Hello there

See, each and every chapter is important is important in JEE syllabus.And the chapter you mentioned is Heat and Thermodynamics is one of the most important topics including

sound and waves , electricity,magnetism etc..

Candidates most often think Heat and Thermodynamics as toughest part but with practice and understanding it will be clear .

According to JEE MAIN 2021 ,these are the most important topics and chapters of Physics  ;

*THERMODYNAMICS

*ELECTROSTATICS

*ROTATIONAL MOTION

*SHM

*MAGNETISM

*MODERN PHYSICS

*OPTICS

Here are some book recommendations ,you can follow ;

•NCERT CLASS 11 AND 12 TEXTBOOKS

•CONCEPTS OF PHYSICS BY HC VERMA (BOTH THE VOLUME)

•PROBLEMS IN GENERAL PHYSICS BY I.E IRODOV

•FUNDAMENTALS OF PHYSICS BY HALLIDAY,RESNICK & WALKER

You can also visit the link for preperation tips ;

https://engineering.careers360.com/articles/jee-main-preparation-tips-expert

In JEE every topic is important. so to ensure the best results you shouldn't treat any topic entirely ignored. Now Heat & Thermodynamics is one of the chapters which have high weightage in JEE MAINS. Around 12 marks is asked alone in average from Thermodynamics every year. So dont miss it.

The Important parts in Thermodynamics are the Efficiency of Engines, Entropy, Refrigeration.

To know more about chapterwise weightage visit the link below:

https://engineering.careers360.com/articles/jee-main-syllabus-weightage

To know more about Thermodynamics and for some useful tips visit the link below:

https://learn.careers360.com/physics/thermodynamics-chapter/

some of the classic books you follow:

• concepts of physics by HC VERMA
• Principles of Physics Haliday, Resnick, Walker
• Thermodynamics by DC PANDEY

I hope this answer helps. All the very best for your future endeavors!