Science

Yes in some institutes and No in some institutes, it's possible to study M.Sc. In Physics after B.Tech in Mechanical Engineering. But only few colleges are giving chance for B.Tech students like Delhi University. Do some research about colleges giving this chance and join accordingly.
You would only be accepted to a few institutions if you wanted to pursue an MSc in physics. Traditional universities will not even accept you for a master's degree in physics. Furthermore, btech mechanical engineering is solely based on basic classical mechanics or lower level classical mechanics, the majority of which is newtonian mechanics.
BSc physics is focused on quantum mechanics, and almost all areas of study in BSc physics use quantum mechanics like there isn't any newtonian mechanics in the universe, so whatever they would be thinking in India about degree equivalence, a BSc physics is way higher than a btech mechanical engineering in terms of theoretical knowledge and depth of physics and mathematics, in fact, a BSc physics is way higher than btech, So, if you get into one of those select few universities, you'll have to work extremely hard or you'll end up in hell. Also, if you want to study physics overseas, a btech is ineligible for an MSc or MS in physics. Only those with a BSc/BS in physics are eligible. As a result, you won't be able to pursue an MSc in another country because their qualifying standards only allow for BSc/BS physics.

You can do Masters in psychology being a B.Tech CSE graduate. It's quite easier to switch now to Masters psychology. Get ready to do hardwork since you are not a psychology background student. Few colleges won't allow non psychology background students, check before and join accordingly!
Without a bachelor's degree in psychology, you can pursue an MA or MSc in psychology. The eligibility requirements will differ from one university to the other. Many leading colleges provide an MA in Psychology to graduates with a 50 percent graduation rate. So, if you have a B.Tech with a grade point average of greater than 50%, you can apply.
Some colleges grant admission to courses based on their degree grades, while others grant admission based on their entrance exam rank. In addition to the written test, some universities will conduct an oral examination. Almost all major institutions offer this subject, which you may research on the university's website.

There are various choices in Science stream. First select MPC or BiPC. If you want to go for medicine related jobs take BiPC. If you want to go for engineering side take MPC.
Choosing a job path is one of the most life-changing decisions a person can make. It determines their career and personal paths in the future and serves as a stepping stone to the millions of aspirations they have cherished. Science students have a plethora of career opportunities.
The study of the three branches of science, physics, chemistry, and biology, creates a whole new universe of possibilities, spanning from space exploration to the study of sand and soil.
The days are gone where it is considered that science students can only work as doctor or engineer.
Career options :
Artificial intelligence
Machine learning
Data science
Business analytics
Blockchain developer
Software designing
Spacetech
Geology
Forensic pathologist
Technical writer
Astrophysicist