Simple explanation of ac to dc. The ac at input changes its polarity 50 times a second (60 in the USA). The above image is deliberately made slow at the rate of 1 per second to understand the same. Watch the output DC in red that remains always +ve. and black -ve. This dc, however, is not pure DC it is called pulsating DC though it can be used for some applications. To get pure DC a lot of filtering is needed.
The Smoothing Capacitor
We know that the single stage half-wave rectifier creates a yield wave each half cycle and that it was not viable to utilize this sort of circuit to deliver a relentless DC supply. The full-wave span rectifier, on the other hand, gives us a more prominent mean DC esteem (0.637 Vmax) with less superimposed pulsating while the yield waveform is twice that of the recurrence of the information supply recurrence. We can in this way expand its normal DC yield level considerably higher by uniting a suitable smoothing capacitor over the yield of the extension circuit as demonstrated as follows.