{"id":5615,"date":"2020-11-09T03:26:23","date_gmt":"2020-11-09T03:26:23","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=5615"},"modified":"2024-06-26T14:22:26","modified_gmt":"2024-06-26T14:22:26","slug":"enem-2020-eletrodinamica","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/enem\/enem-2020-eletrodinamica\/","title":{"rendered":"ENEM – 2020 – ELETRODIN\u00c2MICA"},"content":{"rendered":"

ELETRICIDADE<\/b><\/span><\/span><\/span><\/p>\n

ELETRODIN\u00c2MICA<\/b><\/span><\/span><\/span><\/p>\n

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01-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-018)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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02-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-018)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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03- <\/b><\/span><\/span><\/span>(ENEM-MEC-019)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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Uma casa tem um cabo el\u00e9trico mal dimensionado,<\/b><\/span><\/span>\u00a0de\u00a0<\/b><\/span><\/span>resist\u00eancia igual a 10 \u2126<\/b><\/span><\/span>, que a\u00a0<\/b><\/span><\/span>conecta \u00e0 rede el\u00e9trica de 120 V.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Nessa casa, cinco l\u00e2mpadas,\u00a0<\/b><\/span><\/span>de\u00a0<\/b><\/span><\/span>resist\u00eancia igual a 200 \u2126,<\/b><\/span><\/span>\u00a0est\u00e3o\u00a0<\/b><\/span><\/span>conectadas ao mesmo circuito que uma televis\u00e3o de resist\u00eancia igual a 50 \u2126,<\/b><\/span><\/span>\u00a0conforme ilustrado no esquema.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>televis\u00e3o funciona apenas com tens\u00e3o entre 90 V e 130 V.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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O\u00a0<\/b><\/span><\/span>n\u00famero m\u00e1ximo de l\u00e2mpadas que podem ser ligadas sem que a televis\u00e3o pare de funcionar<\/b><\/span><\/span>\u00a0\u00e9:<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Observe<\/b><\/span><\/span>\u00a0no\u00a0<\/b><\/span><\/span>circuito fornecido\u00a0<\/b><\/span><\/span>que,\u00a0<\/b><\/span><\/span>para que a televis\u00e3o de 50 \u2126 funcione fornecendo o n\u00famero m\u00e1ximo de l\u00e2mpadas ligadas e associadas em paralelo<\/b><\/span><\/span>\u00a0essa TV\u00a0<\/b><\/span><\/span>dever\u00e1 estar submetida \u00e0 menor tens\u00e3o compreendida entre 90 v e 130 V, que \u00e9 de 90 V.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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

04-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-019)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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As\u00a0<\/b><\/span><\/span>redes de alta tens\u00e3o para transmiss\u00e3o de energia el\u00e9trica geram campo magn\u00e9tico vari\u00e1vel<\/b><\/span><\/span>\u00a0o\u00a0<\/b><\/span><\/span>suficiente para induzir corrente el\u00e9trica no arame das cercas.\u00a0<\/b><\/span><\/span>Tanto os\u00a0<\/b><\/span><\/span>animais quanto os funcion\u00e1rios das propriedades rurais ou das concession\u00e1rias de energia devem ter muito cuidado ao se aproximarem de uma cerca quando esta estiver pr\u00f3xima a uma rede de alta tens\u00e3o,<\/b><\/span><\/span>\u00a0pois, se\u00a0<\/b><\/span><\/span>tocarem no arame da cerca, poder\u00e3o sofrer choque el\u00e9trico.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Para\u00a0<\/b><\/span><\/span>minimizar este tipo de problema,<\/b><\/span><\/span>\u00a0deve-se:<\/b><\/span><\/span><\/span><\/span><\/p>\n

(A)<\/b><\/span><\/span>\u00a0Fazer o aterramento dos arames da cerca.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(B)\u00a0<\/b><\/span><\/span>Acrescentar fus\u00edvel de seguran\u00e7a na cerca.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(C)\u00a0<\/b><\/span><\/span>Realizar o aterramento da rede de alta tens\u00e3o.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(D)\u00a0<\/b><\/span><\/span>Instalar fus\u00edvel de seguran\u00e7a na rede de alta tens\u00e3o.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(E)\u00a0<\/b><\/span><\/span>Utilizar fios encapados com isolante na rede de alta tens\u00e3o.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Quando voc\u00ea\u00a0<\/b><\/span><\/span>encosta as m\u00e3os no arame percorrido por corrente el\u00e9trica,\u00a0<\/b><\/span><\/span>essa corrente,\u00a0<\/b><\/span><\/span>devido \u00e0 diferen\u00e7a de potencial entre o arame e o solo em contato com seus p\u00e9s, \u00e9 desviada pelo seu corpo fazendo-o funcionar como<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>condutor el\u00e9trico \u201cfio terra\u201d.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Essa\u00a0<\/b><\/span><\/span>passagem de corrente el\u00e9trica pelo seu corpo\u00a0<\/b><\/span><\/span>\u00e9 o\u00a0<\/b><\/span><\/span>choque el\u00e9trico.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Assim,\u00a0<\/b><\/span><\/span>ligando um \u201cfio terra\u201d entre a cerca e o solo (fazendo um aterramento)\u00a0<\/b><\/span><\/span>voc\u00ea estar\u00e1\u00a0<\/b><\/span><\/span>minimizando o risco desse choque el\u00e9trico.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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

05-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-017)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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Dispositivos eletr\u00f4nicos<\/b><\/span><\/span>\u00a0que\u00a0<\/b><\/span><\/span>utilizam materiais de baixo custo,\u00a0<\/b><\/span><\/span>como\u00a0<\/b><\/span><\/span>pol\u00edmeros semicondutores,<\/b><\/span><\/span>\u00a0t\u00eam<\/b><\/span><\/span><\/span><\/span><\/p>\n

sido\u00a0<\/b><\/span><\/span>desenvolvidos para monitorar a concentra\u00e7\u00e3o de am\u00f4nia\u00a0<\/b><\/span><\/span>(g\u00e1s t\u00f3xico e incolor) em\u00a0<\/b><\/span><\/span>granjas av\u00edcolas.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>polianilina \u00e9 um pol\u00edmero semicondutor\u00a0<\/b><\/span><\/span>que tem o\u00a0<\/b><\/span><\/span>valor de sua resist\u00eancia el\u00e9trica nominal quadruplicado quando exposta a altas concentra\u00e7\u00f5es de am\u00f4nia.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Na\u00a0<\/b><\/span><\/span>aus\u00eancia de am\u00f4nia,<\/b><\/span><\/span>\u00a0a\u00a0<\/b><\/span><\/span>polianilina\u00a0<\/b><\/span><\/span>se\u00a0<\/b><\/span><\/span>comporta como um resistor \u00f4hmico\u00a0<\/b><\/span><\/span>e a\u00a0<\/b><\/span><\/span>sua resposta el\u00e9trica \u00e9 mostrada no gr\u00e1fico.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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O\u00a0<\/b><\/span><\/span>valor da resist\u00eancia el\u00e9trica da polianilina\u00a0<\/b><\/span><\/span>na presen\u00e7a de\u00a0<\/b><\/span><\/span>altas concentra\u00e7\u00f5es de am\u00f4nia,<\/b><\/span><\/span>\u00a0em\u00a0<\/b><\/span><\/span>ohm, \u00e9 igual a<\/b><\/span><\/span><\/span><\/span><\/p>\n

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06-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-017)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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Vamos\u00a0<\/b><\/span><\/span>analisar apenas a parte inferior do circuito<\/b><\/span><\/span>\u00a0onde\u00a0<\/b><\/span><\/span>circulam as correntes i, i1\u00a0e i2,\u00a0<\/b><\/span><\/span>j\u00e1 que com<\/b><\/span><\/span><\/span><\/span><\/p>\n

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apenas esses dados \u00e9 poss\u00edvel calcular a tens\u00e3o U pedida.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Observe que o\u00a0<\/b><\/span><\/span>trecho que possui o resistor de R2\u00a0= 120 \u2126 \u00e9 percorrido pela corrente i2\u00a0= 500 mA = 0,5 A (corrente nominal suportada pelo fus\u00edvel).<\/b><\/span><\/span><\/span><\/span><\/p>\n

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07-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-017)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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No\u00a0<\/b><\/span><\/span>manual fornecido pelo fabricante\u00a0<\/b><\/span><\/span>de uma\u00a0<\/b><\/span><\/span>ducha el\u00e9trica de 220V\u00a0<\/b><\/span><\/span>\u00e9\u00a0<\/b><\/span><\/span>apresentado um gr\u00e1fico\u00a0<\/b><\/span><\/span>com a\u00a0<\/b><\/span><\/span>varia\u00e7\u00e3o da temperatura da \u00e1gua em fun\u00e7\u00e3o da vaz\u00e3o para tr\u00eas condi\u00e7\u00f5es\u00a0<\/b><\/span><\/span>(morno, quente e superquente).<\/b><\/span><\/span><\/span><\/span><\/p>\n

Na\u00a0<\/b><\/span><\/span>condi\u00e7\u00e3o\u00a0superquente,\u00a0<\/b><\/span><\/span>a\u00a0<\/b><\/span><\/span>pot\u00eancia dissipada \u00e9 de 6500 W.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Considere o\u00a0<\/b><\/span><\/span>calor espec\u00edfico da \u00e1gua igual a 4200 J\/(kg C)\u00a0<\/b><\/span><\/span>e a\u00a0<\/b><\/span><\/span>densidade da \u00e1gua igual a 1 kg\/L.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Com\u00a0<\/b><\/span><\/span>base nas informa\u00e7\u00f5es dadas,\u00a0<\/b><\/span><\/span>a\u00a0<\/b><\/span><\/span>pot\u00eancia na condi\u00e7\u00e3o morno corresponde a que fra\u00e7\u00e3o da pot\u00eancia na condi\u00e7\u00e3o superquente?<\/b><\/span><\/span><\/span><\/span><\/p>\n

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A\u00a0<\/b><\/span><\/span>resist\u00eancia el\u00e9trica do chuveiro,\u00a0<\/b><\/span><\/span>quando aquecida,\u00a0<\/b><\/span><\/span>transforma integralmente energia el\u00e9trica (Wel\u00e9trica)\u00a0<\/b><\/span><\/span>em\u00a0<\/b><\/span><\/span>energia t\u00e9rmica (calor Q)\u00a0Wel\u00e9trica\u00a0= Q.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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08-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-017)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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Veja na\u00a0<\/b><\/span><\/span>figura e no esquema abaix<\/b><\/span><\/span>o onde\u00a0<\/b><\/span><\/span>E = 10 000 V\u00a0<\/b><\/span><\/span>\u00e9 a\u00a0<\/b><\/span><\/span>for\u00e7a eletromotriz\u00a0<\/b><\/span><\/span>do gerador,\u00a0<\/b><\/span><\/span>r\u00a0<\/b><\/span><\/span>sua\u00a0<\/b><\/span><\/span>resist\u00eancia interna, Rh\u00a0= 1 000<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>\u2126\u00a0<\/b><\/span><\/span>\u00e9 a\u00a0<\/b><\/span><\/span>resist\u00eancia corporal da pessoa e i = 0,01 A \u00e9 a m\u00e1xima corrente n\u00e3o letal atrav\u00e9s do corpo da pessoa.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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ELETROMAGNETISMO<\/b><\/span><\/span><\/span><\/p>\n

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09-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-019)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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O\u00a0<\/b><\/span><\/span>espectr\u00f4metro de massa de tempo de voo \u00e9 um dispositivo utilizado para medir a massa de \u00edons<\/b><\/span><\/span>. Nele,\u00a0<\/b><\/span><\/span>um \u00edon de carga el\u00e9trica q \u00e9 lan\u00e7ado em uma regi\u00e3o de campo magn\u00e9tico constante B, descrevendo uma trajet\u00f3ria helicoidal,<\/b><\/span><\/span>\u00a0conforme a figura.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Essa trajet\u00f3ria \u00e9 formada pela composi\u00e7\u00e3o de um movimento circular uniforme no plano yz e uma transla\u00e7\u00e3o ao longo do eixo x.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>vantagem desse dispositivo \u00e9 que a velocidade angular do movimento helicoidal do \u00edon \u00e9 independente de sua velocidade inicial.<\/b><\/span><\/span><\/span><\/span><\/p>\n

O\u00a0<\/b><\/span><\/span>dispositivo ent\u00e3o mede o tempo t de voo para N voltas do \u00edon.\u00a0<\/b><\/span><\/span>Logo, com\u00a0<\/b><\/span><\/span>base nos valores q, B, N e t, pode-se determinar a massa do \u00edon.\u00a0<\/b><\/span><\/span>A\u00a0<\/b><\/span><\/span>massa do \u00edon medida por esse dispositivo\u00a0<\/b><\/span><\/span>ser\u00e1<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Se voc\u00ea n\u00e3o domina a teoria ela est\u00e1 a seguir:<\/b><\/span><\/span><\/span><\/span><\/p>\n

Carga q lan\u00e7ada obliquamente no interior de um campo magn\u00e9tico uniforme<\/b><\/span><\/span><\/span><\/span><\/p>\n

\"ELETRODIN\u00c2MICA\"<\/p>\n

Analisando o exerc\u00edcio com base apenas na componente paralela ao movimento que produz um movimento circular uniforme como resumo fornecido abaixo:<\/b><\/span><\/span><\/span><\/span><\/p>\n

Carga el\u00e9trica\u00a0q\u00a0lan\u00e7ada com velocidade\u00a0\u00a0lan\u00e7ada perpendicularmente \u00e0s linhas de indu\u00e7\u00e3o de um campo magn\u00e9tico uniforme<\/b><\/span><\/span><\/span><\/span><\/p>\n

Observe que,\u00a0<\/b><\/span><\/span>neste caso<\/b><\/span><\/span>\u00a0o \u00e2ngulo entre\u00a0\u00a0e\u00a0\u00a0\u00e9\u00a0<\/b><\/span><\/span>90o\u00a0(s\u00e3o perpendiculares) e que sen90o\u00a0= 1.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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

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10-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-017)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

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Para\u00a0<\/b><\/span><\/span>demonstrar o processo de transforma\u00e7\u00e3o de energia mec\u00e2nica em el\u00e9trica,\u00a0<\/b><\/span><\/span>um\u00a0<\/b><\/span><\/span>estudante constr\u00f3i um pequeno gerador utilizando:<\/b><\/span><\/span><\/span><\/span><\/p>\n

\u00a0um\u00a0<\/b><\/span><\/span>fio de cobre de di\u00e2metro D enrolado em N espiras circulares de \u00e1rea A;<\/b><\/span><\/span><\/span><\/span><\/p>\n

\u00a0dois\u00a0<\/b><\/span><\/span>\u00edm\u00e3s que criam no espa\u00e7o entre eles um campo magn\u00e9tico uniforme de intensidade B;\u00a0<\/b><\/span><\/span>e<\/b><\/span><\/span><\/span><\/p>\n

\u00a0um\u00a0<\/b><\/span><\/span>sistema de engrenagens\u00a0<\/b><\/span><\/span>que lhe permite\u00a0<\/b><\/span>girar as espiras em torno de um eixo\u00a0<\/b><\/span><\/span>com uma\u00a0<\/b><\/span>frequ\u00eancia f.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Ao\u00a0<\/b><\/span><\/span>fazer<\/b><\/span><\/span>\u00a0o\u00a0<\/b><\/span><\/span>gerador funcionar,<\/b><\/span><\/span>\u00a0o\u00a0<\/b><\/span><\/span>estudante obteve uma tens\u00e3o m\u00e1xima V\u00a0<\/b><\/span><\/span>e uma\u00a0<\/b><\/span><\/span>corrente de curto-circuito i.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Para dobrar o valor da tens\u00e3o m\u00e1xima V do gerador mantendo constante o valor da corrente de curto i, o estudante deve dobrar o(a)<\/b><\/span><\/span><\/span><\/span><\/p>\n

(a)\u00a0<\/b><\/span><\/span>n\u00famero de espiras.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(b)\u00a0<\/b><\/span><\/span>frequ\u00eancia de giro.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(c)\u00a0<\/b><\/span><\/span>intensidade do campo magn\u00e9tico.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(d)\u00a0<\/b><\/span><\/span>\u00e1rea das espiras.<\/b><\/span><\/span><\/span><\/span><\/p>\n

(e)\u00a0<\/b><\/span><\/span>di\u00e2metro do fio.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Se, ao\u00a0<\/b><\/span><\/span>fazer<\/b><\/span><\/span>\u00a0o\u00a0<\/b><\/span><\/span>gerador funcionar,<\/b><\/span><\/span>\u00a0o\u00a0<\/b><\/span><\/span>estudante obteve uma tens\u00e3o m\u00e1xima V\u00a0<\/b><\/span><\/span>e uma\u00a0<\/b><\/span><\/span>corrente de curto-circuito i, ent\u00e3o a tens\u00e3o m\u00e1xima U \u00e9 a for\u00e7a eletromotriz induzida\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>do gerador, ou seja, V =\u00a0.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Para\u00a0<\/b><\/span><\/span>n espiras a for\u00e7a eletromotriz induzida\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>\u00e9 fornecida por\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>=<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>n.\u00a0= n.\u00a0.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Para\u00a0<\/b><\/span><\/span>variar o fluxo magn\u00e9tico no interior da associa\u00e7\u00e3o de espiras, podemos mudar\u00a0<\/b><\/span><\/span>o\u00a0<\/b><\/span><\/span>valor do campo magn\u00e9tico (B), da \u00e1rea (S), do \u00e2ngulo de giro () ou o n\u00famero de espiras (n).<\/b><\/span><\/span><\/span><\/span><\/p>\n

Mas o\u00a0<\/b><\/span><\/span>enunciado pede tamb\u00e9m que, al\u00e9m de dobrar\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>deve-se\u00a0<\/b><\/span><\/span>manter constante\u00a0a corrente de\u00a0curto circuito\u00a0icc<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>que \u00e9 fornecida por\u00a0<\/b><\/span><\/span>icc\u00a0=\u00a0\u00a0,\u00a0<\/b><\/span><\/span>onde\u00a0<\/b><\/span><\/span>r \u00e9 a resist\u00eancia interna devida \u00e0s n espiras<\/b><\/span><\/span>, o que\u00a0<\/b><\/span><\/span>s\u00f3 pode acontecer se voc\u00ea dobrar r.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Mas, pela\u00a0<\/b><\/span><\/span>segunda lei de Ohm a resist\u00eancia r\u00a0<\/b><\/span><\/span>\u00e9 fornecida por:<\/b><\/span><\/span><\/span><\/span><\/p>\n

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Como o\u00a0<\/b><\/span><\/span>exerc\u00edcio<\/b><\/span><\/span>\u00a0pede\u00a0<\/b><\/span><\/span>o dobro da d.d.p. induzida, sem mudar a corrente de curto-circuito icc,\u00a0<\/b><\/span><\/span>al\u00e9m de\u00a0<\/b><\/span><\/span>dobrarmos o fluxo\u00a0,\u00a0<\/b><\/span><\/span>devemos\u00a0<\/b><\/span><\/span>dobrar tamb\u00e9m a resist\u00eancia r do material.\u00a0<\/b><\/span><\/span>Isso pode acontecer\u00a0<\/b><\/span><\/span>atrav\u00e9s da mudan\u00e7a do material\u00a0, do comprimento L ou da \u00e1rea S de se\u00e7\u00e3o do fio.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>\u00fanica op\u00e7\u00e3o que satisfaz\u00a0<\/b><\/span><\/span>as\u00a0<\/b><\/span><\/span>duas condi\u00e7\u00f5es ao mesmo tempo \u00e9 dobrar o n\u00famero n de espiras,\u00a0<\/b><\/span><\/span>o que\u00a0<\/b><\/span><\/span>dobra a d.d.p. e a resist\u00eancia do material ao mesmo tempo,\u00a0<\/b><\/span><\/span>e que mant\u00e9m\u00a0<\/b><\/span><\/span>a corrente de curto inalterada.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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

11-<\/b><\/span><\/span><\/span> <\/b>(ENEM-MEC-018)<\/b><\/span><\/span><\/span><\/span><\/span><\/p>\n

<\/p>\n

A\u00a0<\/b><\/span><\/span>tecnologia de comunica\u00e7\u00e3o\u00a0<\/b><\/span><\/span>da\u00a0<\/b><\/span><\/span>etiqueta RFID (chamada de etiqueta inteligente)<\/b><\/span><\/span>\u00a0\u00e9\u00a0<\/b><\/span><\/span>usada h\u00e1 anos para rastrear gado, vag\u00f5es de trem, bagagem a\u00e9rea e carros nos ped\u00e1gios.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Um modelo mais barato dessas etiquetas\u00a0<\/b><\/span><\/span>pode funcionar sem baterias e \u00e9 constitu\u00eddo por tr\u00eas componentes: um microprocessador de sil\u00edcio; uma bobina de metal, feita de cobre ou de alum\u00ednio, que \u00e9 enrolada em um padr\u00e3o circular; e um encapsulador, que \u00e9 um material de vidro ou pol\u00edmero envolvendo o microprocessador e a bobina.<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/span><\/p>\n

Na\u00a0<\/b><\/span><\/span>presen\u00e7a de um campo de radiofrequ\u00eancia gerado pelo leitor, a etiqueta transmite sinais.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>dist\u00e2ncia de leitura \u00e9 determinada pelo tamanho da bobina e pela pot\u00eancia da onda de r\u00e1dio emitida pelo leitor<\/b><\/span><\/span>.<\/b><\/span><\/span><\/span><\/span><\/p>\n

A\u00a0<\/b><\/span><\/span>etiqueta funciona sem pilhas porque o campo
\n(A)\u00a0<\/b><\/span><\/span>el\u00e9trico da onda de r\u00e1dio agita el\u00e9trons da bobina.
\n<\/b><\/span><\/span>(B)\u00a0<\/b><\/span><\/span>el\u00e9trico da onda de r\u00e1dio cria uma tens\u00e3o na bobina.
\n<\/b><\/span><\/span>(C)\u00a0<\/b><\/span><\/span>magn\u00e9tico da onda de r\u00e1dio induz corrente na bobina.
\n<\/b><\/span><\/span>(D)\u00a0<\/b><\/span><\/span>magn\u00e9tico da onda de r\u00e1dio aquece os fios da bobina.
\n<\/b><\/span><\/span>(E)\u00a0<\/b><\/span><\/span>magn\u00e9tico da onda de r\u00e1dio diminui a resson\u00e2ncia no interior da bobina<\/b><\/span><\/span>.<\/b><\/span><\/span><\/span><\/span><\/p>\n

O\u00a0<\/b><\/span><\/span>leitor da etiqueta emite um campo de radiofrequ\u00eancia<\/b><\/span><\/span>\u00a0(por meio de ondas magn\u00e9ticas de r\u00e1dio)\u00a0<\/b><\/span><\/span>\u00e0 etiqueta eletr\u00f4nica identificadora (tags) que retornam esses sinais de radiofrequ\u00eancia para os leitores.<\/b><\/span><\/span><\/span><\/span><\/p>\n

<\/p>\n

Os leitores<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>captam essas informa\u00e7\u00f5es quando o fluxo magn\u00e9tico vari\u00e1vel produzido no retorno dessas ondas faz surgir na bobina (espira) do leitor uma corrente el\u00e9trica induzida.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Pela\u00a0<\/b><\/span><\/span>Lei de Faraday essa corrente el\u00e9trica origina na bobina um campo magn\u00e9tico tamb\u00e9m vari\u00e1vel que \u00e9 detectado pelo leitor que registra essas informa\u00e7\u00f5es.<\/b><\/span><\/span><\/span><\/span><\/p>\n

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

 <\/p>\n

Clique aqui para ver sobre o tema!<\/a><\/p>\n

Confira as v\u00eddeo aulas!<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

ELETRICIDADE ELETRODIN\u00c2MICA   01- (ENEM-MEC-018) 02- (ENEM-MEC-018)   03- (ENEM-MEC-019) Uma casa tem um cabo el\u00e9trico mal dimensionado,\u00a0de\u00a0resist\u00eancia igual a 10 \u2126, que a\u00a0conecta \u00e0 rede el\u00e9trica de 120 V. Nessa casa, cinco l\u00e2mpadas,\u00a0de\u00a0resist\u00eancia igual a 200 \u2126,\u00a0est\u00e3o\u00a0conectadas ao mesmo circuito que uma televis\u00e3o de resist\u00eancia igual a 50 \u2126,\u00a0conforme ilustrado no esquema. A\u00a0televis\u00e3o funciona apenas com tens\u00e3o entre 90<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":3575,"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-5615","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/5615","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=5615"}],"version-history":[{"count":4,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/5615\/revisions"}],"predecessor-version":[{"id":9762,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/5615\/revisions\/9762"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/3575"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=5615"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}