Hi Deepika,

Yes there is an entrace exam for Lateral entry. You can get the syllabus for exam from TU website. Most of the questions are related to that topics only. You can prepare your core subjects from any book having MCQs. I prepared from S. Chand publisher book and their were many questions in the exam from that. You can prepare from any other book also which is for Lateral entry exam. PCM questions were not tough at all, so just prepare your core subjects well. Good luck.

For other details you can check here:

http://thapar.edu/images/admission17/ADMISSION%20IN%20SECOND%20YEAR%20OF%20UG%20PROGRAM%20LEET.pdf