Which of the following describes a magnet that only has a field when a current is present? permanent magnet magnetic domain electromagnet magnetic pole

The answer to your question is "eelectromagnet". Electromagnets only produce a magnetic field when they have an electric current nearby, and are some of the more powerful magnets on Earth, running things such as MRI machines, and junkyard manet cranes. They also are part of why electric motors spin.

An  atom  (ours, not carroll's) consists of a positively charged  nucleus, surrounded by one or more negatively charged particles called  electrons. the positive charges equal the negative charges, so the atom has no overall charge; it is electrically neutral. most of an atom's mass is in its nucleus; the mass of an electron is only 1/1836 the mass of the lightest nucleus, that of hydrogen. although the nucleus is heavy, it is quite small compared with the overall size of an atom. the radius of a typical atom is around 0.1 to 0.25 nanometres (nm), whereas the radius of a nucleus is about 10-6  nm.  *  if an atom were enlarged to the size of the earth, its nucleus would be only 200 feet in diameter and could easily rest inside a small football stadium.read more on -