{"id":3788,"date":"2018-02-15T10:14:08","date_gmt":"2018-02-15T10:14:08","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=3788"},"modified":"2024-08-20T16:07:09","modified_gmt":"2024-08-20T16:07:09","slug":"resolucao-comentada-eletrodinamica-primeira-e-segunda-lei-de-ohm","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/enem\/eletrodinamica-primeira-e-segunda-lei-de-ohm\/resolucao-comentada-eletrodinamica-primeira-e-segunda-lei-de-ohm\/","title":{"rendered":"Eletrodin\u00e2mica – Primeira e Segunda lei de Ohm – Resolu\u00e7\u00e3o"},"content":{"rendered":"

Resolu\u00e7\u00e3o Comentada<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Eletrodin\u00e2mica<\/span><\/span><\/span><\/p>\n

Primeira e Segunda lei de Ohm<\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

01-(ENEM-MEC)<\/b><\/span><\/span><\/span><\/p>\n

Baseado nas\u00a0 figuras:<\/b><\/span><\/span><\/span><\/p>\n

(1) Mantendo-se a sec\u00e7\u00e3o transversal constante e dobrando-se o comprimento (\u2113) do fi o, a resist\u00eancia (R) dobra\u00a0 —\u00a0 ent\u00e3o, a proporcionalidade entre \u2113 e R \u00e9 direta.<\/b><\/span><\/span><\/span><\/p>\n

(2) Mantendo-se o comprimento constante e dobrando-se a \u00e1rea da sec\u00e7\u00e3o transversal (A), a resist\u00eancia (R) fica dividida por dois\u00a0 —\u00a0 ent\u00e3o, a proporcionalidade entre A e R \u00e9 inversa.<\/b><\/span><\/span><\/span><\/p>\n

(3) Mantendo-se a resist\u00eancia constante e dobrando-se o comprimento (\u2113) do fio, a \u00e1rea da sec\u00e7\u00e3o transversal (A)<\/b><\/span><\/span><\/span><\/p>\n

dobra. Assim, a proporcionalidade entre \u2113 e A \u00e9 direta.<\/b><\/span><\/span><\/span><\/p>\n

R- C<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

02-UNESP-SP)<\/b><\/span><\/span><\/span><\/p>\n

Para i=2 A\u00a0 —\u00a0 U=5.i2=5.22=5.4\u00a0 —\u00a0 U=20V\u00a0 —\u00a0 R=U\/i=20\/2\u00a0 —\u00a0 R=5 \u2126\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>R- A<\/b><\/span><\/span><\/span><\/p>\n

03-(UFG-GO)<\/b><\/span><\/span><\/span><\/p>\n

\u00a0R=U\/i\u00a0 —\u00a0 1.500=220\/i\u00a0 —\u00a0 i=220\/1.500\u00a0 —\u00a0 i=0,1466 A\u00a0 —\u00a0 i=146,6mA\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>R- D<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

04-(UFMS-MS)\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Verifique teoria a seguir:\u00a0<\/b><\/span><\/span><\/span>Primeira lei de Ohm<\/b><\/span><\/span><\/span>\u00a0\u2013 Se a resist\u00eancia el\u00e9trica de um resistor for constante, a diferen\u00e7a de potencial aplicada nos seus extremos \u00e9 diretamente proporcional \u00e0 intensidade da corrente el\u00e9trica, ou seja,U<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\/i<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>=U<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\/i<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>= . . . =U\/i=constante. Nesse caso eles s\u00e3o chamados de\u00a0<\/b><\/span><\/span><\/span>resistores (ou condutores) \u00f4hmicos<\/b><\/span><\/span><\/span>\u00a0e, como a rela\u00e7\u00e3o R=U\/i \u00e9 uma fun\u00e7\u00e3o do primeiro grau o gr\u00e1fico U x i tem o aspecto do gr\u00e1fico da esquerda da figura abaixo:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Qualquer gr\u00e1fico U x i diferente do gr\u00e1fico da esquerda da figura acima n\u00e3o representa um resistor \u00f4hmico, como por exemplo, o gr\u00e1fico da direita.<\/b><\/span><\/span><\/span><\/p>\n

I- Falsa<\/b><\/span><\/span><\/span><\/p>\n

II- Verdadeira<\/b><\/span><\/span><\/span><\/p>\n

III- Falsa \u2013 veja c\u00e1lculos abaixo<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

R<\/b><\/span><\/span><\/span>III<\/b><\/span><\/span><\/sub><\/span>=U\/i=4\/8=0,5\u2126\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>IV<\/b><\/span><\/span><\/sub><\/span>=U\/i=4\/4=1\u2126<\/b><\/span><\/span><\/span><\/p>\n

\u00a0IV- Falsa \u2013 o condutor V n\u00e3o \u00e9 \u00f4hmico<\/b><\/span><\/span><\/span><\/p>\n

V Falsa \u2013 acima de 1V, a resist\u00eancia de I \u00e9 a menor de todas as \u00f4hmicas<\/b><\/span><\/span><\/span><\/p>\n

R- A.<\/b><\/span><\/span><\/span><\/p>\n

05-(CEFET-SC)<\/b><\/span><\/span><\/span><\/p>\n

O chuveiro deve dissipar a mesma pot\u00eancia nos dois estados\u00a0 —\u00a0 P=U2\/R\u00a0 —\u00a0 PSC=PPR\u00a0 —\u00a0 \u00a0USC2\/RSC= UPR2\/RPR\u00a0 —\u00a0 USC=2UP\u00adR\u00a0\u00a0—\u00a0 (2UPR)2\/RSC= UPR2\/RPR\u00ad\u00a0 —\u00a0 4UPR2\/RSC= UPR2\/RPR\u00a0 —\u00a0\u00a0RPR=RSC\/4\u00a0 —\u00a0 <\/b><\/span><\/span><\/span>R- C<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

06-(PUC-MG)<\/b><\/span><\/span><\/span><\/p>\n

\u00c1gua morna \u2013 m\u00e9dia pot\u00eancia \u2013 resist\u00eancia m\u00e9dia\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>R- A<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

07-(UFAL-AL)<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Dados\u00a0 —\u00a0 U = 600 V\u00a0 —\u00a0\u00a0 R1\u00a0= 2 k\u03a9 = 2.103\u00a0\u03a9\u00a0 —\u00a0 R2\u00a0= 16 k\u03a9 = 16.103\u00a0\u03a9\u00a0 —\u00a0 ao segurar as extremidades do peixe, a pessoa e o peixe se associam como resistores em s\u00e9rie\u00a0 —\u00a0 aplicando a 1\u00aa lei de Ohm\u00a0 —\u00a0 U = (R1\u00a0+ R2) i\u00a0 —\u00a0 600 = 18 .10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0i \u00a0—\u00a0 i = 600\/18.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 i=33,3.10<\/b><\/span><\/span><\/span>-3<\/b><\/span><\/span><\/sup><\/span>\u00a0A\u00a0 —\u00a0 i=33,3mA\u00a0 —\u00a0 19 mA < i < 100 mA\u00a0 <\/b><\/span><\/span><\/span>—\u00a0\u00a0\u00a0R- D<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

08-(FUVEST-SP)\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Observe o gr\u00e1fico abaixo onde foram escolhidos dois pontos A e B:\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

I. Falsa\u00a0 —\u00a0 quando a resist\u00eancia \u00e9 constante, tens\u00e3o e corrente s\u00e3o diretamente proporcionais, portanto o gr\u00e1fico \u00e9 uma reta que passa pela origem.<\/b><\/span><\/span><\/span><\/p>\n

II. Falsa\u00a0 —\u00a0 Calculando a resist\u00eancia para os pontos, A e B, destacados na figura\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>=U<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>\/i<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>=2\/0,15\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>=13,3\u03a9\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>=U<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>\/i<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>=6\/0,25\u00a0 —\u00a0 R<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>=24\u03a9\u00a0 —\u00a0 a resist\u00eancia aumenta com o aumento da corrente.<\/b><\/span><\/span><\/span><\/p>\n

III. Correta\u00a0 —\u00a0 \u00a0pot\u00eancias dissipadas para os valores dos pontos destacados\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>\u00a0= U<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>. i<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>\u00a0= 2.(0,15) = 0,3 W\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>=U<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>.i<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>=6.0,24=1,5W\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>\u00a0> P<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>\u00a0 — \u00a0a pot\u00eancia dissipada no filamento aumenta com o aumento da tens\u00e3o aplicada.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

R- C<\/b><\/span><\/span><\/span><\/p>\n

09-(PUC-MG)<\/b><\/span><\/span><\/span><\/p>\n

Dados\u00a0 — \u00a0D = 2 cm = 2.10<\/b><\/span><\/span><\/span>-2<\/b><\/span><\/span><\/sup><\/span>\u00a0m\u00a0 —\u00a0 L = 2.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0m\u00a0 —\u00a0\u00a0 i = 10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0A;\u00a0 —\u00a0 \u00a0\u0394t = 1 h = 3,6.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0s.<\/b><\/span><\/span><\/span><\/p>\n

A resist\u00eancia da linha \u00e9 dada pela 2\u00aa lei de Ohm\u00a0 — \u00a0R=\u03c1L\/S\u00a0 —\u00a0 \u00a0\u00e1rea da sec\u00e7\u00e3o transversal\u00a0 —\u00a0\u00a0 S= \u03c0r<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0=\u03c0(D\/2)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0—\u00a0 S=\u03c0D<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\/4\u00a0 —<\/b><\/span><\/span><\/span><\/p>\n

R=\u03c1L\/S=4\u03c1L\/(\u03c0D<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\/4)=4(1,57.10<\/b><\/span><\/span><\/span>-8<\/b><\/span><\/span><\/sup><\/span>).(2.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>)\/3,14.(2.10<\/b><\/span><\/span><\/span>-2<\/b><\/span><\/span><\/sup><\/span>)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 R=0,1\u03a9\u00a0\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=R.i<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=\u0394W\/\u0394t\u00a0 —\u00a0 \u0394W=P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>.\u0394t\u00a0 —\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\u0394W=R.i<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.\u0394t\u00a0 —\u00a0 \u0394W=0,1.(10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>.3,6.10<\/b><\/span><\/span><\/span>3<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 \u0394W=3,6.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>J.<\/b><\/span><\/span><\/span><\/p>\n

R- A<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

10-(UNIFESP-SP)<\/b><\/span><\/span><\/span><\/p>\n

C\u00e1lculo da resist\u00eancia el\u00e9trica de cada fio\u00a0 —\u00a0 segunda lei de Ohm\u00a0 —\u00a0 \u00a0R=\u03c1L\/S=1,6.10<\/b><\/span><\/span><\/span>-8<\/b><\/span><\/span><\/sup><\/span>.10\/4.10<\/b><\/span><\/span><\/span>-6<\/b><\/span><\/span><\/sup><\/span>=1,6.10<\/b><\/span><\/span><\/span>-7<\/b><\/span><\/span><\/sup><\/span>\/<\/b><\/span><\/span><\/span><\/p>\n

4.10<\/b><\/span><\/span><\/span>-6<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 R=0,4.10<\/b><\/span><\/span><\/span>-1<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>R=0,04\u2126\u00a0\u00a0<\/b><\/span><\/span><\/span>—\u00a0 corrente que chega \u00e0 resid\u00eancia\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=i.U\u00a0 —\u00a0 3.300=i.110\u00a0 —\u00a0 i=30 A\u00a0 —\u00a0 da caixa de rel\u00f3gio at\u00e9 a resid\u00eancia existem dois fios\u00a0 —\u00a0 R=2.0,04=8.10<\/b><\/span><\/span><\/span>-2<\/b><\/span><\/span><\/sup><\/span>\u2126\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=R.i<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>=8.10<\/b><\/span><\/span><\/span>-2<\/b><\/span><\/span><\/sup><\/span>.900\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=72W\u00a0 —\u00a0 R- D<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

11-(UDESC-SC)<\/b><\/span><\/span><\/span><\/p>\n

Sendo R=\u03c1.L\/S, pela tabela, o fio que possui menor resist\u00eancia el\u00e9trica \u00e9 o fio A\u00a0 —\u00a0 observe na express\u00e3o a seguir que, quanto maior a quantidade de energia consumida (W), maior ser\u00e1 a pot\u00eancia dissipada (P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>) no fio<\/b><\/span><\/span><\/span>\u00a0 —\u00a0\u00a0W=Po.\u0394t\u00a0 —\u00a0 observe tamb\u00e9m na express\u00e3o a seguir que\u00a0 a pot\u00eancia el\u00e9trica dissipada no fio \u00e9 inversamente proporcional \u00e0 sua resist\u00eancia el\u00e9trica R\u00a0 —\u00a0 Po=(U<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\/R).\u0394t\u00a0 —\u00a0 maior pot\u00eancia, menor resist\u00eancia, consome mais energia\u00a0 —\u00a0 menor resist\u00eancia \u2013 substituindo os valores de cada alternativa na equa\u00e7\u00e3o R=\u03c1.L\/S, chega-se \u00e0 resposta\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>R- C<\/b><\/span><\/span><\/span><\/p>\n

\u00a0<\/span><\/p>\n

12-(UDESC-SC)<\/b><\/span><\/span><\/span><\/p>\n

\u00a0I- Correta\u00a0 —\u00a0 P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>=R.i<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 —\u00a0 quanto maior i, maior P<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span><\/p>\n

II- Correta\u00a0 —\u00a0 R=\u03c1L\/S\u00a0 —\u00a0 quanto maior \u03c1, maior R e menor i<\/b><\/span><\/span><\/span><\/p>\n

III- Falsa\u00a0 —\u00a0 \u00e9 a raz\u00e3o U\/i que \u00e9 constante e n\u00e3o o produto U.i<\/b><\/span><\/span><\/span><\/p>\n

IV- Correta\u00a0 —\u00a0 Falsa\u00a0 —\u00a0 depende do tipo de associa\u00e7\u00e3o (s\u00e9rie, paralelo ou mista)<\/b><\/span><\/span><\/span><\/p>\n

R- D<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Voltar para os exerc\u00edcios<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

Resolu\u00e7\u00e3o Comentada Eletrodin\u00e2mica Primeira e Segunda lei de Ohm \u00a0 01-(ENEM-MEC) Baseado nas\u00a0 figuras: (1) Mantendo-se a sec\u00e7\u00e3o transversal constante e dobrando-se o comprimento (\u2113) do fi o, a resist\u00eancia (R) dobra\u00a0 —\u00a0 ent\u00e3o, a proporcionalidade entre \u2113 e R \u00e9 direta. (2) Mantendo-se o comprimento constante e dobrando-se a \u00e1rea da sec\u00e7\u00e3o transversal (A), a resist\u00eancia (R) fica dividida<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3786,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"class_list":["post-3788","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3788","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/comments?post=3788"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3788\/revisions"}],"predecessor-version":[{"id":10636,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3788\/revisions\/10636"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3786"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=3788"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}