The answer is Atomic Physics. Atomic physics is the study of atomic interractions.
it is the branch of physics that deals with the structure and the behaviour of an atom is called atomic physics
Roughly speaking, in physics you learn how our Universe, the world we live in, works.
It means, physics of the nucleus - meaning the atomic nucleus.
Atom has got a hard material packed at its centre, called nucleus. Its dimension is some 10,000 times smaller than that of the atom itself. If the branch of physics, deals with the nucleus and its constituents such as proton and neutron, then that branch is called as nuclear physics. In case of atomic physics, another branch in physics, which deals only with the electrons going around the nucleus of the atom. Their energy and the radiation produced due to the transition of electrons in various energy levels are dealt with in this branch atomic physics.
Everything
thermodynamics,mechanics,optics,electricity,atomic physics etc.
Physics. More specifically sub-atomic physics
I suppose that physics is more important.
Nuclear Physics
If they don't learn physics they will vomit at the plane.
Microphysics is a difficult field of physics to learn.