Hey aspirant,

The following books are important for Physics optional  for  UPSC  Exam-

• A Dictionary of Physics-Goldstein
• Mechanics by JC Upadhyay.
• Thermodynamics by Garg, Bansal, Ghosh.
• Atomic Physics- J.B. Rajan
• Quantum Mechanics by David J. Griffiths.
• Atomic and Molecular Spectra by Raj Kum.
• Quantum Physics by HC Verma
• NCERT books from 6th-12th books
• Advanced Level Physics – Nelkon & Parker
• B.L Theraja (Vol 1) or Vincent Del Toro
• Classical Mechanism -Gupta, Kumar & Sharma – Takewale & Puranik -H.Goldstein
• Concept of Modern Physics – Arthur Beiser
• Electricity & Magnetism: D.C. TAyal, B.S. Agarwal, Griffith
• Electronics – Millman & Halkias, S. Ramnam, Ryder or Bolstead, Malvina
• Electronics -Allen Mottershead
• EM Theory -Chopra&Agarwal/Satya Prakash
• Fundamental of Magnetism electricity – B.N. Basudeva
• Mechanics – D.S. Mathur, B.S. Agarwal
• Mechanics – Kleppner & Kolenkow -D.S. Mathur
• Modern Physics – A Beiser (Concepts of modern physics), S.L. Gupta, B.S. Agarwal, J.B. Rajan
• Nuclear Physics – D.C. Tayal
• Nuclear Physics -S.B Patel
• Optics – Brijlal & Subramanyam, B.S. Agarwal, Ajoy & Ghatak
• Optics-Ajoy Ghatak-B.S. Agarwal
• Physics Vol I&II by David Halliday and Resnick
• Properties of Matter – B. Aggarwal
• Quantum Mechanics – A Ghatak
• Quantum Mechanics -Ghatak & Lokanathan
• Quantum Physics- Resnick & Eisberg
• Solid State Physics -Kittel
• Special Relativity-R.Resnick -Gupta & Goyal
• Statistical Physics -B.B laud
• Thermal Physics – P.K Chakraborty – Satya Prakash, Singhal & Agarwal
• Thermal Physics – Singal, Agarwal & Prakash, B.S. Agarwal, Shah & Srivastava
• University Physics – Zemansky
• Wave/Spl.Relatively – D.S. Mathur/Kleppner Kolenkow
• Waves and Oscillations – Brijlal & Subramanyam, B.S. Agarwal

You can refer to these books.

Hope this helps you .

If you have any doubts,you can ask in comments section

All the best.

UPSC Physics has approximately 17 topics to be covered and each topic has a better book writen by specific authors. Here we have mentioned 2 books per topic for you:

An Introduction to Mechanics by Kleppner and Kolenkow

Mechanics by D S Mathur

Theory of Relativity by Goyal and Gupta

Intriduction to Special Relativity by Robert Resnick

A Text Book of Optics by Brijlal and Subrahmanyam

Optics by Gahtak Ajoy

Electricity and Magnetism by Satya Prakash

Introduction to Electrodynamics by David J Griffiths

Quantum Physics by Resnick and Eisberg

Concepts of Modern Physics by Arthur Beiser

Quantum Mechanis by Mourdune Zettler

Quantum Mechanics by Lokanathan and Ajoy Ghatak

Atomic and Molecular Spectra by Rajkumar

Nuclear Physics by SB Patel

Solid State Physics by SO Pillai

Solid State Physics by Puri RK and VK Babbar

Electronics by BL Theraja