Coupling efficiency = NA2 such that if you have an initial power output P0 you get

P=P0*NA2

in certain power amplifiers(cls A,cls C etc.) the output sometimes not directly taken. rather it's coupled with transformer and then transferred power is applied to the load..this is transformer coupling.....

there are two main reasons to do so

1. in order to increase the efficiency.(exmpl: efficiency of class A power amplifier increase by almost 25%)

2.in order to get smooth i.e; distortion less output..

by Jishnu Mukherjee

(Kolkata,India)

input force x input distance > output force x output distance -Novanet

Output force

Efficiency = Output/Input.