Question

why is the force on the -ve charge is opposite to field on it (i ask about the physical meaning not the mathematical)

Answer 1

We take attractive force as negative and repulsive force as positive

Answer 2

The direction of an electric field is defined to be the direction a positive charge would move if it experienced the field. Necessarily, a negative charge has to move in the opposite direction. We could have defined it the other way around, of course.

Answer 3

cos field is due to 2 opp plates...and -ve charge wants too get 2wards +plate which is opp to the field...