SAVA+SEBASTIAN

Efectul Magnetic

**Curentul electric **poate devia un ac magnetic. Acest lucru a fost demonstrat de un fizician danez, Cristian Oersted (1777-1851), in 1820. El a fost primul care a stabilit legatura care exista intre electricitate si magnetism. In 1831, fizicianul englez Michael Faraday (1791- 1887) a facut experienta inversa: el a demonstrat ca miscarea unui magnet poate produce un curent electric. Inventator si pasionat al experimentelor, el a pus bazele unei noi stiinte, electromagnetismul, care studiaza actiunile reciproce ale electricitatii si magnetismului.  **Magnetismul natural ** Un magnet atrage pilitura de fier, de nichel si de cobalt sau a altor substante care au in componenta aceste metale. Aceste trei metale, numite si “feromagnetice”, sunt singurele care au aceasta proprietate. Mai mult, daca punem o bucata de metal feromagnetic in contact cu un magnet, ea va capata proprietati feromagnetice.Magnetizarea se transmite, deci, la distanta si prin contact direct. Zona care inconjoara un magnet si in care se manifesta fortele magnetice se numeste “camp magnetic”.   **<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 19px; text-decoration: none; vertical-align: auto;">Campul magnetic produs de un curent electric ** <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Un fir conductor drept, strabatut de un curent electric, creeaza in jurul lui un camp magnetic. Daca firul formeaza o bucla, campul magnetic o va strabate. Este ceea ce se intampla cu campul magnetic al unei bare magnetizate, o tija de fier, de exemplu. Pentru a crea un camp magnetic mai intens, putem infasura un fir conductor pe un cilindru. Acest camp poate fi intensificat daca introducem o bara magnetica de-a lungul axei acestui cilindru: acesta constituie principiul de functionare a unei bobine magnetice, sau solenoid, numita si “electromagnet”. <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Un electromagnet este un obiect simplu si foarte util, caci permite crearea unui camp electromagnetic oriunde este plasat. El constituie elementul de baza in orice aparat electromagnetic. La o sonerie electrica, de pilda, un electromagnet actioneaza un ciocan care loveste un clopotel. <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;"> <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;">**<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Curentul electric produs de un magnet ** <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Daca curentul electric creeaza un camp magnetic, la randul lui, campul magnetic poate produce un curent electric, numit “curent indus”. Acesta constituie principiul inductiei electromagnetice. Anumite **<span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-align: left; text-decoration: none; vertical-align: auto;">generatoare ** de curent functioneaza pe acest principiu. Ele sunt alcatuite dintr-un magnet care are o miscare oscilatorie in raport cu o bobina: astfel se produce un curent care-si schimba sensul. Aceste generatoare de curent alternativ se numesc **<span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-align: left; text-decoration: none; vertical-align: auto;">alternatoare. ** <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"> <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;">//<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;">__<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: underline; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: underline; vertical-align: auto;">Magnetism si electromagnetism __ // <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Exista alternatoare de toate marimile, de la cele mici (dinam), folosite la alimentarea farurilor unei biciclete, si pana la uriasele grupuri turbo-alternatoare folosite in centralele electrice. <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;">**<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Principiul inductiei electromagnetice ** <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">O mica bobina conductoare este conectata la un aparat de masura fara sa fie strabatuta de nici un curent electric. Acul aparatului nu se misca. Atunci cand introducem o bara magnetica in bobina, acul aparatului inregistreaza o miscare intr-o anumita directie. Miscarea magnetului creeaza un curent electric in bobina. Atunci cand indepartam bara magnetica, acul aparatului se misca in celalalt sens. Astfel se demonstreaza producerea unui curent care circula in sens opus. Acest curent, care isi schimba sensul, este un curent alternativ. Spunem, de asemenea, ca miscarea barei magnetice induce un curent alternativ. Aceasta experienta a fost realizata de fizicianul englez Michael Faraday, in 1831. El a demonstrat astfel existenta inductiei electromagnetice. <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"> <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;">**<span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Alternatorul ** <span style="background-color: transparent; color: #000000; font-family: Times New Roman; font-size: 16px; text-align: left; text-decoration: none; vertical-align: auto;"><span style="background-color: transparent; color: #545353; font-family: Tahoma; font-size: 11px; text-decoration: none; vertical-align: auto;">Un alternator, sau generator de curent alternativ, este un sistem ingenios de producere a energiei electrice cu ajutorul unui magnet. El este alcatuit dintr-o bobina conductoare, patrata, care se roteste in campul magnetic al unui magnet fix. Aceasta miscare induce (sau produce) in bobina un curent care isi schimba sensul (altfel spus un curent alternativ). Acest curent trece prin inelele colectoare care se rotesc impreuna cu bobina. Niste perii fixe, care sunt in contact cu aceste inele, aduna curentul si il canalizeaza pentru a putea fi utilizat.