Impedance matching
= Impedance matching
{wiki}
For a source with internal <electrical impedance> $Z_s$, conjugate matching $Z_L=Z_s^*$ maximizes delivered mean <power> when the source is fixed. For a purely resistive source and equal load <electrical resistance> $R$, the load sees half the open-circuit <voltage>. A <Johnson-Nyquist noise> source with open-circuit mean-square voltage $4k_BTR\,d\nu$ therefore delivers $k_BT\,d\nu$ to the matched load, rather than $4k_BT\,d\nu$.