1soin/ECA/UD4/Teoria: Inpedantzia
Sarrera
Ohmen legea: hiru elementu
Material eroaleak, ez eroaleak eta isolatzaileak:
25ºtan materialek erresistentzia ezberdin eguten dute (ohmino/metrotan), adibidez, zilarra: 1,59*10^-8, kobrea: 1,71*10^-8, urrea: 2,35*10^-8.
Tenmperatura igo ahala, erresistentzia gehiago.
[math]\displaystyle{ R= \frac {P\cdot l}{S} }[/math], non P= material bakoitzaren erresistentzia, l=luzera eta s=sekzioa.
Definizioa
Elementu bereziekin, erresistentzia mota bereziak sortzen dituzte: induktoeak - induktantzia; kondentsadoreak (capacitors) - kapazitantzia. Bien batuketa erreaktantzia deitzen zaio. Erreaktantzia + erresistentzia = inpedantzia.
Frekuentziarekiko balio ezberdina dauka erreaktantzia, berez, inpedantzia baita.
Inpedantziaren ikura Z da, Z_load sarrerakoa bada eta Z_source irteerakoa.
Beste era batean definititua, inpedantzia korronte alternoak sortzen duen erresistentzia da.
Historia
For audio circuits, is it important to match impedance?
Not any more. In the early part of the 20th century, it was important to match impedance. Bell Laboratories found that to achieve maximum power transfer in long distance telephone circuits, the impedances of different devices should be matched. Impedance matching reduced the number of vacuum tube amplifiers needed, which were expensive, bulky, and heat producing.
In 1948, Bell Laboratories invented the transistor — a cheap, small, efficient amplifier. The transistor utilizes maximum voltage transfer more efficiently than maximum power transfer.
Matching inpedance
For maximum voltage transfer, the destination device (called the "load") should have an impedance of at least ten times that of the sending device (called the "source"). This is known as BRIDGING. Bridging is the most common circuit configuration when connecting audio devices. With modern audio circuits, matching impedances can actually degrade audio performance.
http://shure.custhelp.com/app/answers/detail/a_id/224
Inpedantzia eta voltaje
http://unicrom.com/valor-rms-promedio-pico/
0,707= 1/√2.
