Question

a proper real life phenomena related to atomic physics

Answer 1

Theoretical physics is the study of models of reality. Anything that happens can have a model built of it using the techniques of theoretical physics.

Experimental physics is the study of measurements of reality. Anything that happens can be measured using the techniques of experimental physics.

‘Branches’ of physics are something between an abstraction and a fiction. They are necessary in order to group the work into sensible groups, because nobody can know everything, but they aren’t real - I work in semiconductors, but I read books and papers about everything from soap to crystals for work purposes.