{"id":2139,"date":"2016-04-13T03:39:29","date_gmt":"2016-04-13T03:39:29","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2139"},"modified":"2024-09-02T14:25:18","modified_gmt":"2024-09-02T14:25:18","slug":"principios-da-propagacao-da-luz","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/optica\/optica-geometrica\/principios-da-propagacao-da-luz\/","title":{"rendered":"Princ\u00edpios da Propaga\u00e7\u00e3o da Luz"},"content":{"rendered":"

Princ\u00edpios da Propaga\u00e7\u00e3o da Luz<\/b><\/span><\/span><\/span><\/p>\n

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

Conceitos e defini\u00e7\u00f5es sobre luz<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0 <\/span>Conceito de Luz<\/b><\/span><\/span><\/span> \"\"<\/b><\/span><\/span><\/span> <\/b>Grandeza f\u00edsica <\/b><\/span><\/span><\/span>(forma de <\/b><\/span><\/span><\/span>energia radiante<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>que \u00e9 um tipo de energia que se <\/b><\/span><\/span><\/span>propaga por meio de ondas eletromagn\u00e9ticas, <\/b><\/span><\/span><\/span>como: ondas de r\u00e1dio, TV, micro-ondas, <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

raios x, raios infra vermelho, radia\u00e7\u00f5es ultra violeta, etc., e inclusive a <\/b><\/span><\/span><\/span>luz\u00a0<\/b><\/span><\/span><\/span>) <\/b><\/span><\/span><\/span>emitida<\/b><\/span><\/span><\/span> por certas <\/b><\/span><\/span><\/span>subst\u00e2ncias <\/b><\/span><\/span><\/span>e sob certas circunst\u00e2ncias, que nos <\/b><\/span><\/span><\/span>permite enxergar <\/b><\/span><\/span><\/span>(<\/b><\/span><\/span><\/span>atuando nos <\/span><\/span><\/span>\u00f3rg\u00e3os visuais, <\/span><\/span><\/span>produz a <\/span><\/span><\/span>sensa\u00e7\u00e3o da vis\u00e3o<\/span><\/span><\/span>)<\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>fotografar, filmar, etc.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

\"\"<\/p>\n

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

\"\"<\/p>\n

\"\"<\/p>\n

Defini\u00e7\u00e3o de ano-luz<\/b><\/span><\/span><\/span><\/p>\n

Como as <\/b><\/span><\/span><\/span>dist\u00e2ncias percorridas pela luz, das estrelas, dos planetas, do Sol, at\u00e9 a Terra possuem ordens de grandezas muito elevadas, <\/b><\/span><\/span><\/span>costuma-se <\/b><\/span><\/span><\/span>medi-las em\u00a0<\/b><\/span><\/span><\/span>ano-luz<\/b><\/span><\/span><\/span>, que \u00e9 <\/b><\/span><\/span><\/span>definido como sendo <\/b><\/span><\/span><\/span>a\u00a0<\/b><\/span><\/span><\/span>dist\u00e2ncia <\/b><\/span><\/span><\/span>percorrida pela luz, no <\/b><\/span><\/span><\/span>v\u00e1cuo<\/b><\/span><\/span><\/span>, em um ano com velocidade v = 3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>m\/s.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Esse <\/b><\/span><\/span><\/span>valor equivale <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>V = \u0394S\/\u0394t\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0 <\/span>V = 3,0.10<\/b><\/span><\/span><\/span>8 <\/b><\/span><\/span><\/sup><\/span>m\/s\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>\u0394t = 1 ano <\/b><\/span><\/span><\/span>em segundos\u00a0=\u00a03,1.10<\/b><\/span><\/span><\/span>7<\/b><\/span><\/span><\/sup><\/span>s\u00a0 \"\" 3,0.10<\/b><\/span><\/span><\/span>8 <\/b><\/span><\/span><\/sup><\/span> = \u0394S\/3,1.10<\/b><\/span><\/span><\/span>7<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\" <\/b><\/span><\/span><\/span>\u0394S \u22489,5.10<\/b><\/span><\/span><\/span>15<\/b><\/span><\/span><\/sup><\/span>m\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>essa\u00a0<\/b><\/span><\/span><\/span>dist\u00e2ncia<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>corresponde a <\/b><\/span><\/span><\/span>1 ano luz.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Raios de luz ou raios luminosos<\/b><\/span><\/span><\/span><\/p>\n

\u00a0A <\/b><\/span><\/span><\/span>propaga\u00e7\u00e3o da luz \u00e9 representada pelos raios de luz (raios luminosos) que s\u00e3o linhas orientadas que indicam a dire\u00e7\u00e3o e o sentido de propaga\u00e7\u00e3o da luz que \u00e9 indicado por uma seta.<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

Fisicamente, os <\/b><\/span><\/span><\/span>raios de luz n\u00e3o existem <\/b><\/span><\/span><\/span>sendo apenas <\/b><\/span><\/span><\/span>elementos geom\u00e9tricos que facilitam nosso estudo da \u00f3ptica geom\u00e9trica.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Feixe ou pincel de luz<\/b><\/span><\/span><\/span><\/p>\n

Trata-se de um conjunto de raios de luz<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Fonte de luz<\/b><\/span><\/span><\/span><\/p>\n

Uma <\/b><\/span><\/span><\/span>fonte de luz ou uma fonte luminosa <\/b><\/span><\/span><\/span>pode ser <\/b><\/span><\/span><\/span>qualquer corpo vis\u00edvel <\/b><\/span><\/span><\/span>ou <\/b><\/span><\/span><\/span>qualquer corpo capaz de emitir luz.<\/b><\/span><\/span><\/span><\/p>\n

Pode ser:<\/b><\/span><\/span><\/span><\/p>\n

\"\" Prim\u00e1ria (corpo luminoso<\/b><\/span><\/span><\/span>) <\/b><\/span><\/span><\/span> \"\" <\/b><\/span><\/span><\/span>emite luz pr\u00f3pria \"\" <\/b><\/span><\/span><\/span>exemplos, <\/b><\/span><\/span><\/span>Sol, l\u00e2mpada acesa, chama<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

de uma vela, estrelas, etc.<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0\u00a0<\/span>Secund\u00e1ria (corpo iluminado) \"\"<\/b><\/span><\/span><\/span>\u00a0 recebe a luz de uma fonte prim\u00e1ria e a reflete (difunde)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\" exemplo, <\/b><\/span><\/span><\/span>Lua, mesa, parede, etc.<\/b><\/span><\/span><\/span><\/p>\n

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

Princ\u00edpios da propaga\u00e7\u00e3o da luz<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Princ\u00edpio da propaga\u00e7\u00e3o retil\u00ednea da luz<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>princ\u00edpio da propaga\u00e7\u00e3o retil\u00ednea da luz pode ser definido<\/b><\/span><\/span><\/span> como: <\/b><\/span><\/span><\/span>\u201cem meios homog\u00eaneos e transparentes a luz se propaga em linha reta\u201d<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Este <\/b><\/span><\/span><\/span>princ\u00edpio pode ser comprovado pelas figuras acima onde objetos e suas respectivas sombras<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

possuem semelhan\u00e7as geom\u00e9tricas <\/b><\/span><\/span><\/span>ou pelas figuras acima onde o observador <\/b><\/span><\/span><\/span>s\u00f3 enxergar\u00e1 a chama da vela se os orif\u00edcios estiverem em linha reta <\/b><\/span><\/span><\/span>e onde o <\/b><\/span><\/span><\/span>laser emite luz se propagando em linha reta<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Princ\u00edpio da Independ\u00eancia dos raios luminosos<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>princ\u00edpio da independ\u00eancia dos raios luminosos <\/b><\/span><\/span><\/span>afirma que: <\/b><\/span><\/span><\/span>\u201c feixes de luz podem se cruzar se que um altere a propaga\u00e7\u00e3o do outro\u201d<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Observe na <\/b><\/span><\/span><\/span>figura acima que,<\/b><\/span><\/span><\/span> <\/b>ap\u00f3s se cruzarem os raios de luz continuam seus caminhos como se nada tivesse acontecido.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

Princ\u00edpio da reversibilidade dos raios luminosos<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>princ\u00edpio da reversibilidade dos raios luminosos <\/b><\/span><\/span><\/span>afirma que: <\/b><\/span><\/span><\/span>\u201cA trajet\u00f3ria de um raio de luz permanece a mesma quando se inverte o seu sentido de propaga\u00e7\u00e3o\u201d<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Devido \u00e0 <\/b><\/span><\/span><\/span>esse princ\u00edpio, na figura da esquerda acima<\/b><\/span><\/span><\/span>, se os <\/b><\/span><\/span><\/span>olhos do motorista est\u00e3o enxergando os olhos do passageiro, os olhos do passageiro tamb\u00e9m enxergar\u00e3o os olhos do motorista <\/b><\/span><\/span><\/span>e na <\/b><\/span><\/span><\/span>figura da direita <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>trajet\u00f3ria dos raios de luz \u00e9 a mesma, independente de as fontes estarem em P ou em Q.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

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

Se voc\u00ea <\/b><\/span><\/span><\/span>est\u00e1 enxergando um objeto, certamente os infinitos raios de luz emitidos pelo objeto devem atingir seus olhos.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Os <\/b><\/span><\/span><\/span>raios de luz\u00a0<\/b><\/span><\/span><\/span>est\u00e3o sempre dirigidos do objeto para o olho<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Meios \u00f3pticos<\/b><\/span><\/span><\/span><\/p>\n

Para se <\/b><\/span><\/span><\/span>enxergar um corpo <\/b><\/span><\/span><\/span>(no nosso exemplo, a borboleta), a <\/b><\/span><\/span><\/span>luz emitida por ela deve atravessar o meio e atingir os olhos do observador.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Como o <\/b><\/span><\/span><\/span>meio transparente <\/b><\/span><\/span><\/span>(figura I) <\/b><\/span><\/span><\/span>permite a vis\u00e3o n\u00edtida do objeto, <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>seu interior, os raios de luz percorrem trajet\u00f3rias regulares, at\u00e9 chegarem ao olho do observador.<\/b><\/span><\/span><\/span><\/p>\n

No <\/b><\/span><\/span><\/span>meio transl\u00facido <\/b><\/span><\/span><\/span>(figura II<\/b><\/span><\/span><\/span>), a vis\u00e3o do objeto n\u00e3o \u00e9 n\u00edtida <\/b><\/span><\/span><\/span>e, em <\/b><\/span><\/span><\/span>seu interior os raios de luz percorrem trajet\u00f3rias irregulares, at\u00e9 chegarem ao olho do observador. <\/b><\/span><\/span><\/span><\/p>\n

Nos meios opacos <\/b><\/span><\/span><\/span>(figura III) <\/b><\/span><\/span><\/span>a luz n\u00e3o se propaga e o observador n\u00e3o enxerga o objeto.<\/b><\/span><\/span><\/span><\/p>\n

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

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

\"\"\u00a0<\/span>Conhecer e entender os tr\u00eas princ\u00edpios de propaga\u00e7\u00e3o da luz.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0Lembrar que <\/b><\/span><\/span><\/span>ano luz \u00e9 medida de\u00a0<\/b><\/span><\/span><\/span>dist\u00e2ncia<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>(<\/b><\/span><\/span><\/span>dist\u00e2ncia <\/b><\/span><\/span><\/span>que a luz percorre em <\/b><\/span><\/span><\/span>um ano, no v\u00e1cuo <\/b><\/span><\/span><\/span>e aproximadamente no ar, com <\/b><\/span><\/span><\/span>velocidade de 3,0.10<\/b><\/span><\/span><\/span>8 <\/b><\/span><\/span><\/sup><\/span>m\/s.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Consequ\u00eancias da propaga\u00e7\u00e3o retil\u00ednea da luz<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

\"\" Fonte extensa<\/b><\/span><\/span><\/span>\u00a0(tamanho n\u00e3o desprez\u00edvel) \"\" projeta sombra e penumbra.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

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

\"\"<\/p>\n

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

Analise com aten\u00e7\u00e3o todos os detalhes da figura abaixo:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

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

\"\"<\/p>\n

Eclipse lunar<\/b><\/span><\/span><\/span><\/p>\n

Analise com aten\u00e7\u00e3o todos os detalhes da figura abaixo:<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

Fases da Lua<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>eclipse solar <\/b><\/span><\/span><\/span>ocorre quando a Lua est\u00e1 <\/b><\/span><\/span><\/span>na fase Nova e um eclipse da Lua quando est\u00e1 na fase cheia (veja figura).<\/b><\/span><\/span><\/span><\/p>\n

Per\u00edodo de luna\u00e7\u00e3o <\/b><\/span><\/span><\/span>corresponde ao <\/b><\/span><\/span><\/span>intervalo de tempo compreendido entre duas Luas novas consecutivas que \u00e9 de aproximadamente 30 dias (29 dias, 12 horas e 44 minutos). <\/b><\/span><\/span><\/span><\/p>\n

Como o <\/b><\/span><\/span><\/span>eclipse solar ocorre na Lua nova e o lunar na Lua cheia, <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>intervalo de tempo m\u00ednimo <\/b><\/span><\/span><\/span>entre um <\/b><\/span><\/span><\/span>eclipse solar e um lunar deve ser da metade desse valor (aproximadamente 15 dias, duas semanas), que \u00e9 o tempo que a Lua para passar da fase de Lua nova para a fase de Lua cheia.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

C\u00e2mara escura de orif\u00edcio<\/b><\/span><\/span><\/span><\/p>\n

Trata-se do <\/b><\/span><\/span><\/span>princ\u00edpio de funcionamento de uma m\u00e1quina fotogr\u00e1fica <\/b><\/span><\/span><\/span>baseado na <\/b><\/span><\/span><\/span>propaga\u00e7\u00e3o retil\u00ednea da luz.<\/b><\/span><\/span><\/span><\/p>\n

Todos os <\/b><\/span><\/span><\/span>infinitos raios de luz que s\u00e3o emitidos pelo objeto <\/b><\/span><\/span><\/span>a ser projetado, <\/b><\/span><\/span><\/span>passam atrav\u00e9s de um pequeno orif\u00edcio e atingem a parte interior oposta da c\u00e2mara. .<\/b><\/span><\/span><\/span><\/p>\n

Com isso a <\/b><\/span><\/span><\/span>luz que sai do ponto (A) superior do objeto (no nosso exemplo, borboleta) <\/b><\/span><\/span><\/span>atingir\u00e1 a <\/b><\/span><\/span><\/span>parede oposta no ponto inferior (A\u2019) da imagem projetada<\/b><\/span><\/span><\/span>, formando uma <\/b><\/span><\/span><\/span>imagem invertida<\/b><\/span><\/span><\/span>, conforme a figura.<\/b><\/span><\/span><\/span><\/p>\n

O mesmo acontece <\/b><\/span><\/span><\/span>nas partes laterais<\/b><\/span><\/span><\/span>, trocando a <\/b><\/span><\/span><\/span>direita pela esquerda (imagem reversa).<\/b><\/span><\/span><\/span><\/p>\n

\"\"
\n<\/b><\/span><\/span><\/span>Semelhan\u00e7a de tri\u00e2ngulos\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span> \"\" =\"\"<\/b><\/span><\/span><\/span>\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 observe que <\/b><\/span><\/span><\/span>objeto e imagem trocam cima por baixo (invertida) e direita pela esquerda (reversa).\u00a0 \u00a0<\/b><\/span><\/span><\/span><\/p>\n

Se o <\/b><\/span><\/span><\/span>orif\u00edcio da c\u00e2mara for aumentado a nitidez da imagem diminui e sua luminosidade aumenta.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Compara\u00e7\u00e3o entre o globo ocular e uma m\u00e1quina fotogr\u00e1fica<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

C\u00e1lculo da altura de um edif\u00edcio<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

N\u00e3o \u00e9 poss\u00edvel visualizar um pincel de luz.<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>m\u00e1ximo que conseguimos \u00e9 visualizar sua forma <\/b><\/span><\/span><\/span>se <\/b><\/span><\/span><\/span>jogarmos farinha, talco, fuma\u00e7a,<\/b><\/span><\/span><\/span> neblina, nuvens, poeira, spray de inseticida ou perfume no ar, etc<\/b><\/span><\/span><\/span>.<\/span><\/span><\/span>\u00a0<\/span><\/span><\/span>ou <\/b><\/span><\/span><\/span>outro algum outro tipo de material particulado (part\u00edculas coloidais) sobre ele.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Neste caso <\/b><\/span><\/span><\/span>poderemos observar as part\u00edculas do talco, da farinha, da fuma\u00e7a, da neblina mas n\u00e3o o pincel de luz. <\/b><\/span><\/span><\/span><\/p>\n

Este fen\u00f4meno, tamb\u00e9m observado quando <\/b><\/span><\/span><\/span>voc\u00ea abre a janela do seu quarto de manh\u00e3, deixando a luz do Sol entrar, \u00e9 conhecido como efeito Tyndall.<\/b><\/span><\/span><\/span><\/p>\n

Efeito Tyndall <\/b><\/span><\/span><\/span>corresponde a um <\/b><\/span><\/span><\/span>efeito \u00f3ptico provocado pela dispers\u00e3o (espalhamento) da luz nas part\u00edculas coloidais, oferecendo um aspecto nebuloso, opaco, turvo.<\/b><\/span><\/span><\/span><\/p>\n

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

Cor de um corpo<\/span><\/span><\/span><\/p>\n

\u00a0A <\/b><\/span><\/span><\/span>luz branca do Sol ou de uma l\u00e2mpada <\/b><\/span><\/span><\/span>qualquer \u00e9 denominada <\/b><\/span><\/span><\/span>luz policrom\u00e1tica (v\u00e1rias cores) <\/b><\/span><\/span><\/span>e \u00e9 composta das <\/b><\/span><\/span><\/span>cores monocrom\u00e1ticas (uma s\u00f3 cor), vermelho, alaranjado, amarelo, verde, azul, anil e violeta.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>cor apresentada por um corpo, <\/b><\/span><\/span><\/span>ao ser iluminado, <\/b><\/span><\/span><\/span>depende do tipo de luz que ele reflete difusamente<\/b><\/span><\/span><\/span> (espalha em todas as dire\u00e7\u00f5es e sentidos) e <\/b><\/span><\/span><\/span>que chega aos olhos do observador.<\/b><\/span><\/span><\/span><\/p>\n

Um <\/b><\/span><\/span><\/span>corpo negro absorve todas as cores<\/b><\/span><\/span><\/span> <\/b>e um <\/b><\/span><\/span><\/span>corpo branco reflete todas as cores.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0Figura 1 \"\"<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>corpo vermelho <\/b><\/span><\/span><\/span>reflete difusamente <\/b><\/span><\/span><\/span>apenas a cor vermelha <\/b><\/span><\/span><\/span>e o <\/b><\/span><\/span><\/span>observador enxergar\u00e1 vermelho.<\/b><\/span><\/span><\/span><\/p>\n

Figura 2 \"\"<\/b><\/span><\/span><\/span> As <\/b><\/span><\/span><\/span>sete cores (policrom\u00e1tica branca)<\/b><\/span><\/span><\/span> <\/b>incidem<\/b><\/span><\/span><\/span> sobre o <\/b><\/span><\/span><\/span>corpo amarelo que reflete difusamente somente o amarelo<\/b><\/span><\/span><\/span> e o <\/b><\/span><\/span><\/span>observador enxergar\u00e1 essa cor.<\/b><\/span><\/span><\/span><\/p>\n

Figura 3 \"\"<\/b><\/span><\/span><\/span>\u00a0 As <\/b><\/span><\/span><\/span>sete cores (policrom\u00e1tica branca) incidem<\/b><\/span><\/span><\/span> sobre o <\/b><\/span><\/span><\/span>corpo verde que reflete difusamente somente o verde <\/b><\/span><\/span><\/span>e o observador <\/b><\/span><\/span><\/span>enxergar\u00e1 verde.<\/b><\/span><\/span><\/span><\/p>\n

Figura 4 \"\" <\/b><\/span><\/span><\/span> <\/b>O corpo negro absorve todas as cores<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>nenhuma chegar\u00e1 ao observador <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>ver\u00e1 negro (aus\u00eancia de cores).<\/b><\/span><\/span><\/span><\/p>\n

Figura 5 \"\"<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>corpo violeta reflete difusamente somente o violeta <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>absorver\u00e1 o verde, <\/b><\/span><\/span><\/span>n\u00e3o <\/b><\/span><\/span><\/span>chegando nenhuma luz ao observador, que ver\u00e1 negro.<\/b><\/span><\/span><\/span><\/p>\n

Figura 6 \"\"<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>observador ver\u00e1 vermelho<\/b><\/span><\/span><\/span>, pois o <\/b><\/span><\/span><\/span>corpo branco reflete difusamente todas as cores inclusive o vermelho.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Apesar da <\/b><\/span><\/span><\/span>luz branca ser formada por todas as cores,<\/b><\/span><\/span><\/span> para se ter a <\/b><\/span><\/span><\/span>sensa\u00e7\u00e3o de luz branca <\/b><\/span><\/span><\/span>n\u00e3o \u00e9 preciso todas as cores juntas, mas <\/b><\/span><\/span><\/span>apenas tr\u00eas cores, as chamadas cores prim\u00e1rias<\/b><\/span><\/span><\/span><\/p>\n

\u00a0As <\/b><\/span><\/span><\/span>cores prim\u00e1rias s\u00e3o as cores mais puras de todas<\/b><\/span><\/span><\/span> e, com <\/b><\/span><\/span><\/span>sua mistura pode-se produzir qualquer cor. <\/b><\/span><\/span><\/span><\/p>\n

As cores\u00a0<\/b><\/span><\/span><\/span>prim\u00e1rias<\/b><\/span><\/span><\/span>\u00a0s\u00e3o o amarelo, o vermelho e o azul.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

As <\/b><\/span><\/span><\/span>cores\u00a0<\/b><\/span><\/span><\/span>secund\u00e1ria<\/b><\/span><\/span><\/span>s <\/b><\/span><\/span><\/span>s\u00e3o formadas <\/b><\/span><\/span><\/span>pela mistura das cores prim\u00e1ria e s\u00e3o,\u00a0<\/b><\/span><\/span><\/span>o verde, o roxo e o<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>orif\u00edcio de uma c\u00e2mara escura <\/b><\/span><\/span><\/span>est\u00e1 <\/b><\/span><\/span><\/span>voltada para o c\u00e9u, numa noite estrelada<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>parede oposta ao orif\u00edcio \u00e9 feita de papel vegetal transl\u00facido. <\/b><\/span><\/span><\/span>\"\"<\/p>\n

Um <\/b><\/span><\/span><\/span>observador que est\u00e1 atr\u00e1s da c\u00e2mara, <\/b><\/span><\/span><\/span>se <\/b><\/span><\/span><\/span>olhasse diretamente para o c\u00e9u, veria o Cruzeiro do Sul conforme <\/b><\/span><\/span><\/span>a figura 1. <\/b><\/span><\/span><\/span><\/p>\n

Olhando a imagem<\/b><\/span><\/span><\/span>, no <\/b><\/span><\/span><\/span>papel vegetal, por tr\u00e1s da c\u00e2mara<\/b><\/span><\/span><\/span>, o observador <\/b><\/span><\/span><\/span>v\u00ea o Cruzeiro do Sul conforme a <\/b><\/span><\/span><\/span>figura 2, <\/b><\/span><\/span><\/span>onde a <\/b><\/span><\/span><\/span>imagem formada <\/b><\/span><\/span><\/span>fica invertida duas vezes, uma <\/b><\/span><\/span><\/span>horizontal<\/b><\/span><\/span><\/span>, trocando direita por esquerda e outra <\/b><\/span><\/span><\/span>vertical,<\/b><\/span><\/span><\/span> trocando cima por baixo.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Analise esse exerc\u00edcio:<\/b><\/span><\/span><\/span> <\/b>No <\/b><\/span><\/span><\/span>instante t=0, um feixe horizontal de raios luminosos<\/b><\/span><\/span><\/span>, provenientes da <\/b><\/span><\/span><\/span>\"\"<\/p>\n

chama de uma <\/b><\/span><\/span><\/span>vela A, atravessa um pequeno orif\u00edcio de um fino anteparo e projeta uma pequena mancha luminosa B no anteparo vertical, conforme figura.<\/b><\/span><\/span><\/span><\/p>\n

As <\/b><\/span><\/span><\/span>dist\u00e2ncias da chama ao orif\u00edcio e do orif\u00edcio ao anteparo s\u00e3o, respectivamente, a e 2a.<\/b><\/span><\/span><\/span><\/p>\n

Se a vela <\/b><\/span><\/span><\/span>queima a uma velocidade V\u2019 = 2,0cm\/min, ent\u00e3o a mancha luminosa se desloca verticalmente para cima sobre o anteparo com velocidade de quantos cm\/min? <\/b><\/span><\/span><\/span><\/p>\n

Resolu\u00e7\u00e3o: <\/b><\/span><\/span><\/span>Se a <\/b><\/span><\/span><\/span>vela queima a uma velocidade de V\u2019 = 2cm\/min, <\/b><\/span><\/span><\/span>ap\u00f3s um <\/b><\/span><\/span><\/span>minuto ele desceu d = 2cm <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>sua proje\u00e7\u00e3o na parede subiu at\u00e9 o ponto C de uma dist\u00e2ncia x.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Semelhan\u00e7a de tri\u00e2ngulos\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>a\/2 = 2.a \/x \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>x = 4cm\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 em <\/b><\/span><\/span><\/span>\u0394t = 1min \"\"<\/b><\/span><\/span><\/span> \u0394S = <\/b><\/span><\/span><\/span>x = 4 cm \"\"<\/b><\/span><\/span><\/span><\/p>\n

V\u2019\u2019 = \u0394S\/ \u0394t\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>V\u2019\u2019 <\/b><\/span><\/span><\/span>= 4\/1 <\/b><\/span><\/span><\/span>= 4cm\/min.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

Analise esse exerc\u00edcio:<\/b><\/span><\/span><\/span> O <\/b><\/span><\/span><\/span>por\u00e3o de uma antiga casa possui uma estreita clarab\u00f3ia quadrada <\/b><\/span><\/span><\/span>de 100 cm<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sup><\/span>de \u00e1rea, que <\/b><\/span><\/span><\/span>permite a entrada da luz do exterior<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>refletida difusamente <\/b><\/span><\/span><\/span>pelas constru\u00e7\u00f5es que a cercam. Na <\/b><\/span><\/span><\/span>ilustra\u00e7\u00e3o, vemos uma aranha, um rato <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>um gato, <\/b><\/span><\/span><\/span>que se <\/b><\/span><\/span><\/span>encontram parados no mesmo plano vertical que intercepta o centro da geladeira e o centro da clarab\u00f3ia. <\/b><\/span><\/span><\/span>Sendo a <\/b><\/span><\/span><\/span>clarab\u00f3ia a fonte luminosa,<\/b><\/span><\/span><\/span> pode-se dizer que, devido \u00e0 <\/b><\/span><\/span><\/span>interposi\u00e7\u00e3o da geladeira, a aranha, o rato e o gato, nesta ordem, est\u00e3o em regi\u00f5es de:<\/b><\/span><\/span><\/span>\"\"<\/p>\n

a) <\/b><\/span><\/span><\/span>luz, luz e penumbra.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>penumbra, luz e penumbra.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

c) <\/b><\/span><\/span><\/span>sombra, penumbra e luz.\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

d) <\/b><\/span><\/span><\/span>luz, penumbra e sombra.\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

e) <\/b><\/span><\/span><\/span>penumbra, sombra e sombra<\/b><\/span><\/span><\/span><\/p>\n

Resolu\u00e7\u00e3o: <\/b><\/span><\/span><\/span>A <\/b><\/span><\/span><\/span>clarab\u00f3ia se comporta como uma fonte extensa de luz<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>delimitada<\/b><\/span><\/span><\/span> pela <\/b><\/span><\/span><\/span>parte superior esquerda da geladeira, e as regi\u00f5es de iluminada, de sombra e penumbra, <\/b><\/span><\/span><\/span>est\u00e3o indicadas na<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

figura<\/b><\/span><\/span><\/span> onde voc\u00ea deve <\/b><\/span><\/span><\/span>observar com aten\u00e7\u00e3o a sequ\u00eancia indicada <\/b><\/span><\/span><\/span>e, ap\u00f3s a <\/b><\/span><\/span><\/span>superposi\u00e7\u00e3o das duas figuras da esquerda, <\/b><\/span><\/span><\/span>localizar na <\/b><\/span><\/span><\/span>figura da direita as regi\u00f5es onde est\u00e3o cada elemento:<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>aranha<\/b><\/span><\/span><\/span> est\u00e1 na <\/b><\/span><\/span><\/span>regi\u00e3o iluminada <\/b><\/span><\/span><\/span>pois <\/b><\/span><\/span><\/span>recebe toda a luz proveniente da claraboia.<\/b><\/span><\/span><\/span><\/p>\n

O rato <\/b><\/span><\/span><\/span>recebe <\/b><\/span><\/span><\/span>apenas parte da luz proveniente da claraboia, portanto est\u00e1 na regi\u00e3o de penumbra.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

O gato <\/b><\/span><\/span><\/span>est\u00e1 na <\/b><\/span><\/span><\/span>regi\u00e3o de sombra e n\u00e3o recebe luz nenhuma da claraboia.<\/b><\/span><\/span><\/span><\/p>\n

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

 <\/p>\n

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

Princ\u00edpios da Propaga\u00e7\u00e3o da Luz \u00a0 Conceitos e defini\u00e7\u00f5es sobre luz \u00a0 Conceito de Luz Grandeza f\u00edsica (forma de energia radiante, que \u00e9 um tipo de energia que se propaga por meio de ondas eletromagn\u00e9ticas, como: ondas de r\u00e1dio, TV, micro-ondas, raios x, raios infra vermelho, radia\u00e7\u00f5es ultra violeta, etc., e inclusive a luz\u00a0) emitida por certas subst\u00e2ncias e sob<\/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-2139","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2139","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=2139"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2139\/revisions"}],"predecessor-version":[{"id":2147,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2139\/revisions\/2147"}],"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=2139"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}