i am unable to understand this topic. i had just gone in 12th.please tell any reference book, my physics is weak

Dear Abhishek,

First of all you need to mention the topics of Physics that you are not cleared, as far as books are concerned you need to clear first of all basics of your subject through " Kumar Mittal" . This book is very precise and explains each and every concept very broadly and clearly.

After you are done with your basics and then if you need to go for some higher level studies then you can go for " H.C.Verma"

or "New patterns of IIT JEE Physics" of arihant pulications.

Even askiitians also provide their study material.

For detail you visit the following link:

http://www.askiitians.com/iit-study-material/

Thanks and regards

Akhilesh Shukla