In a full wave rectifier (consisting of 2 diodes), ac is converted into DC. Confusing part is I know how the rectification is done, but still how the input ac current (consisting of both negative and positive currents) is converted into positive DC current????? 
How this negative current is converted into positive DC current?
Best Answer
That schematic is confusing as it appears that everything is happening simultaneously. Let's look at each half-cycle of the AC supply.
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) A centre-tapped full-wave rectifier. (b) Effective circuit when dot-end is positive. (c) Effective circuit when dot-end is negative.
The end result is that a pulse of current is alternately given by the upper and lower diode on each half-cycle of the AC supply voltage.
simulate this circuit
Figure 2. Schematic redrawn in same format as that in the question.