The Attempt at a Solution
The force between the plates is given by (1/2)QE ,where Q is the charge on the plates and E is the electric field between the plates .
Now Q = CV and E = V/d , where C is the capacitance , V is the potential difference and d is the plate separation . So , force can be written as F = (1/2)(CV)(V/d) .When dielectric is inserted C changes to "kC" .V doesn't change as the plates are connected to battery .
So , force F increases by a factor "k'" to become kF on insertion of the dielectric while plates are connected to battery .
Is my work correct ?