According to https://www.caluniv.ac.in/admission/mtech_2016-17/APL_PHY.pdf , to be eligible to study M.Tech in Applied Physics, Candidates should have secured a minimum aggregate of 60% or equivalent in BE/B.Tech and also have a valid GATE score. So it is mandatory for you to appear for GATE and have a valid score if you want to pursue M.Tech in Applied Physics from Calcutta University.