Between the plates of a parallel plate capacitora dielectric plate is introduced just to fill the space between the plates. The capacitor is charged and later disconnected from the battery. The dielectric plate is slowly drawn out of the capacitor parallel to the plates. The plot of the potential difference across the plates and the length of the dielectric plate drawn out is [MP PET 1997]

While drawing the dielectric plate outside, the capacitance decreases till the 

entire plate comes out and then becomes constant. So, V increases and 

then becomes constant.