CBSE Class 12-science Answered

 Moving a magnetic field with respect to an electric conductor induces an emf into the conductor. This situation exists inside a coil [solenoid] which is energized by an alternating current, [usually at hi-frequency]. If we place a metal core inside the solenoid, any motion of the magnetic field will induce an emf in the metal core. In [electromagnetic induction].. the direction of the magnetic lines of force .. the motion of the magnetic lines of force with respect to the electric conductor...and the flow of electric current.. are all at right angles to each other. As the current is increased in the solenoid, more magnetic lines of force are set up.  the crowding of more lines of force  cause the existing lines of force to be pushed outward [at rt.angles] along a radius from the axis of the solenoid.  The motion of these AC induced lines of force along the various radii of the solenoid is the cause of the induced emf inside the core material of the solenoid. To achieve this motion, the current must flow in a circle around the circumference of the metallic core. This Current is called [EDDY CURRENT].  Eddy current is produced in any core material that is an electric conductor.  the core does not have to be magnetic material..brass will work just as easily..The core will become very HOT due to eddy currents produced as a result of hi-frequency AC, in the solenoid. This heat comes from [I(square)R] power losses as the eddy current flows through the core material [resistance to change].  A usage for this is [Induction Heating]. The solenoid is energized with a hi-frequency AC current..and the work [core] to be heated is enclosed inside this solenoid..and it becomes very hot such as in Brazing..