R Delhi Babu
Magnetohydrodynamics describes the dynamics of a fluid that interacts with a magnetic field. This subject is of prime importance in missile and spacecraft dynamics, propulsion communications, and power generators. Hydromagnetic flows occur in astrophysics and geo-physics also. There are some characteristic lengths of considerable importance in MHD. They are Debye characteristics length and Larmor radius - the radius of the path of a charged particle moving in a magnetic field and transverse to the field lines. Larmor radius is also known as gyro radius and cyclotron radius. These quantities are useful for the description of MHD phenomena in magnetohydrodynamics. The basic concept in electromagnetism is Coulomb’s law for the force on a charged particle, in an electrical field. Coulomb’s law states that 'The force on a charged particle is proportional to the product of the charge and the local electrical field seen by the particle'. When a charged particle moves in the presence of an arbitrary electric and magnetic field, the resulting force is called the Lorentz force.