Magnet , around for ferrite and SmCo, about for NIB and lower for flexible ceramics, but the exact numbers depend on the grade of material. An electromagnet, in its simplest form, is a wire that has been coiled into one or more loops, known as a solenoid. When electric current flows through the wire, a magnetic field is generated. It is concentrated near (and especially inside) the coil, and its field lines are very similar to those of a magnet. The orientation of this effective magnet is determined by the right hand rule. The magnetic moment and the magnetic field of
Magnetic field the area times the magnetic field normal to that area. (This definition of magnetic flux is why is often referred to as "magnetic flux density".) The negative sign represents the fact that any current generated by a changing magnetic field in a coil produces a magnetic field that "opposes" the "change" in the magnetic field that induced it. This phenomenon is known as Lenz's law. This integral formulation of Faraday's law can be converted into a differential form, which applies under slightly different conditions. This form is covered as one of Maxwell's equations below. Similar to the way that a