a) Any directionally moving charge, as well as a time-varying electric field, cause a magnetic field to appear in space.
b) The magnetic field can be detected using conductors with current, on which the field has an orienting effect.
c) There are no separate positive and negative magnetic charges in nature. No matter how small we make the pieces of the permanent magnet, we will always find the north and south poles.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.