DIAS Physics Optional Notes by D.P. Vajpayee (B.Tech IIT Bombay, M.Phil JNU) — complete 8-volume, 1,552-page set covering the full UPSC CSE & IFoS Mains Physics Optional syllabus. First-principles derivations, solved illustrations, exam-calibrated problem sets. Digital edition, instant download. For UPSC/IFoS 2027 & 2028 aspirants.