The magnetic field is a special kind of matter that cannot be touch, see, hear, or taste. Can only detect it by the action of the electric current. It with some force will move the conductor made in this field. To find the module of the vector of magnetic induction, it is necessary to know three related quantities: the magnitude of the force (F) with which the magnetic field acts on in perpendicular to a magnetic line current-carrying conductor; the length (l) of the conductor; the current strength (I) in the conductor. First, multiply the amperage for length of conductor: I*l. Then divide the force value to the final product: F/(I*l). Example 1. May need to find the module of magnetic induction if the current in the conductor length of 0.25 meters, equal to 0.1 amps. And the strength of the magnetic field acting on the conductor is equal to 0.2 Newton. Solution: a=F/(I*l)=0.2 N/(0.1*0.25 m)=8Тл.
A clear picture of the magnetic field can be obtained to build the so-called lines of magnetic induction (closed directed curves that characterize the field). If the conductor is straight, the magnetic field covers him, defining the direction of these lines is subject to the following actions: imagine that you spin the screw around the conductor in the right direction, so that the tip of the screw is in the direction of the current in the conductor. That's a fictional rotation of the screw and directed lines of magnetic induction, and every single vector will be directed in the same direction but at a tangent to these lines.
If the conductor is a coil (solenoid), the magnetic field lines enter one side of the coil and out the other side. To determine the direction of magnetic induction vector, first determine the direction of magnetic field lines: to do this, grasp (mentally) conductor with the right hand so that four fingers showed the rotation of the current in the coil, and set aside on a ninety-degree thumb will show which direction is the magnetic field of the coil. Tangent to these lines at any point you will find the magnetic induction vector.