What are eddy currents ?

Explanation

Eddy currents: See Very Short Answer Type Question No. 12 (1 Mark) Experimental demonstratton of eddy currents: Introduce a soft iron core inside a solenoid and conmect it to a source of alternating emf Place a metallic disc over the cross-sectional face of the soft iron core as shown in Fig. below. As the cirenit is switched on, the metalltc disc is thrown up into the air.
When the circuit is switched on, the curent starts growing through the solenoid. As the current grows, the magnetic field lines along the axis of the solenoid and hence the magnetic flux through the dise also increases from zero to some finite value. Due to this, induced currents are produced in the disc and the disc is converted into a small magnet. If the upper face of the soft iron core acquires N-polarity initially, then lower face of the disc also acquires N-polarity in accordance with Lenz.s law. Due to repulsive force between the upper face of the soft iron core and the lower face of the disc, the latter is thrown up.
Disadvantages of eddy currents:
See Short Answer Type Question No. 8 (2 Marks)
Application of eddy current:
Electromagnetic damping: The oscillations of the coil of a galvanometer can also be stopped by short circuiting the two ends of the coil through a tapping key. When the key is pressed, the coil circuit is closed and the eddy curents are produced due to the motion of the coil in the magnetic field of the magnet of the galvanometer. Due to Lenz.s law, the direction of eddy currents is such that it opposes the oscillations of the coil.