49. The capacitance of a parallel plate capacitor with air as medium is 6μF. With the introduction of a dielectric medium, the capacitance becomes 30μF. The permittivity ?

44. A parallel plate air capacitor of capacitance C is connected to a cell of emf V and then disconnected from it. A dielectric slab of dielectric constant K, which can just fill the air gap of the capacitor, is now inserted in it. Which of the following is incorrect ?

42. Two thin dielectric slabs of dielectric constants K1 and K2 ( K1 < K2) are inserted between plates of a parallel plate capacitor, as shown in the figure. The variation of electric field ’E’ between the plates with distance ’d’ as measured from plate P is correctly shown by ?

39. Two parallel metal plates having charges +Q and −Q face each other at a certain distance between them. If the plates are now dipped in kerosene oil tank, the electric field between the plates will ?

28. A parallel plate condenser with oil between the plates (dielectric constant of oil K = 2 ) has a capacitance C. If the oil is removed, then capacitance of the capacitor becomes ?