17) The capacity of a parallel plate air capacitor is 5 micro F. If the air is replaced by glass, the capacity gets increased to 40 micro F. Hence the permittivity of the glass is :

18) The total capacity of two capacitors of 2 micro F each connected in series will be equal to :

19) The static electrical energy stored in a capacitor of 1.2 micro F at 3000 volts P.D. will be equal to :

20) The unit of capacitance is

21) If two capacitors of 2 micro F and 3 micro F are connected in series and then this group is connected across a capacitor of 4 micro F, the total capacity will be :