the action and reaction do not lead equilibrium if action and reaction force react on different objects
The voltage<span> difference between the two plates can be expressed in terms of the </span>work<span> done on a positive test charge q when it moves from the positive to the negative plate.</span><span>
E=V/d
where V is the voltage and d is the distance between the plates.
So,
E=6.0V/1mm= 6000 V/m. The electric field between the plates is 6000 V/m.</span>