Measuring cup, graduated cylinder, anything that has volumetric markings to tell you how much liquid you have. Or if the liquid has a known density, you can weigh it and determine its volume from mass/density. (You just have to make sure your units are all the same scale--if you weigh in lbs. and have density in grams/cubic centimeters, you have to convert lbs. to grams before using the density equation.
I know the basics of how to find these values from a graph, but not sure how to prove that average voltage of half-wave rectifier is peak/pi and rms is peak/2. Same for full-wave rectifier where average is 2peak/pi.
Full-wave (full bridge) rectifiers construct a bridge of diodes to convert the whole of the input voltage to one of constant polarity. This is more efficient than the half wave rectifier as it allows both the positive and negative components of the input voltage to be utilised in building the DC voltage.