How can you reverse the poles of an electromagnet?
The strength of the magnetic field between the poles of an electromagnet would be unchanged if :
(a) current in the electromagnet winding were doubled
(b) direction of current in electromagnet winding were reversed
(c) distance between the poles of electromagnet were doubled
(d) material of the core of electromagnet were changed
A bar magnet has no markings to indicate its poles. How can you find out the location of the north pole?