The efficiency of a full wave rectifier (81.2%) is too double of a half wave rectifier(40.6%) because the r.m.s. value in case of a full wave rectifier is Maximum current divided by 1.41 (under root of 2) whereas in case of a half wave rectifier the r.m.s current is half of maximum current during the wave cycle.
Half wave rectifier
These type of rectifier converts only one half of AC into DC signal, either positive or negative cycle. As it rectifies AC partially its efficiency is also less. Maximum efficiency is 40.6%. Half wave rectifier needs only single diode for rectification.
Full wave rectifier
It converts entire AC into fluctuating DC that is it covert both half cycle to DC. Therefore its efficiency is almost double of half wave rectifier. Efficiency is 81.2 %. It consist of more than one diode. Here positive half cycle is converted by one diode and negative half cycle is converted by other diode. Commonly used full wave rectifier are
Centre tapped full wave rectifier and bridge rectifier.
first you have to know that What is Rectifier ?
Rectifier is device which coverts an alternating voltage or current (ac) into a unidirectional voltage or current (dc).
Half Wave Rectifier
In this rectifier only one diode and step down transformer are use.
In half wave rectifier, it is work only during one half cycle of the ac supply.
maximum rectification efficiency is 40% i.e. is very poor.
Full Wave Rectifier
In this rectifier two diodes and center tapped transformer are use.
In full wave rectifier, it is work in both the half cycles of ac supply.
maximum rectification efficiency is 82%