I am not sure about the geometry of the problem. However, coplanar waveguide - coplanar transmission lines are quite common in microwave technique. Such lines are quite well known (I mean there is analytic formulation for field strength).  Try Transmission line design handbook by Brian C. Wadell. 

I am afraid that you can not simply divide the voltage drop by the gap width. The field is not homogeneous (provided I understand well the geometry).

If I understand you correctly there is an electrical field strenght of 5 MV/m between the electrodes. As an electrical breakdown under atmospheric conditions will  occur at 3 MV/m  already a plasma is prevailing between the electrodes, thus no field lines are at hand.

Dear Gunter Sir,

I am trying to actuate and move the drop at this high electric field. And I am having drop movement in the order of mm/s. So this indicate that field exists. Papers have been reported also for drop movement and rivulet formation even at 7MV/m. 

Could you please comment on this.

http://scitation.aip.org/content/aip/journal/jap/89/2/10.1063/1.1332799

Link to the above commented paper

Dear Krishnadas,

Sorry to say that I have no other idea for your problem

Günter

Most of the field will concentrate in the gap while some inhomogeneous stray field will form 'arc-like' field lines off the plane (underneath and above). According to your 'scitation', one would expect the drop to move to the middle of the gap . . . and stay there. No more moves once it has reached the point of maximum field strength - no matter what voltage is applied. Until some plasma discharge happens - most likely vaporizing the drop.