{"id":26013,"date":"2011-03-30T13:44:00","date_gmt":"2011-03-30T13:44:00","guid":{"rendered":""},"modified":"2020-09-25T09:39:47","modified_gmt":"2020-09-25T09:39:47","slug":"electrostatica-fenomene-fundamentale-2","status":"publish","type":"post","link":"https:\/\/rubyskynews.com\/index.php\/2011\/03\/30\/electrostatica-fenomene-fundamentale-2\/","title":{"rendered":"ELECTROSTATICA FENOMENE FUNDAMENTALE"},"content":{"rendered":"
<\/div>
OBIECTUL ELECTROSTATICII .Putem constata experimental ca unele corpuri, de pilda rasina, ebonita, ceara rosie sau sticla capata insusirea sa atraga obiecte usoare : fulgi de pasare, fire de bumbac sau bucatele de hartie, dupa ce le frecam cu o stofa de lana, cu o blana sau cu o bucata de matase. <\/span>Aceasta insusire dispare destul de repede, dar poate sa reapara dupa o noua frecare.<\/span> <\/span>Fenomenul o fost observat mai intai la chihlimbar. Filozoful grec <\/span>Thales din Milet<\/span><\/i>, care trait acum 2500 de ani, este primul care-l aminteste, doar ca o simpla curiozitate si spune ca l-a aflat de la o tesatoare. Apoi a cazut in uitare.<\/span> <\/span>Abia pe la 1600 medicul englez Gilbert, reluan cercetarile, constata ca mai sunt si alte corpuri, cu aceeasi propietate si, dupa numele grecesc al chihlimbarului( elektron), numeste <\/span>electrizare<\/span><\/u><\/i> fenomenul care le aduce in aceasta situatie.<\/span> Vom spune deci ca acele corpuri se electrizeaza prin frecare, sau ca se incarca cu electricitate. Timp de aproape 200 de ani, studiul electricitatii s-a limitat apoi la o acumulare treptata de observatii calitative.<\/span><\/div>\n
            Legatura cantitativa s-a putut stabili numai dupa ce incercarile lui <\/span>Cavendish, Priestley<\/span><\/i> sau <\/span>Daniell Bernoulli<\/span><\/i>, urmate de cercetarile sistematice ale lui Charles Auguste de Coulomb au dus la formularea matematica a legii de interactiune, din care putem calcula fortele dezvoltate si stabili unitatile de masura pentru ceea ce numim <\/span>cantitate de electricitate <\/span><\/i>ori <\/span>sarcina electrica<\/span><\/i>.<\/span><\/div>\n
            De aici inainte intrm pe teritoriul adevaratei cercetari stiintifice, prin care determinarile din laborator, unite cu calculul matematic, au dus, in cateva decenii, la inchegarea electrostaticii.<\/span><\/div>\n
                        <\/b><\/span>Electrostatica este studiul electricitatii in echilibru.<\/span><\/b><\/div>\n
            <\/span>Pentru observarea calitativa a interactiunilor electrice, putem folosi un dispozitiv simplu si usor de realiza : pendulul electric.<\/span><\/div>\n
            El consta intr-o bobita usoara, din pluta sau de maduva de soc, atarnata cu un fir subtire de matase, pe un suport convenabil.<\/span><\/div>\n
            Aceasta bobita poate fi, eventual inlocuita prin cilindrul de hartie al unei tigari, golita de tutun.<\/span><\/div>\n
\n<\/div>\n
LEGEA LUI COULOMB<\/span><\/div>\n
            In 1785, Coulomb a gasit experimental relatia cantitativa care exprima forta de interactiune, in functie de sarcinile electrice in przenta si de distanta respectiva.El s-a servit de o balanta de torsiune.<\/span><\/div>\n
            O bara izolanta, cat mai usoara, este suspendata cu ujn fir subtire. Ea poarta, la un capat, o mica sfera conductoare, iar la capatul opus e lipita o aripioara de hartie, care amortizeaza oscilatiile si, totodata echilibreaza greutatea sferei.<\/span><\/div>\n
O a doua sfera, egala in diametru, este fixata rigid, pe un suport izolant, la nivelul primei si la aceeasi distanta, fata de firul de suspensie al barei.<\/span><\/div>\n
Tot sistemul este introdus intr-un cilindru protector, de sticla, unde o substanta higroscopica absoarbe vaporii de apa, ca sa asigure o cat mai buna izolare. <\/span><\/div>\n
\n<\/div>\n
1.In prima seriie de  ercetari, se incarca ambele sfere cu cate o sarcina electrica oarecare. Ele se atrag sau se resping si, cu ajutorul unghiului de torsiune al firului, putem determina forta de interactiune.<\/span><\/div>\n
Rezultatul experientelor ne duce la concluzia ca aceasta forta este invers proportionala cu patratul distantei dintre centrele sferelor.<\/span><\/div>\n
\n<\/div>\n
2.In a doua srie de cercetari, cele doua sfere, prealabil electrizate, sunt descarcate treptat, prin atingere cu o a treia sfera izolata, de aceeasi marime, dar neelectrizata.<\/span><\/div>\n
Prin atingeri succesive, se poate reduce sarcina oricareia din sfere, intai la jumatate din valoarea initiala, apoi la un sfert si asa mai departe.<\/span><\/div>\n
\n<\/div>\n
Rasucind capatul de sus al firului de suspensie, asa ca sa reducem, de fiecare data, sferele la distanta la care se gaseau inainte de electrizare, unghiul de torsiune respectiv ne permite iarasi sa calculam forta de interactiune, pentru diferitele valori ale sarcinilor.<\/span><\/div>\n
Iar daca notam cu <\/span>Q<\/span><\/i> si <\/span>Q\u2019 <\/span><\/i> sarcinile initiale, constatam experimental ca, dupa diferitele descarcari succesive,<\/span><\/div>\n
pentru sarcinile <\/span> Q<\/span><\/i> si <\/span>Q\u2019<\/span><\/i>     forta masurata este <\/span>F<\/span><\/i><\/span><\/div>\n
pentru sarcinile  <\/span>Q\/2<\/span><\/i> si <\/span> Q\u2019<\/span><\/i>  forta masurata este <\/span>F\/2<\/span><\/i><\/span><\/div>\n
pentru sarcinile  <\/span>Q\/2<\/span><\/i> si <\/span>Q\u2019\/2<\/span><\/i> forta masurata este <\/span>F\/4<\/span><\/i><\/span><\/div>\n
si asa mai departe.<\/span><\/div>\n
            De aici se vede ca, indiferent de unitatile in care am exprima sarcinile electrice, <\/span>forta de interactiune, la o distanta data, este proportionala cu produsul lor.<\/span><\/i><\/span><\/div>\n
\n<\/div>\n
            Aceste doua serii de cercetari ne duc impreuna la concluzia ca forta de interactiune F, intre doua corpuri, incarcate ce sarcinile Q1<\/sub> si Q2<\/sub> si situate la distanta  r , se poate exprima prin relatia :<\/span><\/div>\n
                                                     <\/span><\/span><\/span><\/b><\/div>\n
in care constanta de propartionalitate \u03b5 caracterizeaza mediul separator, din punct de vedere electric si se numeste <\/span>constanta dielectrica <\/span><\/i>sau <\/span>permitivitate.<\/span><\/i><\/span><\/div>\n
            Valoarea ei numerica si dimensiunile fizice depind de sistemul unitatilor folosite.<\/span><\/div>\n
\n<\/div>\n
                        Aceasta relatie, fundamentala in electrostatica, exprima <\/span>legea lui Coulomb.<\/span><\/i><\/b><\/span><\/div>\n
\n<\/div>\n
            Cantitatile de electricitate Q, pe care le-am  numit <\/span> sarcini elecrice<\/span><\/i> vor fi considerate ca punctiforme, adica raspandite pe corpuri cu dimensiuni geometrice practic neglijabile, in comparatie cu distanta care le separa.<\/span><\/div>\n
            <\/span><\/div>\n
            <\/span>Formula lui Coulomb este analoga cu formula lui Newton, prin care am exprimat fortele de interactiune ale maselor gravitationale.<\/span><\/div>\n
            De aceea sarcinile elctrice se mai numesc uneori si <\/span>mase electricei, <\/span><\/i>dar aceasta denumire tinde sa fie parasita.<\/span><\/div>\n
            Din acelasi motiv, tot asa cum fortele gravitationale se mai numesc si <\/span>newtoniene<\/span><\/i>, vom numi <\/span>coulombiene<\/span><\/i> fortele de interactiune electrica.<\/span><\/div>\n
\n<\/div>\n
                        In concluzie : <\/span>fortele coulombiene, ce apar intre doua corpuri electrizate, sunt direct proportionale cu produsu sarcinilor electrice si invers proportionale cu patratul distantei care le separa.<\/span><\/i><\/div>\n
            Intensitatea acestor forte scade, cand creste permitivitatea mdiului dielectric.<\/span><\/div>\n
\n<\/div>\n
            Experientele lui Coulomb, care au dus la formularea legii, repetate chiar si in conditiile de astazi, duc la rezultate destul de neprecise, fiindca fortele e masurat sunt foarte mici.<\/span><\/div>\n
            Ele au mai mult o importanta istorica si de aceea este preferabil sa consideram aceasta lege doar ca o ipoteza fundamentala si sa o verificam indirect, prin consecintele ei.<\/span><\/div>\n
\n<\/div>\n
<\/div>","protected":false},"excerpt":{"rendered":"

OBIECTUL ELECTROSTATICII .Putem constata experimental ca unele corpuri, de pilda rasina, ebonita, ceara rosie sau sticla capata insusirea sa atraga obiecte usoare : fulgi de pasare, fire de bumbac sau bucatele de hartie, dupa ce le frecam cu o stofa de lana, cu o blana sau cu o bucata de matase. Aceasta insusire dispare destul […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[1],"tags":[],"aioseo_notices":[],"yoast_head":"\nELECTROSTATICA FENOMENE FUNDAMENTALE - Jobs\/ Internships\/ Scholarships\/<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/rubyskynews.com\/index.php\/2011\/03\/30\/electrostatica-fenomene-fundamentale-2\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"ELECTROSTATICA FENOMENE FUNDAMENTALE - Jobs\/ Internships\/ Scholarships\/\" \/>\n<meta property=\"og:description\" content=\"OBIECTUL ELECTROSTATICII .Putem constata experimental ca unele corpuri, de pilda rasina, ebonita, ceara rosie sau sticla capata insusirea sa atraga obiecte usoare : fulgi de pasare, fire de bumbac sau bucatele de hartie, dupa ce le frecam cu o stofa de lana, cu o blana sau cu o bucata de matase. 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