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.
If the average of the full cycle was taken it would of course be zero, as in a sine wave symmetrical about zero, there are equal excursions above and below the zero line. Using only half a cycle, as illustrated in fig 1.2.3 the average value (voltage or current) is always 0.637 of the peak value of the wave.