Question

When a dielectric is inserted between the plates of a charged parallel plate capacitor, fully occupying the intervening region, how does the polarization of the dielectric medium affect the net electric field ?

Answer 1

The electric field between the capacitor plates is reduced by the presence of the dielectric because the induced surface charges on the dielectric cause an electric field in the opposite direction of the original field in the charged capacitor. These fields tend to cancel each other resulting in a reduction of the original field.