SOLUTION TO Q.67

see to solve this question u must know the expression for force experienced by a dielectric slab kept inside a capacitor. Suppose a capacitor with length and width of the plated l and b respectively. the seperation between the plated is d. now a dielectric slab of dielectric constant K is kept between the plated of the capacitor such tht x length is inside the capacitor and the width of the dielectric is also d. then the dielectric is pulled inside the capacitor with a force given by

now let the length of the dielectric be 2x so tht x length remains inside each capacitor. now for the slab to be in equilibrium the forces exerted by both the capacitors must be equal in magnitude. applying the above formula

solving this u will get

i will soon post solution to q.68 coz. its very tedious to type the complete solution here.

PLZ... RATE ME IF U UNDERSTOOD THE SOLUTION CLEARLY OR IF IN DOUBT U CAN ASK FURTHER.