The difference between peak positive and peak negative values of an A.C. voltage is called :

9) The r.m.s value of A.C. is equal to :

10) The value of form factor for a pure sine-wave is :

11) If the voltage and current have a phase difference of 90 degree in an A.C. circuit, the power will be :

12) Which one of the following frequencies has the longest time period ?