What is magnetic field induction? To answer this question, recall the basics of electrodynamics. As is known, a motionless charge carrier q located in the electric field is biased with force F. The larger the charge (regardless of its properties), the greater the force. This is tension - one of the properties of the field. If we designate it as E, then we get:
E = F / q
In turn, fields of a magnetic nature influence mobile charges. However, in this case, the force depends not only on the magnitude of the electric charge, but also on the direction vector of movement (or, more precisely, speed).
How can we study the configuration of the magnetic field? This problem was successfully solved by well-known scientists - Ampere and Oersted. They placed a conducting circuit with electric current in the field and studied the intensity of the effect. It turned out that the result was influenced by the orientation of the contour in space, which indicated the presence of the direction vector of the moment of forces. Induction of a magnetic field (measured in Tesla) is expressed through the ratio of the mentioned moment of force to the product of the area of the conductor of the circuit and the flowing electric current. In fact, it characterizes the field itself, which is necessary in this case. We express everything said through a simple formula:
B = M / (S * I);
where M is the maximum value of the moment of forces, depends on the orientation of the contour in a magnetic field; S is the total area of the contour; I is the current value in the conductor.
Since the induction of the magnetic field is a vector quantity, then it is required to find its orientation. The most visual representation of it is given by an ordinary compass, the arrow of which always points to the north pole. Induction of the magnetic field of the earth orients it according to magnetic lines of force. The same thing happens when the compass is placed near the conductor through which current flows.
Describing the contour, we should introduce the concept of magnetic moment. This is a vector numerically equal to the product of S by I. Its direction is perpendicular to the conditional plane of the conductive circuit itself. You can determine by the well-known rule of the right screw (or gimlet, that the same thing). The magnetic field induction in the vector representation coincides with the direction of the magnetic moment.
Thus, we can derive the formula for the force acting on the circuit (all quantities are vector!):
M = B * m;
where M is the total vector of the moment of force; B - magnetic induction; m is the value of the magnetic moment.
No less interesting is the induction of the magnetic field of the solenoid. It is a cylinder with a wound wire through which electric current flows. It is one of the most used elements in electrical engineering. In everyday life, every person encounters solenoids constantly, without even knowing about it. So, the magnetic field created by the current inside the cylinder is completely homogeneous, and its vector is directed coaxially with the cylinder. But outside the cylinder body, the magnetic induction vector is absent (equal to zero). However, the above is true only for an ideal solenoid with infinite length. In practice, however, the restriction makes its own adjustments. First of all, the induction vector is never equal to zero (the field is also recorded around the cylinder), and the internal configuration also loses its homogeneity. Why then do we need a “perfect model”? Very simple! If the cylinder diameter is less than the length (as a rule, it is), then in the center of the solenoid the induction vector practically coincides with this characteristic of the ideal model. Knowing the diameter and length of the cylinder, we can calculate the difference between the induction of a finite solenoid and its ideal (infinite) counterpart. It is usually expressed as a percentage.