In a vacuum, vph = c0 = 299,792,458 meters per second, a fundamental physical constant. The electromagnetic wave equation derives from Maxwell’s equations. In most older literature, B is called the magnetic flux density or magnetic induction.

So if you place a point charge inside a conducting shell the inner side of the conducting shell will have same amount but opposite charge distributed so that a Gaussian surface in side the conducting material have zero enclosed charge, which is required to make the electric field zero in the conducting material.

The charge per unit area of solid surface expressed in Coulomb/square meter.

Two definitions are possible: using pole strengths, using currents: a = pole separation. N is the number of turns of conductor.

Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. At high energy the weak force and electromagnetic force are unified as a single electroweak force.

The current density vector j is the vector whose magnitude is the electric current density, and whose direction is the same as the motion of the positive charges at M. For example, for charge carriers passing through an electrical conductor, the area is the cross-section of the conductor, at the section considered.

The magnitude of current density is also equivalent to the ratio of current (I) to area (A). In equation form, current density can be written as… The SI unit of current density is the ampère per square meter [A/m2]….Summary.