{"id":2199,"date":"2016-05-14T23:30:20","date_gmt":"2016-05-14T23:30:20","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2199"},"modified":"2024-09-02T14:32:33","modified_gmt":"2024-09-02T14:32:33","slug":"reflexao-total","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/optica\/optica-geometrica\/reflexao-total\/","title":{"rendered":"Reflex\u00e3o Total"},"content":{"rendered":"

Reflex\u00e3o Total <\/b><\/span><\/span><\/span><\/p>\n

Reflex\u00e3o total \u2013 \u00c2ngulo Limite (L)<\/b><\/span><\/span><\/span><\/p>\n

Considere um <\/b><\/span><\/span><\/span>raio de luz se propagando de um meio menos refringente (ar,\u00a0n<\/b><\/span><\/span><\/span>ar <\/b><\/span><\/span><\/sub><\/span>= 1) <\/b><\/span><\/span><\/span>para um <\/b><\/span><\/span><\/span>meio mais refringente (\u00e1gua,\u00a0n<\/b><\/span><\/span><\/span>\u00e1gua <\/b><\/span><\/span><\/sub><\/span>= 1,33), <\/b><\/span><\/span><\/span>sendo<\/b><\/span><\/span><\/span> <\/b>i <\/b><\/span><\/span><\/span>o \u00e2ngulo de incid\u00eancia <\/b><\/span><\/span><\/span>e<\/b><\/span><\/span><\/span> <\/b>r<\/b><\/span><\/span><\/span> o \u00e2ngulo de refra\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

Nesse <\/b><\/span><\/span><\/span>caso o raio <\/b><\/span><\/span><\/span>refratado r<\/b><\/span><\/span><\/span> se aproxima da normal. <\/b><\/span><\/span><\/span>(Figura 1)<\/b><\/span><\/span><\/span><\/p>\n

Aumentando o \u00e2ngulo de incid\u00eancia para i\u2019, o \u00e2ngulo de refra\u00e7\u00e3o aumenta para r\u2019<\/b><\/span><\/span><\/span>. (Figura 2)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>m\u00e1ximo de aumento do \u00e2ngulo de incid\u00eancia ocorre <\/b><\/span><\/span><\/span>na figura 3, onde <\/b><\/span><\/span><\/span>i\u2019\u2019 = 90<\/b><\/span><\/span><\/span>o\u00a0<\/b><\/span><\/span><\/sup><\/span>e que <\/b><\/span><\/span><\/span>corresponder\u00e1 <\/b><\/span><\/span><\/span>a um <\/b><\/span><\/span><\/span>\u00e2ngulo de refra\u00e7\u00e3o r\u2019\u2019. <\/b><\/span><\/span><\/span><\/p>\n

Nesse caso, o <\/b><\/span><\/span><\/span>raio de luz incide praticamente paralelo \u00e0 superf\u00edcie da \u00e1gua <\/b><\/span><\/span><\/span>(incid\u00eancia rasante) e <\/b><\/span><\/span><\/span>n\u00e3o<\/b><\/span><\/span><\/span> <\/b>\u00e9 mais poss\u00edvel aument\u00e1-lo.<\/b><\/span><\/span><\/span><\/p>\n

Agora <\/b><\/span><\/span><\/span>vamos fazer o <\/b><\/span><\/span><\/span>caminho inverso, <\/b><\/span><\/span><\/span>ou seja, vamos <\/b><\/span><\/span><\/span>fazer a luz se refratar da \u00e1gua para o ar<\/b><\/span><\/span><\/span> <\/b>e pelo <\/b><\/span><\/span><\/span>princ\u00edpio da reversibilidade a luz percorre o mesmo caminho das figuras anteriores, s\u00f3 que no sentido inverso.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Verifique<\/b><\/span><\/span><\/span> na <\/b><\/span><\/span><\/span>figura 3 acima <\/b><\/span><\/span><\/span>que, quando <\/b><\/span><\/span><\/span>a luz incide na superf\u00edcie da \u00e1gua com \u00e2ngulo r\u2019\u2019<\/b><\/span><\/span><\/span>, ela se <\/b><\/span><\/span><\/span>refrata no ar praticamente paralelo \u00e0 superf\u00edcie da \u00e1gua <\/b><\/span><\/span><\/span>(emerg\u00eancia rasante). <\/b><\/span><\/span><\/span><\/p>\n

Nesse <\/b><\/span><\/span><\/span>caso espec\u00edfico, <\/b><\/span><\/span><\/span>denominamos r\u2019\u2019 de\u00a0<\/b><\/span><\/span><\/span>\u00e2ngulo limite L. <\/b><\/span><\/span><\/span>(Figura 1 abaixo)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>partir da\u00ed come\u00e7a o que denominamos de\u00a0<\/b><\/span><\/span><\/span>reflex\u00e3o total.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Para <\/b><\/span><\/span><\/span>qualquer \u00e2ngulo de incid\u00eancia <\/b><\/span><\/span><\/span>maior que o \u00e2ngulo limite L (i\u00a0>\u00a0L),<\/b><\/span><\/span><\/span> <\/b>o <\/b><\/span><\/span><\/span>raio de luz <\/b><\/span><\/span><\/span>sofre <\/b><\/span><\/span><\/span>reflex\u00e3o total ou reflex\u00e3o interna retornando \u00e0 \u00e1gua, <\/b><\/span><\/span><\/span>tal que i = r. <\/b><\/span><\/span><\/span>(Figuras 2 e 3 acima)<\/b><\/span><\/span><\/span><\/p>\n

C\u00e1lculo do \u00e2ngulo limite (L)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Condi\u00e7\u00f5es para que ocorra reflex\u00e3o total<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O que voc\u00ea deve saber, informa\u00e7\u00f5es e dicas<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"\u00a0A <\/b><\/span><\/span><\/span>reflex\u00e3o normal ou externa <\/b><\/span><\/span><\/span>\u00e9 sempre <\/b><\/span><\/span><\/span>acompanhada de refra\u00e7\u00e3o, <\/b><\/span><\/span><\/span>mas na\u00a0<\/b><\/span><\/span><\/span>reflex\u00e3o total ou interna nenhuma luz se refrata.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0A <\/b><\/span><\/span><\/span>luz<\/b><\/span><\/span><\/span> \u00e9 uma <\/b><\/span><\/span><\/span>onda eletromagn\u00e9tica <\/b><\/span><\/span><\/span>e suas <\/b><\/span><\/span><\/span>propriedades decorrem deste fato. <\/b><\/span><\/span><\/span><\/p>\n

Por\u00e9m existem <\/b><\/span><\/span><\/span>outros tipos de ondas eletromagn\u00e9ticas <\/b><\/span><\/span><\/span>que tamb\u00e9m <\/b><\/span><\/span><\/span>possuem<\/b><\/span><\/span><\/span> as <\/b><\/span><\/span><\/span>mesmas propriedades da luz <\/b><\/span><\/span><\/span>como, por exemplo, as <\/b><\/span><\/span><\/span>ondas de r\u00e1dio e a radia\u00e7\u00e3o infravermelha <\/b><\/span><\/span><\/span>(ou luz infravermelha) que <\/b><\/span><\/span><\/span>\u00e9 respons\u00e1vel pela sensa\u00e7\u00e3o de calor que sentimos quando estamos sob o Sol.<\/b><\/span><\/span><\/span><\/p>\n

\"\" O <\/b><\/span><\/span><\/span>\u00e2ngulo limite <\/b><\/span><\/span><\/span>pode ser <\/b><\/span><\/span><\/span>\u00e2ngulo de incid\u00eancia (fig. 1) ou \u00e2ngulo de refra\u00e7\u00e3o (fig. 2)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" A express\u00e3o do \u00e2ngulo limite tamb\u00e9m pode ser \"\" <\/b><\/span><\/span><\/span>sen L= n<\/b><\/span><\/span><\/span>menor<\/b><\/span><\/span><\/sub><\/span>\/n<\/b><\/span><\/span><\/span>maior<\/b><\/span><\/span><\/sub><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\" A <\/b><\/span><\/span><\/span>reflex\u00e3o total <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>muito usada na pr\u00e1tica, <\/b><\/span><\/span><\/span>para <\/b><\/span><\/span><\/span>substituir os espelhos<\/b><\/span><\/span><\/span> por <\/b><\/span><\/span><\/span>meios transparentes <\/b><\/span><\/span><\/span>(vidros ou cristais de <\/b><\/span><\/span><\/span>reflex\u00e3o total<\/b><\/span><\/span><\/span>) e nos <\/b><\/span><\/span><\/span>instrumentos \u00f3ticos.<\/b><\/span><\/span><\/span><\/p>\n

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

Fibras \u00f3pticas<\/b><\/span><\/span><\/span><\/p>\n

Usadas como <\/b><\/span><\/span><\/span>meio de transmiss\u00e3o <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>ondas eletromagn\u00e9ticas <\/b><\/span><\/span><\/span>(como a luz). <\/b><\/span><\/span><\/span><\/p>\n

Feitas de <\/b><\/span><\/span><\/span>pl\u00e1stico ou de vidro <\/b><\/span><\/span><\/span>e tem <\/b><\/span><\/span><\/span>di\u00e2metros vari\u00e1veis <\/b><\/span><\/span><\/span>(mais finos que um fio de cabelo at\u00e9 v\u00e1rios mil\u00edmetros).<\/b><\/span><\/span><\/span><\/p>\n

Em rela\u00e7\u00e3o aos <\/b><\/span><\/span><\/span>cabos met\u00e1licos de cobre <\/b><\/span><\/span><\/span>tem a <\/b><\/span><\/span><\/span>vantagem de serem imunes \u00e0s interfer\u00eancias eletromagn\u00e9ticas<\/b><\/span><\/span><\/span> al\u00e9m de <\/b><\/span><\/span><\/span>n\u00e3o serem afetados com problemas decorrentes\u00a0da eletricidade.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>luz se propaga no interior do n\u00facleo <\/b><\/span><\/span><\/span>num <\/b><\/span><\/span><\/span>caminho totalmente espelhado <\/b><\/span><\/span><\/span>devido ao <\/b><\/span><\/span><\/span>fen\u00f4meno da reflex\u00e3o total <\/b><\/span><\/span><\/span>que ocorrer\u00e1 no <\/b><\/span><\/span><\/span>interior do n\u00facleo <\/b><\/span><\/span><\/span>desde que <\/b><\/span><\/span><\/span>o \u00edndice de refra\u00e7\u00e3o do <\/b><\/span><\/span><\/span>n\u00facleo (n<\/b><\/span><\/span><\/span>n<\/b><\/span><\/span><\/sub><\/span>) seja<\/b><\/span><\/span><\/span> <\/b>maior que o \u00edndice de refra\u00e7\u00e3o da casca (n<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>)<\/b><\/span><\/span><\/span> <\/b>e que o <\/b><\/span><\/span><\/span>\u00e2ngulo de incid\u00eancia em rela\u00e7\u00e3o \u00e0 normal ao incidir na casca seja maior que o \u00e2ngulo limite L.<\/b><\/span><\/span><\/span><\/p>\n

Utilizados em <\/b><\/span><\/span><\/span>comunica\u00e7\u00f5es<\/b><\/span><\/span><\/span> (rede telef\u00f4nica, televis\u00e3o por cabo, distribui\u00e7\u00e3o de energia el\u00e9trica), em<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

medicina<\/b><\/span><\/span><\/span> (sistemas de monitora\u00e7\u00e3o interna do corpo humano e instrumenta\u00e7\u00e3o cir\u00fargica), etc. <\/b><\/span><\/span><\/span><\/p>\n

N\u00e3o importa a <\/b><\/span><\/span><\/span>dist\u00e2ncia, levam a informa\u00e7\u00e3o quase instantaneamente, ou seja, \u00e0 velocidade pr\u00f3xima \u00e0 da luz.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

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

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

Devido \u00e0 <\/b><\/span><\/span><\/span>varia\u00e7\u00e3o da densidade do ar com a temperatura<\/b><\/span><\/span><\/span>, temos a <\/b><\/span><\/span><\/span>ilus\u00e3o em dias quentes e secos<\/b><\/span><\/span><\/span>, de <\/b><\/span><\/span><\/span>po\u00e7as de \u00e1gua, imagens de carros, de nuvens, etc., <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>miragens em desertos,<\/b><\/span><\/span><\/span> pois o <\/b><\/span><\/span><\/span>Sol em contato com o solo deixa o ar mais quente e consequentemente menos refringente <\/b><\/span><\/span><\/span>que o ar das <\/b><\/span><\/span><\/span>camadas<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

superiores.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Isso faz com que os raios de luz sofram reflex\u00e3o total <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>camadas pr\u00f3ximas ao solo e retornem subindo e atingindo os olhos de um observador, <\/b><\/span><\/span><\/span>que ter\u00e1 a <\/b><\/span><\/span><\/span>impress\u00e3o de que no solo existe um espelho fornecendo a imagem do objeto.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Observa\u00e7\u00e3o:<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>fen\u00f4meno <\/b><\/span><\/span><\/span>tamb\u00e9m <\/b><\/span><\/span><\/span>pode acontecer <\/b><\/span><\/span><\/span>embora menos frequentemente, <\/b><\/span><\/span><\/span>nos mares em regi\u00f5es frias, onde o<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span>ar \u201cfrio\u201d, mais denso e mais refringente, fica na camada inferior.<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00c0 medida que a<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>altura aumenta, o ar vai\u00a0ficando mais quente<\/b><\/span><\/span>, tornando-se<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>menos denso<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>e, portanto,<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>menos refringente, afastando-se da normal e sofrendo os sucessivos desvios (refra\u00e7\u00f5es) apresentados na figura que, est\u00e1 fora de escala.<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>
\nCada refra\u00e7\u00e3o<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>\u00e9 sempre acompanhada<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>de reflex\u00e3o que pode ou n\u00e3o ser reflex\u00e3o total.<\/b><\/span><\/span><\/span><\/span><\/p>\n

Assim, para um<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>observador, a imagem do iceberg, pode aparecer acima da \u00e1gua, como se estivesse flutuando no ar e, onde estava o iceberg ele pode apenas enxergar \u00e1gua.<\/b><\/span><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Brilho dos diamantes<\/b><\/span><\/span><\/span><\/p>\n

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

O <\/b><\/span><\/span><\/span>brilho intenso de um diamante \u00e9 devido \u00e0 reflex\u00e3o total. <\/b><\/span><\/span><\/span><\/p>\n

Seu \u00e2ngulo limite <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>muito pequeno<\/b><\/span><\/span><\/span>, da <\/b><\/span><\/span><\/span>ordem de 23<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> <\/b>e\u00a0<\/b><\/span><\/span><\/span>seu \u00edndice de refra\u00e7\u00e3o \u00e9 muito grande.<\/b><\/span><\/span><\/span><\/p>\n

Assim ele consegue \u201caprisionar\u201d a luz em seu interior <\/b><\/span><\/span><\/span>fazendo-a sofrer <\/b><\/span><\/span><\/span>in\u00fameras reflex\u00f5es totais e muito pouca refra\u00e7\u00e3o para o meio exterior.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"Al\u00e9m disso, ele \u00e9 <\/b><\/span><\/span><\/span>lapidado de maneira que a luz fique mais tempo dentro dele de modo que a luz incidente numa das faces seja totalmente refletida nas outras.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

Aquecedor solar<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>Sol emite v\u00e1rios tipos de radia\u00e7\u00f5es eletromagn\u00e9ticas <\/b><\/span><\/span><\/span>al\u00e9m da luz. <\/b><\/span><\/span><\/span><\/p>\n

Uma delas <\/b><\/span><\/span><\/span>\u00e9 a <\/b><\/span><\/span><\/span>radia\u00e7\u00e3o infravermelha, que transmite calor.<\/b><\/span><\/span><\/span><\/p>\n

Existe um tipo de <\/b><\/span><\/span><\/span>aquecedor solar que utiliza essa radia\u00e7\u00e3o para aquecer a \u00e1gua de uma casa.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0\u00c8 <\/b><\/span><\/span><\/span>constitu\u00eddo por um tubo em forma de serpentina que conduz a \u00e1gua e esse tubo<\/b><\/span><\/span><\/span>\u00a0\u00e9 <\/b><\/span><\/span><\/span>envolto <\/b><\/span><\/span><\/span>por um <\/b><\/span><\/span><\/span>isolante t\u00e9rmico e por duas placas de vidro <\/b><\/span><\/span><\/span>(principal e auxiliar) que <\/b><\/span><\/span><\/span>permitem a entrada da radia\u00e7\u00e3o infravermelha,\u00a0 mas a \u201caprisionam\u201d em seu interior atrav\u00e9s da reflex\u00e3o total.<\/b><\/span><\/span><\/span><\/p>\n

Essas radia\u00e7\u00f5es ficam refletindo no interior do vidro, aquecendo mais a \u00e1gua.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Se voc\u00ea tiver um <\/b><\/span><\/span><\/span>raio luminoso incidindo com \u00e2ngulo de 45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> sobre um cubo de vidro, <\/b><\/span><\/span><\/span>colocado <\/b><\/span><\/span><\/span>no ar (n<\/b><\/span><\/span><\/span>ar <\/b><\/span><\/span><\/sub><\/span>= 1), <\/b><\/span><\/span><\/span>como mostra a figura ao lado e quiser <\/b><\/span><\/span><\/span>calcular o \u00edndice de refra\u00e7\u00e3o n do vidro<\/b><\/span><\/span><\/span>, para que <\/b><\/span><\/span><\/span>haja internamente reflex\u00e3o total na face A<\/b><\/span><\/span><\/span>, voc\u00ea deve proceder da <\/b><\/span><\/span><\/span>seguinte maneira, considerando sen 45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>\u00a0=\u00a0\"\" \/2:<\/b><\/span><\/span><\/span><\/p>\n

Aplicar a lei de <\/b><\/span><\/span><\/span>Snell-Descartes <\/b><\/span><\/span><\/span>na <\/b><\/span><\/span><\/span>face superior<\/b><\/span><\/span><\/span> \"\" <\/b><\/span><\/span><\/span>n<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>.sen45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span> = n.senr\u00a0\"\" \u00a0<\/b><\/span><\/span><\/span>1.\u221a2\/2= n.senr\u00a0\u00a0\"\" \u00a0<\/b><\/span><\/span><\/span>senr = \u221a2\/2n\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Em seguida <\/b><\/span><\/span><\/span>completar a trajet\u00f3ria do raio de luz no interior do cubo at\u00e9 ele atingir o ponto P na face A (figura).<\/b><\/span><\/span><\/span><\/p>\n

Para que <\/b><\/span><\/span><\/span>haja reflex\u00e3o total no ponto P da face A, <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>\u00e2ngulo<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>incid\u00eancia i = (90<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>\u00a0\u2013 r) <\/b><\/span><\/span><\/span>deve ser <\/b><\/span><\/span><\/span>maior que o \u00e2ngulo limite L <\/b><\/span><\/span><\/span>ou seja, <\/b><\/span><\/span><\/span>sen (90<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sup><\/span>– r) > sem L\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0\u00a0impondo essa condi\u00e7\u00e3o \"\" sen (90<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/span>– r) >\u00a0sen L\u00a0\u00a0\"\"\u00a0 <\/b><\/span><\/span><\/span>cos r > senL\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 \u221a(1 \u2013 sen<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0r)\u00a0>\u00a0sen L\u00a0\"\"\u00a0 <\/b><\/span><\/span><\/span>(1 \u2013 sen<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0r)\u00a0>\u00a0sen<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0L\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0\u00a01 – 1\/2n<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0>\u00a01\/n<\/b><\/span><\/span><\/span>2\u00a0<\/b><\/span><\/span><\/sup><\/span>\u00a0\"\"\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span>2n<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0>\u00a03\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0\u00a0<\/b><\/span><\/span><\/span>n\u00a0>\u00a01,5.<\/b><\/span><\/span><\/span><\/p>\n

\"\" As <\/b><\/span><\/span><\/span>ondas eletromagn\u00e9ticas, <\/b><\/span><\/span><\/span>como a <\/b><\/span><\/span><\/span>luz vis\u00edvel e as ondas de r\u00e1dio,<\/b><\/span><\/span><\/span> viajam em <\/b><\/span><\/span><\/span>linha reta em um meio homog\u00eaneo.<\/b><\/span><\/span><\/span><\/p>\n

Ent\u00e3o, as <\/b><\/span><\/span><\/span>ondas de r\u00e1dio emitidas na regi\u00e3o litor\u00e2nea do Brasil n\u00e3o alcan\u00e7ariam <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>regi\u00e3o amaz\u00f4nica do Brasil <\/b><\/span><\/span><\/span>por causa da <\/b><\/span><\/span><\/span>curvatura da Terra. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

Entretanto sabemos que <\/b><\/span><\/span><\/span>\u00e9 poss\u00edvel transmitir ondas de r\u00e1dio <\/b><\/span><\/span><\/span>entre essas <\/b><\/span><\/span><\/span>localidades devido \u00e0 ionosfera.<\/b><\/span><\/span><\/span><\/p>\n

Com a <\/b><\/span><\/span><\/span>ajuda da ionosfera<\/b><\/span><\/span><\/span>, a <\/b><\/span><\/span><\/span>transmiss\u00e3o de ondas planas <\/b><\/span><\/span><\/span>entre o <\/b><\/span><\/span><\/span>litoral do Brasil e a regi\u00e3o amaz\u00f4nica \u00e9 poss\u00edvel\u00a0<\/b><\/span><\/span><\/span>por meio da <\/b><\/span><\/span><\/span>reflex\u00e3o total dessas ondas na ionosfera.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Quando um <\/b><\/span><\/span><\/span>feixe <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>luz monocrom\u00e1tico <\/b><\/span><\/span><\/span>vai da <\/b><\/span><\/span><\/span>\u00e1gua, de \u00edndice de refra\u00e7\u00e3o 1,3,<\/b><\/span><\/span><\/span> para <\/b><\/span><\/span><\/span>o ar, de<\/b><\/span><\/span><\/span><\/p>\n

\u00edndice de refra\u00e7\u00e3o 1,0, <\/b><\/span><\/span><\/span>pode <\/b><\/span><\/span><\/span>concluir que, para essa onda (luz)<\/b><\/span><\/span><\/span>, a <\/b><\/span><\/span><\/span>frequ\u00eancia n\u00e3o se altera <\/b><\/span><\/span><\/span>e o <\/b><\/span><\/span><\/span>comprimento de onda aumenta.\u00a0<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Isso ocorre porque a <\/b><\/span><\/span><\/span>frequ\u00eancia \u00e9 caracter\u00edstica de cada cor de luz<\/b><\/span><\/span><\/span>, e <\/b><\/span><\/span><\/span>\u00e9 a mesma para qualquer meio <\/b><\/span><\/span><\/span>desde que a <\/b><\/span><\/span><\/span>radia\u00e7\u00e3o (cor) seja a mesma.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Assim, ao <\/b><\/span><\/span><\/span>mudar de meio, a frequ\u00eancia do feixe n\u00e3o se altera, mas<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>comprimento de onda <\/b><\/span><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span> <\/b>pode ser <\/b><\/span><\/span><\/span>obtido a partir da lei de Snell\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>seni\/senr = n<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span>\/n<\/b><\/span><\/span><\/span>ar <\/b><\/span><\/span><\/sub><\/span>= V<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/sub><\/span>\/V<\/b><\/span><\/span><\/span>\u00e1gua <\/b><\/span><\/span><\/sub><\/span>= \u03bb<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/sub><\/span>\/ \u03bb<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span>\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 n<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span>\/n<\/b><\/span><\/span><\/span>ar <\/b><\/span><\/span><\/sub><\/span>= \u03bb<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/sub><\/span>\/ \u03bb<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span> \"\"\u00a0 se <\/b><\/span><\/span><\/span>n<\/b><\/span><\/span><\/span>\u00e1gua\u00a0<\/b><\/span><\/span><\/sub><\/span>> n<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/sub><\/span>\u00a0 \"\"\u00a0 \u03bb<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/sub><\/span>\u00a0> \u03bb<\/b><\/span><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub><\/span>\u00a0 (quanto menor o \u00edndice de refra\u00e7\u00e3o de um meio, maior ser\u00e1 o comprimento de onda da radia\u00e7\u00e3o no mesmo).<\/b><\/span><\/span><\/span><\/p>\n

\"\" Em virtude da <\/b><\/span><\/span><\/span>refra\u00e7\u00e3o na atmosfera terrestre,<\/b><\/span><\/span><\/span> um <\/b><\/span><\/span><\/span>observador na Terra <\/b><\/span><\/span><\/span>pode ver o Sol mesmo quando esse <\/b><\/span><\/span><\/span>est\u00e1 totalmente abaixo da linha do horizonte, como voc\u00ea pode observar na figura onde,<\/b><\/span><\/span><\/span><\/p>\n

\u00e0 medida que os <\/b><\/span><\/span><\/span>raios de luz provenientes do Sol penetram na atmosfera da Terra, <\/b><\/span><\/span><\/span>v\u00e3o<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

encontrando <\/b><\/span><\/span><\/span>camadas de ar cada vez mais densas, mais refringentes e de maiores \u00edndices de refra\u00e7\u00e3o<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>aproximam-se cada vez mais da normal <\/b><\/span><\/span><\/span>sofrendo os desvios mostrados.<\/b><\/span><\/span><\/span><\/p>\n

Esses <\/b><\/span><\/span><\/span>desvios fazem com que a imagem que se observa do Sol ao amanhecer <\/b><\/span><\/span><\/span>(antes de o Sol objeto aparecer) a e ao <\/b><\/span><\/span><\/span>anoitecer <\/b><\/span><\/span><\/span>(depois que o Sol objeto desapareceu)\u00a0<\/b><\/span><\/span><\/span>se encontre acima de sua real posi\u00e7\u00e3o, tomando-se como refer\u00eancia o horizonte.<\/b><\/span><\/span><\/span><\/p>\n

Ent\u00e3o, <\/b><\/span><\/span><\/span>como a <\/b><\/span><\/span><\/span>atmosfera \u00e9 transparente<\/b><\/span><\/span><\/span>, mas <\/b><\/span><\/span><\/span>n\u00e3o homog\u00eanea,<\/b><\/span><\/span><\/span> os <\/b><\/span><\/span><\/span>raios solares sofrem desvio <\/b><\/span><\/span><\/span>ao atravess\u00e1-la, fazendo com que o <\/b><\/span><\/span><\/span>p\u00f4r do sol seja uma miragem.<\/b><\/span><\/span><\/span><\/p>\n

Como, na <\/b><\/span><\/span><\/span>refra\u00e7\u00e3o, as radia\u00e7\u00f5es de menor frequ\u00eancia <\/b><\/span><\/span><\/span>(vermelha, amarela e alaranjada) <\/b><\/span><\/span><\/span>sofrem menor<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

desvio,<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>observador v\u00ea a imagem do Sol com predomin\u00e2ncia dessas cores<\/b><\/span><\/span><\/span>, da\u00ed, aquele <\/b><\/span><\/span><\/span>tom roseado<\/b><\/span><\/span><\/span> como ilustra a figura.<\/b><\/span><\/span><\/span><\/p>\n

Confira os exerc\u00edcios com resolu\u00e7\u00e3o comentada<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

Reflex\u00e3o Total Reflex\u00e3o total \u2013 \u00c2ngulo Limite (L) Considere um raio de luz se propagando de um meio menos refringente (ar,\u00a0nar = 1) para um meio mais refringente (\u00e1gua,\u00a0n\u00e1gua = 1,33), sendo i o \u00e2ngulo de incid\u00eancia e r o \u00e2ngulo de refra\u00e7\u00e3o. Nesse caso o raio refratado r se aproxima da normal. (Figura 1) Aumentando o \u00e2ngulo de incid\u00eancia<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2137,"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-2199","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2199","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=2199"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2199\/revisions"}],"predecessor-version":[{"id":2207,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2199\/revisions\/2207"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2137"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2199"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}