Atoms or ions with unpaired electrons are attracted to a magnetic field; the more unpaired electrons, the greater is the attraction. Such substances are called paramagnetic. Molecular oxygen is a paramagnetic gas by virtue of its two unpaired electrons.
In nuclear power plant the graphite is used as a moderator. The job of the moderator is to absorb some of the kinetic energy of the neutrons to slow them down. This is because slow neutrons are more easily absorbed by uranium-235. A neutron slowed In this way can start the fission process.
A DC motor can be operated from a single-phase AC supply.
The direction of the torque produced by a DC machine is determined by the direction of current flow in the armature conductors and by the polarity of the field.
Torque is developed in a DC machine because the commutator arrangement permits the field and armature currents to remain in phase, thus producing torque in a constant direction.
A similar result can be obtained by using an AC supply, and by connecting the armature and field windings in series.