Peak Versus RMS Voltage

Looking back at the bottom of page 154, why is the voltage 9 instead of 6 The answer is related to the fact that the maximum part of the sine wave in the wall 

It turns out that to determine the effective value of a sine wave, you have to do the following. First divide up the top half of the ac into very small slices (the increments of calculus), and then square each one of these short-term voltages. The next step is to figure out the average value (the mean ) of these squared slices. Then take the square root of this mean. This is called the root mean square voltage, or RMS. It is not the same as the simple average, and also it does not work for odd shapes such as sawtooth waves. 

Another way to get full wave rectification is shown in Fig. 14.7. It does not require a center tapped transformer, but it does use two more diodes. It gives a higher output voltage, because the negative output wire does not have to come from a center tap. (The output is 12 times 1.414, or 17 volts.) 

What comes out of the bottom of the coil is now positive, so it goes through diode D, further charging the positive side of the capacitor. The inductor and capacitor together make up a good low pass, LC filter (see index), so the output current is relatively free of ripples. 

The circuit of Fig. 14.7 (and the ones of Figs. 14.8 and 14.9) could be assembled by the experimenter as an optional exercise, but this would require sharing extra components with another experimenter or another laboratory group. 

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