21) A three phase halfwave rectifier has an AC input of 415 V 50 Hz. The ripple frequency of DC output in pulses/sec is

22) A 3-phase full wave rectifier has an AC input of 415 V, 50 Hz. The ripple frequency of D.C. output in pulses per second is

23) You have to measure the ripple voltage of a DC power supply to confirm with that of the manufacturer's specification. What is the instrument you need for this measurement ?

24) Which type of filter can be used together with a full wave rectifier only ?

25) What is the current flowing through each diode in a full wave rectifier ?