Circuite electrice cu bifurcatii

Analogie electricitate – curgerea fluidelor

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Una dintre cele mai simple modalități de a înțelege conceptele de baza ale electricității este de a apela la o analogie cu modul de curgere al fluidelor, pe care îl înțelegem intuitiv din experiența proprie. Astfel, să ne închipuim apa curgând printr-un mecanism de țevi, de diverse diametre.

Să ne închipuim că avem pompe care împing apa prin țevi, pompe cu puteri diverse. Acum, dacă în loc de apa ne închipuim un flux de electroni, în loc de țevi, fire conductoare și  în loc de pompe surse de tensiune (baterii sau alimentatoare), obținem o analogie care funcționează aproape perfect pentru a înțelege teoria electricității.

Astfel, la un moment dat printr-o anumita țeavă trece o anumita cantitate de apa. La fel, printr-un fir, la un moment dat trece o anumita cantitate de curent. Cât de mult curent trece printr-un fir la un moment dat este un element caracterizat de intensitatea curentului electric, măsurată în Amperi.

Dacă ne închipuim un circuit format din mai multe țevi mufate între ele sub forma unui circuit închis, este clar că prin fiecare țeavă circulă exact aceeași cantitate de apa la un moment dat (apa pleacă din pompa, trece prin fiecare țeavă, și  apoi se întoarce înapoi în pompă, exact câtă apa pleacă, exact atâta se întoarce). Exact în același mod, intensitatea curentului electric este aceeași în oricare punct al unui circuit electric simplu (fără bifurcații). Altfel spus, prin oricare punct al unui circuit fără bifurcații trece aceeași cantitate de curent.

Mai departe, dacă ne gândim că țevile au diametre diferite, dar prin ele circula aceeași cantitate de apă, atunci presiunea apei este diferită în fiecare țeavă, în funcție de diametrul acesteia. Echivalentul presiunii apei din țevi, în cazul curentului electric, este potențialul electric (sau tensiunea) și  se măsoară în Volți.

Dacă ai udat vreodată cu furtunul în gradină, atunci știi ca pentru a creste presiunea apei, tot ce ai de făcut este să strângi furtunul (sa-i micșorezi diametrul). Diametrul țevii (practic, rezistenta pe care o opune țeava trecerii apei) este echivalentul în cazul circuitelor electrice cu rezistenta elementului electric, și  se măsoară în Ohm.

Exista elemente electrice speciale, care se cheamă rezistoare și  care sunt folosite tocmai pentru rezistenta cu care se opun trecerii curentului electric. Dacă ne gândim că în cazul furtunului cu apa, cu cât diametrul furtunului este mai mic (deci rezistenta opusă apei este mai mare) cu atât presiunea apei este mai mare, atunci putem scrie : intensitatea = tensiunea / rezistenta

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Analogie electricitate – curgerea fluidelor

  • Una dintre cele mai simple modalitati de a intelege teoria electricitatii este de a apela la o analogie cu modul de curgere al fluidelor, pe care il intelegem intuitiv din experienta proprie. Astfel, sa ne inchipuim apa curgand printr-un mecanism de tevi, de diverse diametre. Sa ne inchipuim ca avem pompe care imping apa prin tevi, pompe cu puteri diverse. Acum, daca in loc de apa ne inchipuim un flux de electroni, in loc de tevi, fire conductoare si in loc de pompe surse de tensiune (baterii sau alimentatoare), obtinem o analogie care functioneaza aproape perfect pentru a intelege teoria electricitatii. Astfel, la un moment dat printr-o anumita teava trece o anumita cantitate de apa. La fel, printr-un fir, la un moment dat trece o anumita cantitate de curent. Cat de mult curent trece printr-un fir la un moment data este un element caracterizat de intensitatea curentului electric, masurata in Amperi. Daca ne inchipuim un circuit format din mai multe tevi mufate intre ele sub forma unui circuit inchis, este clar ca prin fiecare teava circula exact aceeasi cantitate de apa la un moment dat (apa pleaca din pompa, trece prin fiecare teava, si apoi se intoarce inapoi in pompa, exact cata apa pleaca, exact atata se intoarce). Exact in acelasi mod, intensitatea curentului electric este aceeasi in oricare punct al unui circuit electric simplu (fara bifurcatii). Altfel spus, prin oricare punct al unui circuit fara bifurcatii trece aceeasi cantitate de curent. Mai departe, daca ne gandim ca tevile au diametre diferite, dar prin ele circula aceeasi cantitate de apa, atunci presiunea apei este diferita in fiecare teava, in functie de diametrul acesteia. Echivalentul presiunii apei din tevi, in cazul curentului electric, este potentialul electric (sau tensiunea) si se masoara in Volti. Daca ai udat vreodata cu furtunul in gradina, atunci stii ca pentru a creste presiunea apei, tot ce ai de facut este sa strangi furtunul (sa-i micsorezi diametrul). Diametrul tevii (practic, rezistenta pe care o opune teava trecerii apei) este echivalentul in cazul circuitelor electrice cu rezistenta elementului electric, si se masoara in Ohm. Exista elemente electrice speciale, care se cheama rezistoare si care sunt folosite tocmai pentru rezistenta cu care se opun trecerii curentului electric. Daca ne gandim ca in cazul furtunului cu apa, cu cat diametrul furtunului este mai mic (deci rezistenta opusa apei este mai mare) cu atat presiunea apei este mai mare, atunci putem scrie : intensitatea = tensiunea / rezistenta  

    Citește și :

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