On 29/12/16 09:12, Francisco Olarte wrote:
On Wed, Dec 28, 2016 at 5:53 PM, Jan de Visser <jan@xxxxxxxxxxxxx> wrote:
.....but the term "impedance mismatch"
is at least 25 year old;
Much older, I was told it in class at least 32 years ago.
as far as I know it was coined
_Borrowed_ from electrical engineering / communication techs.
It is used to highlight how signals 'bounce' at the points of a
transmision path where impedances do not match. It extrapolates the
fact that if you have a battery with an internal resistance R the way
to extract the maximum energy on a load is for it to match the
impedance, be R too. Higher load impedance and the fraction of energy
in the load goes up, the total down. Lower load impedance and the
fraction in the load goes down, the total up. In either case absolute
power in the load goes down. Match the impedance and the energy in the
load is the maximum ( and equal to the internal loss in the battery ).
[...]
From my distant memory of studying AC stuff at University many moons ago...
You want the two impedances to be complex conjugates of each other (this
means the MAGNITUDES will be equal) - which means the phase change
should be equal & opposite, and the resistance to match.
Cheers,
Gavin
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