department of physics vs physics department

department of physics and physics department both are nouns.

Word	Noun	Adjective	Verb	Adverb
department of physics	Yes	No	No	No
physics department	Yes	No	No	No

As nouns, department of physics and physics department are synonyms defined as:

department of physics and physics department: the academic department responsible for teaching and research in physics

department of physics (noun)	physics department (noun)
the academic department responsible for teaching and research in physics	the academic department responsible for teaching and research in physics