i am B.Sc[main subject physics],can i do B.tech after this?

You are not eligible for lateral entry admissions as applicable to Diploma candidates, Start afresh after qualifying state level/ national level eligibility test. A better alternative would be MSc/PhD track. Why do you need two degree qualifications with a three year lag?

You are now eligible in colleges under Anna University

Recently Anna University has started offering lateral entry admissions for B Sc

As per the revised scheme of some universities like Anna University, B Sc candidates are also eligible for lateral entry admission.

If you are Interested B.Tech then go for it, but why waste again 3 years. Instead opt for M.Sc or MBA.

HI,B.tech after r doing M.tech is best,but r want to change field,then u r doing MCA or MBA is best for u or your career.At a time mostly student r doing b.tech after MCA or MBA is best for make better career. Best Of LucK ! If my answer is best for u go to my account ,then u click follow Nishant B

Yes, you can do but you wiil have to start fresh, compete with the freshers, pass the required PET exam and then take admission in an engineering college.