What is a rectifier? Explain the working of half wave and full wave rectifiers with diagrams

Rectifier:The device used to convert alternating voltage or current into direct voltage or current is called a rectifier. The process of doing this is called rectification.
Working of half wave rectifier :
i) Half wave rectifier converts only one half cycle of A.C signal into D.C signal.
ii) Half wave rectifier can be constructed with a single p-n junction diode as shown in the diagram

iii) The input a.c signal to be rectified is applied across the primary of the transformer and output D.C signal is taken across the load resistance (R_L) connected across secondary.
iv) For all the positive half cycles of input A.C signal diode is in forward bias and hence conducts current so current passes through load resistance (R_L)
v) For all the negative half cycles of input A.C signal the diode D is in reverse bias and hence does not conduct current. So no current passes through load resistance (R_L)
vi) In this way only positive half cycle of input AC signal is converted into rectified D.C signal.
$\mathrm{\eta }=\frac{\text{ out put D.C power }}{\text{ input A.C power }}=\frac{0.406{\mathrm{R}}_{\mathrm{L}}}{{\mathrm{r}}_{\mathrm{f}}+{\mathrm{R}}_{\mathrm{L}}}$
R_L- load resistance, r_f- forward resistance of diode maximum efficiency is 40.6%
Working of full wave rectifier :
i) Full wave rectifier converts both the half cycles of A.C signal into D.C signal
ii) It can be constructed with two p-n junction diodes as shown below

iii) The input A.C signal to be rectified is applied across primary of transformer and rectified output D.C signal is taken across load resistance connected across the secondary of transformer.
iv) The secondary of transformer is centre tapped and with respect to centretap 'c' the inputs of the diodes A and B are out of phase.
v) For all the positve half cycles of input A.C signal the diode D₁ is in forward bias and hence it conducts current .The diode D₂ is in reverse bias and hence it does not conduct current.
vi) For all the negative half cycles of input A.C signal the diode D₂ is in forward bias and hence it conducts current .The diode D₁ is in reverse bias and does not conducts current.
vii)In this way both positive and negative half cycles of input A.C signal are converted into rectified D.C output
viii)Efficiency of full wave rectifier is 
$\mathrm{\eta }=\frac{\text{ out put D.C power }}{\text{ input A.C power }}=\frac{0.812{\mathrm{R}}_{\mathrm{L}}}{{\mathrm{r}}_{\mathrm{f}}+{\mathrm{R}}_{\mathrm{L}}}$
maximum efficiency is 81.2%