Since the potential difference between the plate is the integral
of the field vector against the distance, E has to be the same in both
capacitors. The free charge "stored" on the plates will be six times
higher for the one with dielectric, but the adjacent layer of bound charge
will ensure that the net electric field is the same as for the capacitor
with no dielectric.
Mark
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
P.O. Box 6866
Fullerton, California 92834-6866