how do induction cookers work? I mean principle of work?

Answer 1

Mostly through eddy currents and magnetic hysterisis. Wiki has a good article on the link below.

Answer 2

Induction cookers require pots made of iron, which isn't all that good an electrical conductor; not copper or aluminium, which conduct better. They've got coils which conduct a current with a frequency of about 30 kHz. This produces currents in the iron saucepans which get hot because of resistance heating. I once worked in a foundry which used furnaces based on the same principle. You put all this ferrous metal scrap in the furnace and the alternating magnetic field caused the metal to melt.