cm/s is the electrodynamic constant, equal to speed light in a vacuum. The force exerted on a particle by a magnetic field is called the Lorentz force.

To determine the magnetic induction B using formula (51), it is necessary:

1) measure the force acting on a stationary particle to separate the action electric field;

2) find the direction of velocity for which at constant value magnetic force is maximum;

3) by the magnitude of the force, find the modulus of magnetic induction:

4) in the direction of Rtlx and find the direction Y using the gimlet rule.

Magnetic induction is also conveniently determined by the torque with which the magnetic field acts on a small coil with current. Only a magnetic field acts on a coil with current.

In SI, magnetic induction is measured in tesla in CGS - in gauss

Example 1. Let us consider the motion of a non-relativistic particle with mass and charge in a uniform magnetic field with induction. Let at some time the particle velocity be directed at an angle a to the Lorentz force is perpendicular to both k (i.e., and B (i.e., the velocity projections are preserved) and on the direction of the induction vector and on the plane perpendicular to it). perpendicular plane the particle moves along a circle, the radius of which can be found from Newton's second law: The period of rotation does not depend on speed. The resulting movement occurs in a spiral with a radius R with a step

Ampere's law. The force acting on a current element in a magnetic field is equal to the sum of the Lorentz forces acting on moving free charges:

When deriving the Ampère force acting on a volume element with a current density and on line element used with current

current connection with average speed free charges(40). To calculate the total force acting on a volume with a distributed current or on an extended section of a wire with current, it is necessary to perform integration. For example, a force acts on a straight section of a wire with a current I in a uniform magnetic field with induction B A force acting in a uniform field on any closed loop with current is equal to zero:

Magnetic moment of a circuit with current. magnetic moment circuit with current is called a vector quantity equal to

where the integration is carried out over any surface stretched over the contour, and the direction of the normal is determined by the direction of movement of the gimlet when it rotates in the current. In the case of a flat contour

The magnetic moment of the circuit, as well as the dipole moment of the electric dipole (see Sections 3.1 and 3.3), determines the magnetic field of the circuit at large distances away from it and describes the behavior of a small current-carrying coil in a magnetic field.

Example 2. Consider a rectangular circuit whose side lengths are equal to a and suspended from side a in a uniform vertical magnetic field with induction B (Fig. 36). When the current is turned on with force I, the circuit will deviate by an angle (3), at which the moment of gravity is balanced by the moment of Ampere forces or Note that the torque acting on the circuit from the magnetic field is equal to A similar expression was obtained for torque acting on an electric dipole in an electric field (see Section 3.3).

Basic Laws of Dynamics. Newton's laws - first, second, third. Galileo's principle of relativity. The law of universal gravitation. Gravity. Forces of elasticity. The weight. Friction forces - rest, sliding, rolling + friction in liquids and gases.

Kinematics. Basic concepts. Uniform rectilinear motion. Uniform movement. Uniform circular motion. Reference system. Trajectory, displacement, path, equation of motion, speed, acceleration, relationship between linear and angular velocity.

simple mechanisms. Lever (lever of the first kind and lever of the second kind). Block (fixed block and movable block). Inclined plane. Hydraulic Press. The golden rule of mechanics

Conservation laws in mechanics. Mechanical work, power, energy, law of conservation of momentum, law of conservation of energy, equilibrium of solids

Circular movement. Equation of motion in a circle. Angular velocity. Normal = centripetal acceleration. Period, frequency of circulation (rotation). Relationship between linear and angular velocity

Mechanical vibrations. Free and forced vibrations. Harmonic vibrations. Elastic oscillations. Mathematical pendulum. Energy transformations during harmonic vibrations

mechanical waves. Velocity and wavelength. Traveling wave equation. Wave phenomena (diffraction, interference...)

Hydromechanics and Aeromechanics. Pressure, hydrostatic pressure. Pascal's law. Basic equation of hydrostatics. Communicating vessels. Law of Archimedes. Sailing conditions tel. Fluid flow. Bernoulli's law. Torricelli formula

Molecular physics. Basic provisions of the ICT. Basic concepts and formulas. Properties of an ideal gas. Basic equation of the MKT. Temperature. The equation of state for an ideal gas. Mendeleev-Klaiperon equation. Gas laws - isotherm, isobar, isochore

Wave optics. Corpuscular-wave theory of light. Wave properties of light. dispersion of light. Light interference. Huygens-Fresnel principle. Diffraction of light. Light polarization

Thermodynamics. Internal energy. Job. Quantity of heat. Thermal phenomena. First law of thermodynamics. Application of the first law of thermodynamics to various processes. Heat balance equation. The second law of thermodynamics. Heat engines

Electrostatics. Basic concepts. Electric charge. The law of conservation of electric charge. Coulomb's law. The principle of superposition. The theory of close action. Electric field potential. Capacitor.

Constant electric current. Ohm's law for a circuit section. Operation and DC power. Joule-Lenz law. Ohm's law for a complete circuit. Faraday's law of electrolysis. Electrical circuits - serial and parallel connection. Kirchhoff's rules.

Electromagnetic vibrations. Free and forced electromagnetic oscillations. Oscillatory circuit. Alternating electric current. Capacitor in AC circuit. An inductor ("solenoid") in an alternating current circuit.

Electromagnetic waves. The concept of an electromagnetic wave. Properties of electromagnetic waves. wave phenomena

You are here now: A magnetic field. Magnetic induction vector. The gimlet rule. Ampere's law and Ampere's force. Lorentz force. Left hand rule. Electromagnetic induction, magnetic flux, Lenz's rule, law electromagnetic induction, self-induction, magnetic field energy

The quantum physics. Planck's hypothesis. The phenomenon of the photoelectric effect. Einstein's equation. Photons. Bohr's quantum postulates.

Elements of the theory of relativity. Postulates of the theory of relativity. Relativity of simultaneity, distances, time intervals. Relativistic law of addition of velocities. The dependence of mass on speed. The basic law of relativistic dynamics...

Errors of direct and indirect measurements. Absolute, relative error. Systematic and random errors. Standard deviation (error). Table for determining the errors of indirect measurements of various functions.

A magnetic field:

Inhomogeneous and uniform magnetic field. The force with which the field of a bar magnet acts on a magnetic needle placed in this field, in different points field can be different both in modulus and in direction. Such a field is called inhomogeneous. The lines of an inhomogeneous magnetic field are curved, their density varies from point to point. In a certain limited region of space, it is possible to create a uniform magnetic field, i.e. field, at any point of which the force on the magnetic needle is the same in magnitude and direction. For the image of the magnetic field, the following method is used. If the lines of a uniform magnetic field are located perpendicular to the plane of the drawing and are welded from us behind the drawing, then they are depicted with crosses, and if because of the drawing towards us, then with dots.

A magnetic field- a force field acting on moving electric charges and on bodies with a magnetic moment, regardless of the state of their movement; magnetic component of the electromagnetic field.

The main power characteristic of the magnetic field is magnetic induction vector

The magnetic field of macrocurrents is described by the intensity vector H. (B= 0 H).

Magnetic induction:

Magnetic induction-vector quantity, which is a force characteristic of the magnetic field (its action on charged particles) at a given point in space. Determines the force with which the magnetic field acts on a charge moving at speed.

Units of measurement: Tl.

The module of the magnetic induction vector B is equal to the ratio of the module of the force F, with which the magnetic field acts on a current-carrying conductor located perpendicular to the magnetic lines, to the current strength in the conductor I and the length of the conductor l.

Magnetic induction does not depend on the strength of the current or on the length of the conductor, it depends only on the magnetic field. That is, if we, for example, reduce the current strength in the conductor without changing anything else, then it will not decrease the induction, with which the current strength is directly proportional, but the force of the magnetic field on the conductor. The magnitude of the induction will remain constant. In this regard, induction can be considered a quantitative characteristic of the magnetic field.

Magnetic induction has a direction. Graphically, it can be drawn as lines. The lines of induction of the magnetic field are what we have so far called in earlier topics magnetic lines or magnetic field lines. Since we have derived the definition of magnetic induction above, we can define and lines of magnetic induction.

Lines of magnetic induction are lines, the tangents to which at each point of the field coincide with the direction of the magnetic induction vector.

In a uniform magnetic field, the lines of magnetic induction are parallel, and the magnetic induction vector will be directed in the same way at all points.

In the case of a non-uniform magnetic field, the magnetic induction vector will change at each point in space around the conductor, and tangents to this vector will create concentric circles around the conductor.

The direction of the lines of magnetic induction is determined by the gimlet rule.

Ampere's law:

Ampère's law shows the force with which a magnetic field acts on a conductor placed in it. This force is also called by the power of Ampere.

The wording of the law: the force acting on a conductor with current placed in a uniform magnetic field is proportional to the length of the conductor, the magnetic induction vector, the current strength and the sine of the angle between the magnetic induction vector and the conductor.

If the size of the conductor is arbitrary, and the field is not uniform, then the formula is as follows:

The direction of Ampère's force is determined by the rule of the left hand.

left hand rule : if arranged left hand so that the perpendicular component of the magnetic induction vector enters the palm, and four fingers are extended in the direction of the current in the conductor, then set aside by 90° thumb, will indicate the direction of Ampere's force.