{"id":2478,"date":"2016-09-18T22:14:57","date_gmt":"2016-09-18T22:14:57","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2478"},"modified":"2024-08-21T13:30:54","modified_gmt":"2024-08-21T13:30:54","slug":"efeito-fotoeletrico-2","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/fisica-moderna\/efeito-fotoeletrico-2\/","title":{"rendered":"Efeito Fotoel\u00e9trico"},"content":{"rendered":"

Efeito Fotoel\u00e9trico<\/b><\/span><\/span><\/span><\/p>\n

Introdu\u00e7\u00e3o \u00e0 F\u00edsica Moderna<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>F\u00edsica cl\u00e1ssica, <\/b><\/span><\/span><\/span>das <\/b><\/span><\/span><\/span>leis <\/b><\/span><\/span><\/span>que regem os a <\/b><\/span><\/span><\/span>Cinem\u00e1tica, a Din\u00e2mica, a \u00d3ptica, a Ondulat\u00f3ria, o Eletromagnetismo, etc. <\/b><\/span><\/span><\/span>que <\/b><\/span><\/span><\/span>explicam<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>funcionamento dos nossos aparelhos el\u00e9tricos<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>eletr\u00f4nicos, dos carros, trens, \u00a0e que s\u00e3o partes importantes e relevantes da F\u00edsica, <\/b><\/span><\/span><\/span>continua <\/b><\/span><\/span><\/span>sendo v\u00e1lida, precisa, \u00a0e at\u00e9 sendo aperfei\u00e7oada.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

No entanto, <\/b><\/span><\/span><\/span>s\u00f3 \u00e9 aplic\u00e1vel dentro de determinados limites.<\/b><\/span><\/span><\/span><\/p>\n

Mas, quando voc\u00ea quer <\/b><\/span><\/span><\/span>resolver problemas que envolvam ordens de grandeza na \u00a0descri\u00e7\u00e3o da natureza, de ordens muito pequenas (micro) at\u00e9 ordens muito elevadas (macro) deve-se recorrer \u00e0 f\u00edsica moderna cuja evolu\u00e7\u00e3o<\/b><\/span><\/span><\/span>, a partir do s\u00e9culo XIX e in\u00edcio de\u00a0 XX se tornou <\/b><\/span><\/span><\/span>vertiginosa, teoricamente e tecnologicamente.<\/b><\/span><\/span><\/span><\/p>\n

Gra\u00e7as <\/b><\/span><\/span><\/span>F\u00edsica Moderna surgiram in\u00fameras descobertas cient\u00edficas <\/b><\/span><\/span><\/span>em <\/b><\/span><\/span><\/span>todos os ramos da f\u00edsica, <\/b><\/span><\/span><\/span>desde a <\/b><\/span><\/span><\/span>medicina at\u00e9 a f\u00edsica at\u00f4mica e nuclear, que est\u00e3o sendo utilizadas no benef\u00edcio da humanidade.<\/b><\/span><\/span><\/span><\/p>\n

Algumas, <\/b><\/span><\/span><\/span>dentre<\/b><\/span><\/span><\/span> as <\/b><\/span><\/span><\/span>in\u00fameras:<\/b><\/span><\/span><\/span> <\/b>Telefones celulares, micro computadores, c\u00e2meras digitais,<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"transmiss\u00e3o <\/b><\/span><\/span><\/span>de<\/b><\/span><\/span><\/span> sons e imagens <\/b><\/span><\/span><\/span>em<\/b><\/span><\/span><\/span> tempo real <\/b><\/span><\/span><\/span>atrav\u00e9s de <\/b><\/span><\/span><\/span>sat\u00e9lites artificiais, c\u00e9lulas fotoel\u00e9tricas, raios X, ultra-sons, resson\u00e2ncia magn\u00e9tica, cirurgias a laser, inje\u00e7\u00e3o eletr\u00f4nica <\/b><\/span><\/span><\/span>nos carros, etc.<\/b><\/span><\/span><\/span><\/p>\n

Devido ao fato de a <\/b><\/span><\/span><\/span>F\u00edsica Moderna estar muito relacionada com o funcionamento <\/b><\/span><\/span><\/span>de <\/b><\/span><\/span><\/span>muitos aparelhos do cotidiano da maioria das pessoas, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>introdu\u00e7\u00e3o<\/b><\/span><\/span><\/span> do assunto no <\/b><\/span><\/span><\/span>ensino m\u00e9dio \u00e9 muito interessante, <\/b><\/span><\/span><\/span>e seu <\/b><\/span><\/span><\/span>conte\u00fado est\u00e1 sendo exigido cada vez mais nos principais vestibulares do pa\u00eds.<\/b><\/span><\/span><\/span><\/p>\n

Resumo hist\u00f3rico da F\u00edsica Moderna<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>F\u00edsica Moderna <\/b><\/span><\/span><\/span>come\u00e7ou a ser <\/b><\/span><\/span><\/span>pesquisada e desenvolvida no final do s\u00e9culo XIX <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>in\u00edcio do s\u00e9culo XX,<\/b><\/span><\/span><\/span> principalmente nas <\/b><\/span><\/span><\/span>tr\u00eas primeiras d\u00e9cadas do s\u00e9culo passado e <\/b><\/span><\/span><\/span>principalmente <\/b><\/span><\/span><\/span>atrav\u00e9s da teoria da relatividade proposta por Albert Einstein e a teoria<\/b><\/span><\/span><\/span>\"\"<\/p>\n

qu\u00e2ntica proposta por Max Planck. <\/b><\/span><\/span><\/span><\/p>\n

Toda <\/b><\/span><\/span><\/span>essa teoria j\u00e1 resultou, no final do s\u00e9culo XX, em toda tecnologia conhecida hoje.<\/b><\/span><\/span><\/span><\/p>\n

Atualmente<\/b><\/span><\/span><\/span> a tentativa \u00e9 <\/b><\/span><\/span><\/span>unificar a teoria da relatividade\u00a0 com a teoria da mec\u00e2nica qu\u00e2ntica <\/b><\/span><\/span><\/span>na tend\u00eancia de <\/b><\/span><\/span><\/span>explicar o Universo, do extremamente grande ao infinitamente pequeno.\u00a0<\/b><\/span><\/span><\/span><\/p>\n

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

Ondas eletromagn\u00e9ticas \u2013 Defini\u00e7\u00e3o e Hist\u00f3rico<\/b><\/span><\/span><\/span><\/p>\n

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

Surgem<\/b><\/span><\/span><\/span> quando um <\/b><\/span><\/span><\/span>condutor <\/b><\/span><\/span><\/span>que \u00e9 percorrido por <\/b><\/span><\/span><\/span>uma corrente el\u00e9trica origina ao seu redor <\/b><\/span><\/span><\/span>um <\/b><\/span><\/span><\/span>campo magn\u00e9tico que s\u00f3 existe enquanto houver corrente. <\/b><\/span><\/span><\/span><\/p>\n

Assim, um <\/b><\/span><\/span><\/span>campo magn\u00e9tico deve gerar tamb\u00e9m um campo el\u00e9trico. Quando<\/b><\/span><\/span><\/span> um <\/b><\/span><\/span><\/span>desses campos varia,<\/b><\/span><\/span><\/span> o outro <\/b><\/span><\/span><\/span>tamb\u00e9m sofre varia\u00e7\u00e3o. <\/b><\/span><\/span><\/span>Baseado <\/b><\/span><\/span><\/span>nesse fen\u00f4meno, James Clerk Maxwell<\/b><\/span><\/span><\/span> (1831-1879) concluiu que, <\/b><\/span><\/span><\/span>se um campo el\u00e9trico vari\u00e1vel faz surgir um campo magn\u00e9tico vari\u00e1vel, este deve fazer surgir um outro campo el\u00e9trico vari\u00e1vel e assim por diante.<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Esse encadeamento, atrav\u00e9s do espa\u00e7o de campos el\u00e9tricos e magn\u00e9ticos constitui as ondas eletromagn\u00e9ticas.<\/b><\/span><\/span><\/span><\/p>\n

Atrav\u00e9s de seus <\/b><\/span><\/span><\/span>estudos te\u00f3ricos para a fundamenta\u00e7\u00e3o do eletromagnetismo<\/b><\/span><\/span><\/span> Maxwell conseguiu <\/b><\/span><\/span><\/span>obter o valor da velocidade da luz <\/b><\/span><\/span><\/span>(onda eletromagn\u00e9tica) <\/b><\/span><\/span><\/span>no v\u00e1cuo como sendo de v =c = 3,0.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>m\/s.<\/b><\/span><\/span><\/span><\/p>\n

Somente <\/b><\/span><\/span><\/span>oito anos depois da morte de Maxwell, em 1887, Heinrich Rudolf Hertz <\/b><\/span><\/span><\/span>(1857-1894), em uma <\/b><\/span><\/span><\/span>s\u00e9rie de experimentos conseguiu produzir essas ondas eletromagn\u00e9ticas,<\/b><\/span><\/span><\/span> (tamb\u00e9m chamadas \u00a0de ondas hertzianas em sua homenagem) e, <\/b><\/span><\/span><\/span>confirmando as previs\u00f5es te\u00f3ricas de Maxwell, permitiu o nascimento de uma nova era tecnol\u00f3gica: <\/b><\/span><\/span><\/span>a da transmiss\u00e3o de <\/b><\/span><\/span><\/span>informa\u00e7\u00e3o atrav\u00e9s de ondas eletromagn\u00e9ticas. <\/b><\/span><\/span><\/span><\/p>\n

A partir da\u00ed, o <\/b><\/span><\/span><\/span>desenvolvimento das tecnologias permitiu tirar delas todos os imensos benef\u00edcios que hoje desfrutamos e que iremos desfrutar.<\/b><\/span><\/span><\/span><\/p>\n

Efeito fotoel\u00e9trico<\/b><\/span><\/span><\/span><\/p>\n

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

Heinrich Rudolf Hertz, <\/b><\/span><\/span><\/span>em 1887, <\/b><\/span><\/span><\/span>detectou e gerou em laborat\u00f3rio, em uma s\u00e9rie de experi\u00eancias <\/b><\/span><\/span><\/span>que,\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

experi\u00eancias<\/b><\/span><\/span><\/span> que,\u00a0<\/b><\/span><\/span><\/span>quando a luz<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>(onda eletromagn\u00e9tica, radia\u00e7\u00e3o eletromagn\u00e9tica) <\/b><\/span><\/span><\/span>de freq\u00fc\u00eancia suficientemente alta incide sobre a superf\u00edcie de um metal, ela pode retirar el\u00e9trons do mesmo<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

Esse fen\u00f4meno ficou conhecido como<\/b><\/span><\/span><\/span>\u00a0efeito fotoel\u00e9trico.<\/b><\/span><\/span><\/span><\/p>\n

Experi\u00eancias que ilustram o efeito fotoel\u00e9trico<\/b><\/span><\/span><\/span><\/p>\n

\"\" A <\/b><\/span><\/span><\/span>figura abaixo <\/b><\/span><\/span><\/span>ilustra uma <\/b><\/span><\/span><\/span>experi\u00eancia simples <\/b><\/span><\/span><\/span>que permite <\/b><\/span><\/span><\/span>observar o efeito fotoel\u00e9trico. <\/b><\/span><\/span><\/span><\/p>\n

No <\/b><\/span><\/span><\/span>interior da ampola de vidro existe v\u00e1cuo <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>entre as placas A e B existe uma diferen\u00e7a de potencial vari\u00e1vel U =<\/b><\/span><\/span><\/span> <\/b>V<\/b><\/span><\/span><\/span>A<\/b><\/span><\/span><\/sub><\/span>\u00a0\u2013 V<\/b><\/span><\/span><\/span>B<\/b><\/span><\/span><\/sub><\/span>. \u00a0\u00a0<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Sem a incid\u00eancia de radia\u00e7\u00e3o<\/b><\/span><\/span><\/span><\/p>\n

eletromagn\u00e9tica, n\u00e3o existe corrente el\u00e9trica no circuito. <\/b><\/span><\/span><\/span><\/p>\n

Com a incid\u00eancia de radia\u00e7\u00e3o eletromagn\u00e9tica na placa B<\/b><\/span><\/span><\/span>, mantida num <\/b><\/span><\/span><\/span>potencial el\u00e9trico menor que a placa A, <\/b><\/span><\/span><\/span>surge uma <\/b><\/span><\/span><\/span>corrente el\u00e9trica<\/b><\/span><\/span><\/span> (movimento ordenado de el\u00e9trons que s\u00e3o extra\u00eddos da placa B), <\/b><\/span><\/span><\/span>e que \u00e9 medida pelo galvan\u00f4metro (amper\u00edmetro).<\/b><\/span><\/span><\/span><\/p>\n

\"\"\u00a0<\/span>Outra experi\u00eancia simples <\/b><\/span><\/span><\/span>que demonstra a\u00a0<\/b><\/span><\/span><\/span>exist\u00eancia do efeito fotoel\u00e9trico<\/b><\/span><\/span><\/span>\u00a0\"\"<\/b><\/span><\/span><\/span> <\/b>Quando<\/b><\/span><\/span><\/span> um <\/b><\/span><\/span><\/span>bast\u00e3o eletrizado com cargas, <\/b><\/span><\/span><\/span>por exemplo, <\/b><\/span><\/span><\/span>negativas \u00e9 encostado na esfera do eletrosc\u00f3pio que estava neutro <\/b><\/span><\/span><\/span>(hastes fechadas), o <\/b><\/span><\/span><\/span>bast\u00e3o transfere cargas ao eletrosc\u00f3pio, eletrizando-o e abrindo as hastes de determinado \u00e2ngulo.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Em seguida, se <\/b><\/span><\/span><\/span>voc\u00ea fizer incidir radia\u00e7\u00e3o eletromagn\u00e9tica <\/b><\/span><\/span><\/span>(por exemplo, luz) <\/b><\/span><\/span><\/span>sobre a esfera do eletrosc\u00f3pio,<\/b><\/span><\/span><\/span> o <\/b><\/span><\/span><\/span>\u00e2ngulo entre as duas hastes diminui, <\/b><\/span><\/span><\/span>assinalando <\/b><\/span><\/span><\/span>uma diminui\u00e7\u00e3o da carga em excesso no eletrosc\u00f3pio devido \u00e0 emiss\u00e3o de el\u00e9trons causada pelo efeito fotoel\u00e9trico.
\n<\/b><\/span><\/span><\/span><\/p>\n

Explica\u00e7\u00e3o do Efeito Fotoel\u00e9trico<\/b><\/span><\/span><\/span><\/p>\n

\u00a0Foi <\/b><\/span><\/span><\/span>Albert Einstein que explicou corretamente o efeito fotoel\u00e9trico <\/b><\/span><\/span><\/span>em 1921, <\/b><\/span><\/span><\/span>recebendo<\/b><\/span><\/span><\/span> por isso o <\/b><\/span><\/span><\/span>pr\u00eamio Nobel da F\u00edsica.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Segundo <\/b><\/span><\/span><\/span>Einstein a energia de qualquer radia\u00e7\u00e3o luminosa <\/b><\/span><\/span><\/span>(inclusive luz) <\/b><\/span><\/span><\/span>n\u00e3o se espalha uniforme e continuamente pelo espa\u00e7o mas, sim, concentrada em pequenos \u201cpacotes\u201dque carregam uma quantidade bem definida de energia. <\/b><\/span><\/span><\/span><\/p>\n

Cada um desses pacotes <\/b><\/span><\/span><\/span>\u00e9 denominado\u00a0<\/b><\/span><\/span><\/span>quantum<\/b><\/span><\/span><\/span>\u00a0de<\/b><\/span><\/span><\/span> <\/b>energia<\/b><\/span><\/span><\/span> e esse <\/b><\/span><\/span><\/span>modelo constru\u00eddo por Einstein <\/b><\/span><\/span><\/span>recebeu o nome de\u00a0<\/b><\/span><\/span><\/span>teoria\u00a0 dos quanta.<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Quanta,<\/b><\/span><\/span><\/span> em latim \u00e9 <\/b><\/span><\/span><\/span>plural de quantum, <\/b><\/span><\/span><\/span>que significa <\/b><\/span><\/span><\/span>\u201cquantidade\u201d.<\/b><\/span><\/span><\/span><\/p>\n

Esses<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>quanta\u00a0<\/b><\/span><\/span><\/span>de energia radiante<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>foram denominados <\/b><\/span><\/span><\/span>de f\u00f3tons.<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>f\u00f3ton, <\/b><\/span><\/span><\/span>como qualquer part\u00edcula, possui uma <\/b><\/span><\/span><\/span>certa energia (W), <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>rela\u00e7\u00e3o energia (W)<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>frequ\u00eancia (f), <\/b><\/span><\/span><\/span>\u00e9 proporcional<\/b><\/span><\/span><\/span> <\/b>e est\u00e1 <\/b><\/span><\/span><\/span>relacionada por uma constante, a <\/b><\/span><\/span><\/span>constante de Planck<\/b><\/span><\/span><\/span> (h).<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Observa\u00e7\u00f5es:<\/b><\/span><\/span><\/span><\/p>\n

\"\" el\u00e9tron-volt <\/b><\/span><\/span><\/span>(eV) <\/b><\/span><\/span><\/span>e joule <\/b><\/span><\/span><\/span>(J) <\/b><\/span><\/span><\/span>s\u00e3o <\/b><\/span><\/span><\/span>unidades de energia <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>rela\u00e7\u00e3o<\/b><\/span><\/span><\/span> entre elas \u00e9 <\/b><\/span><\/span><\/span>1 eV = 1,6.10<\/b><\/span><\/span><\/span>-19<\/b><\/span><\/span><\/sup><\/span> J. <\/b><\/span><\/span><\/span>
\n<\/b><\/span><\/span><\/span><\/p>\n

\"\" A equa\u00e7\u00e3o <\/b><\/span><\/span><\/span>W = h.f <\/b><\/span><\/span><\/span>\u00e9 usada para <\/b><\/span><\/span><\/span>calcular<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>energia de um f\u00f3ton <\/b><\/span><\/span><\/span>quando \u00e9 dada a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia.<\/b><\/span><\/span><\/span> Nessa equa\u00e7\u00e3o a <\/b><\/span><\/span><\/span>energia W \u00e9 calculada em joule (J) <\/b><\/span><\/span><\/span>quando o <\/b><\/span><\/span><\/span>valor de h \u00e9 substitu\u00eddo por h = 6,63.<\/b><\/span><\/span><\/span><\/p>\n

10<\/b><\/span><\/span><\/span>-34 <\/b><\/span><\/span><\/sup><\/span>J.s <\/b><\/span><\/span><\/span>e, em <\/b><\/span><\/span><\/span>el\u00e9tron-volt (eV) quando a constante de Planck h \u00e9 substitu\u00edda por h = 4,14.10<\/b><\/span><\/span><\/span>-15<\/b><\/span><\/span><\/sup><\/span> eV. <\/b><\/span><\/span><\/span><\/p>\n

\"\" A <\/b><\/span><\/span><\/span>velocidade<\/b><\/span><\/span><\/span> de uma <\/b><\/span><\/span><\/span>onda (part\u00edcula, f\u00f3ton) <\/b><\/span><\/span><\/span>\u00e9 <\/b><\/span><\/span><\/span>calculada por v = c = \u03bbf \"\" <\/b><\/span><\/span><\/span>isolando a frequ\u00eancia <\/b><\/span><\/span><\/span>f = v\/\u03bb <\/b><\/span><\/span><\/span>e <\/b><\/span><\/span><\/span>substituindo na equa\u00e7\u00e3o da energia (W = hf) <\/b><\/span><\/span><\/span>voc\u00ea ir\u00e1 encontrar uma <\/b><\/span><\/span><\/span>nova express\u00e3o <\/b><\/span><\/span><\/span>para o c\u00e1lculo da <\/b><\/span><\/span><\/span>energia (W) <\/b><\/span><\/span><\/span>em fun\u00e7\u00e3o do <\/b><\/span><\/span><\/span>comprimento de onda (\u03bb\"\"<\/b><\/span><\/span><\/span><\/p>\n

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

Condi\u00e7\u00f5es para que ocorra o efeito fotoel\u00e9trico<\/span><\/span><\/span><\/p>\n

Como j\u00e1 vimos, o <\/b><\/span><\/span><\/span>efeito fotoel\u00e9trico \u00e9 interpretado como a absor\u00e7\u00e3o de um f\u00f3ton pela mat\u00e9ria, levando \u00e0 eje\u00e7\u00e3o de um el\u00e9tron.<\/b><\/span><\/span><\/span><\/p>\n

Os <\/b><\/span><\/span><\/span>el\u00e9trons que giram \u00e0 volta do n\u00facleo s\u00e3o a\u00ed mantidos por for\u00e7as de atra\u00e7\u00e3o. <\/b><\/span><\/span><\/span><\/p>\n

Se eles <\/b><\/span><\/span><\/span>receberem energia suficiente <\/b><\/span><\/span><\/span>(energia m\u00ednima de extra\u00e7\u00e3o), <\/b><\/span><\/span><\/span>eles abandonar\u00e3o as suas \u00f3rbitas.<\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>efeito fotoel\u00e9trico s\u00f3 surge se o metal receber um feixe de radia\u00e7\u00e3o <\/b><\/span><\/span><\/span>com <\/b><\/span><\/span><\/span>energia superior <\/b><\/span><\/span><\/span>\u00e0 <\/b><\/span><\/span><\/span>energia m\u00ednima de remo\u00e7\u00e3o dos el\u00e9trons <\/b><\/span><\/span><\/span>do metal, <\/b><\/span><\/span><\/span>provocando a <\/b><\/span><\/span><\/span>sua sa\u00edda das \u00f3rbitas <\/b><\/span><\/span><\/span>o que <\/b><\/span><\/span><\/span>pode ocorrer sem energia cin\u00e9tica<\/b><\/span><\/span><\/span> (se a energia da radia\u00e7\u00e3o for igual \u00e0 energia de remo\u00e7\u00e3o) ou <\/b><\/span><\/span><\/span>com energia cin\u00e9tica,( <\/b><\/span><\/span><\/span>se a energia da radia\u00e7\u00e3o exceder a energia de remo\u00e7\u00e3o dos el\u00e9trons).<\/b><\/span><\/span><\/span><\/p>\n

Essa\u00a0<\/b><\/span><\/span><\/span>energia m\u00ednima (W<\/b><\/span><\/span><\/span>min<\/b><\/span><\/span><\/sub><\/span>)<\/b><\/span><\/span><\/span> para <\/b><\/span><\/span><\/span>extrair um el\u00e9tron\u00a0<\/b><\/span><\/span><\/span>da placa met\u00e1lica<\/b><\/span><\/span><\/span> \u00e9 <\/b><\/span><\/span><\/span>denominada\u00a0<\/b><\/span><\/span><\/span>fun\u00e7\u00e3o<\/b><\/span><\/span><\/span> <\/b>trabalho<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>e est\u00e1 <\/b><\/span><\/span><\/span>relacionada com o tipo de metal utilizado.<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Se a <\/b><\/span><\/span><\/span>energia do f\u00f3ton que incide (W = h.f)<\/b><\/span><\/span><\/span> <\/b>for maior que a fun\u00e7\u00e3o trabalho (W<\/b><\/span><\/span><\/span>min<\/b><\/span><\/span><\/sub><\/span>)<\/b><\/span><\/span><\/span> <\/b>a <\/b><\/span><\/span><\/span>energia<\/b><\/span><\/span><\/span> em <\/b><\/span><\/span><\/span>excesso ser\u00e1 <\/b><\/span><\/span><\/span>energia cin\u00e9tica (E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>),<\/b><\/span><\/span><\/span> <\/b>de modo que\u00a0 \"\" <\/b><\/span><\/span><\/span>W<\/b><\/span><\/span><\/span>min<\/b><\/span><\/span><\/sub><\/span> = W \u2013 Ec \u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>W<\/b><\/span><\/span><\/span>min<\/b><\/span><\/span><\/sub><\/span> = h.f \u2013 E<\/b><\/span><\/span><\/span>c \"\"<\/b><\/span><\/span><\/sub><\/span><\/p>\n

(equa\u00e7\u00e3o fotoel\u00e9trica de Einstein).<\/b><\/span><\/span><\/span><\/p>\n

\"\"\"\"<\/p>\n

Da equa\u00e7\u00e3o W = h.f \"\" f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> = W\/h \"\" f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> \u00e9 a frequ\u00eancia m\u00ednima (frequ\u00eancia de corte) a partir da qual os el\u00e9trons s\u00e3o extra\u00eddos do metal.<\/b><\/span><\/span><\/span><\/p>\n

Assim, nenhum el\u00e9tron \u00e9 emitido pelo metal enquanto a frequ\u00eancia da luz (f\u00f3tons) incidente n\u00e3o ultrapassar um certo limite de frequ\u00eancia, denominada frequ\u00eancia de corte (f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>).<\/b><\/span><\/span><\/span><\/p>\n

Gr\u00e1fico da energia cin\u00e9tica do el\u00e9tron extra\u00eddo em fun\u00e7\u00e3o da frequ\u00eancia da radia\u00e7\u00e3o do (f\u00f3ton, luz) incidente<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>figura ao lado <\/b><\/span><\/span><\/span>mostra o <\/b><\/span><\/span><\/span>gr\u00e1fico da energia cin\u00e9tica do el\u00e9tron extra\u00eddo <\/b><\/span><\/span><\/span>em fun\u00e7\u00e3o da <\/b><\/span><\/span><\/span>frequ\u00eancia da radia\u00e7\u00e3o do f\u00f3ton (luz) incidente, <\/b><\/span><\/span><\/span>para uma <\/b><\/span><\/span><\/span>mesma placa met\u00e1lica (c\u00e9lula fotoel\u00e9trica).<\/b><\/span><\/span><\/span>\"\"<\/p>\n

f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0\u00e9 a frequ\u00eancia m\u00ednima (frequ\u00eancia de corte) necess\u00e1ria<\/b><\/span><\/span><\/span> para <\/b><\/span><\/span><\/span>produzir o efeito fotoel\u00e9trico. <\/b><\/span><\/span><\/span><\/p>\n

Se <\/b><\/span><\/span><\/span>f = f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>el\u00e9tron \u00e9 liberado, <\/b><\/span><\/span><\/span>mas <\/b><\/span><\/span><\/span>sua energia cin\u00e9tica \u00e9 nula. <\/b><\/span><\/span><\/span><\/p>\n

Para <\/b><\/span><\/span><\/span>frequ\u00eancias inferiores a f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> <\/b>o <\/b><\/span><\/span><\/span>fen\u00f4meno n\u00e3o ocorre (nenhum el\u00e9tron \u00e9 liberado). <\/b><\/span><\/span><\/span><\/p>\n

Por\u00e9m, para <\/b><\/span><\/span><\/span>valores superiores a f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>, o n\u00famero de el\u00e9trons arrancados \u00e9 diretamente proporcional<\/b><\/span><\/span><\/span> \u00e0 <\/b><\/span><\/span><\/span>intensidade da radia\u00e7\u00e3o eletromagn\u00e9tica incidente, <\/b><\/span><\/span><\/span>ou seja, <\/b><\/span><\/span><\/span>aumentando a intensidade \u201cn\u00famero\u201d da radia\u00e7\u00e3o incidente <\/b><\/span><\/span><\/span>no metal<\/b><\/span><\/span><\/span>, aumenta-se <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>n\u00edvel energ\u00e9tico dos f\u00f3tons incidentes, aumentando<\/b><\/span><\/span><\/span> assim o <\/b><\/span><\/span><\/span>n\u00famero de el\u00e9trons arrancados.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Observe <\/b><\/span><\/span><\/span>no gr\u00e1fico <\/b><\/span><\/span><\/span>que, para a <\/b><\/span><\/span><\/span>mesma placa (mesma frerqu\u00eancia de corte f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>),<\/b><\/span><\/span><\/span> <\/b>\u00e0 medida <\/b><\/span><\/span><\/span>que a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia da radia\u00e7\u00e3o incidente aumenta<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>energia cin\u00e9tica dos el\u00e9trons emitidos tamb\u00e9m aumenta<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

Mas, para a <\/b><\/span><\/span><\/span>mesma freq\u00fc\u00eancia f,<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>energia cin\u00e9tica dos el\u00e9trons emitidos \u00e9 sempre a mesma, <\/b><\/span><\/span><\/span>pois, <\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>= hf \u2013 W = <\/b><\/span><\/span><\/span>h.f \u2013 h.f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0 = constante<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0\u2013 constante<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sub><\/span>= constante.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Aumentando-se a intensidade <\/b><\/span><\/span><\/span>da <\/b><\/span><\/span><\/span>radia\u00e7\u00e3o incidente<\/b><\/span><\/span><\/span>, isto \u00e9, <\/b><\/span><\/span><\/span>aumentando-se o n\u00famero de f\u00f3tons incidentes,<\/b><\/span><\/span><\/span> <\/b>aumenta o n\u00famero de el\u00e9trons emitidos (figura acima) sem alterar a energia cin\u00e9tica m\u00e1xima deles.<\/b><\/span><\/span><\/span><\/p>\n

Abaixo de\u00a0<\/b><\/span><\/span><\/span>f<\/b><\/i><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0n\u00e3o h\u00e1 emiss\u00e3o de el\u00e9trons, <\/b><\/span><\/span><\/span>independentemente da <\/b><\/span><\/span><\/span>intensidade da radia\u00e7\u00e3o incidente.<\/b><\/span><\/span><\/span><\/p>\n

Algumas das muitas utilidades pr\u00e1ticas do efeito fotoel\u00e9trico<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

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

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

Dualidade da luz<\/b><\/span><\/span><\/span><\/p>\n

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

Quando a <\/b><\/span><\/span><\/span>luz interage com a mat\u00e9ria <\/b><\/span><\/span><\/span>atrav\u00e9s de absor\u00e7\u00e3o, emiss\u00e3o, choques, etc.<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>ela se <\/b><\/span><\/span><\/span>comporta como <\/b><\/span><\/span><\/span>part\u00edcula<\/b><\/span><\/span><\/span>,<\/b><\/span><\/span><\/span> <\/b>mas para os fen\u00f4menos referentes \u00e0 sua propaga\u00e7\u00e3o, reflex\u00e3o, refra\u00e7\u00e3o,<\/b><\/span><\/span><\/span> <\/b>interfer\u00eancia, etc<\/b><\/span><\/span><\/span>., ela se <\/b><\/span><\/span><\/span>comporta como onda.<\/b><\/span><\/span><\/span><\/p>\n

\u00a0O f\u00edsico franc\u00eas <\/b><\/span><\/span><\/span>Louis de Broglie <\/b><\/span><\/span><\/span>apresentou, em 1924, a seguinte <\/b><\/span><\/span><\/span>hip\u00f3tese que, <\/b><\/span><\/span><\/span>depois, em 1927 <\/b><\/span><\/span><\/span>foi comprovada experimentalmente: <\/b><\/span><\/span><\/span>\u201cpart\u00edculas tamb\u00e9m possuem propriedades ondulat\u00f3rias\u201d<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Das equa\u00e7\u00f5es E = W = m.c<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"\u00a0 c \"\" velocidade da luz no v\u00e1cuo\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>W = h.f\u00a0<\/b><\/span><\/span><\/span> \"\"\u00a0 <\/b><\/span><\/span><\/span>c = \u03bbf\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 f = c\/\u03bb \"\"<\/b><\/span><\/span><\/span><\/p>\n

mc<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sup><\/span>= hf\u00a0 \"\"\u00a0 mc<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sup><\/span>= h(c\/\u03bb)\u00a0 \"\"\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u03bb = h\/mc<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u00a0\"\"\u00a0 <\/b><\/span><\/span><\/span>mc = Q \"\" quantidade de movimento \"\"<\/b><\/span><\/span><\/span> <\/b>\u03bb = h\/Q<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

Nessa express\u00e3o <\/b><\/span><\/span><\/span>\u03bb = h\/Q<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u00a0, como <\/b><\/span><\/span><\/span>h \u00e9 constante, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>quantidade de movimento Q = mV evidencia\u00a0o car\u00e1ter corpuscular da luz (m \u00e9 massa da particula) <\/b><\/span><\/span><\/span>enquanto que o <\/b><\/span><\/span><\/span>comprimento de onda \u03bb evidencia seu car\u00e1ter ondulat\u00f3rio.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

As naturezas ondulat\u00f3ria e corpuscular da luz s\u00e3o complementares e n\u00e3o antag\u00f4nicas<\/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

\"\"<\/p>\n

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

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

Observe na <\/b><\/span><\/span><\/span>tabela ao lado <\/b><\/span><\/span><\/span>que a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia e consequentemente o n\u00edvel de energia dos f\u00f3tons incidentes <\/b><\/span><\/span><\/span>aumenta do <\/b><\/span><\/span><\/span>vermelho para o violeta.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

A equa\u00e7\u00e3o <\/b><\/span><\/span><\/span>W = h.f <\/b><\/span><\/span><\/span>\u00e9 usada para <\/b><\/span><\/span><\/span>calcular<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>energia de um f\u00f3ton <\/b><\/span><\/span><\/span>quando \u00e9 dada a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia.<\/b><\/span><\/span><\/span> Nessa equa\u00e7\u00e3o a <\/b><\/span><\/span><\/span>energia W \u00e9 calculada em joule (J) <\/b><\/span><\/span><\/span>quando o <\/b><\/span><\/span><\/span>valor de h \u00e9 substitu\u00eddo por h = 6,63.<\/b><\/span><\/span><\/span><\/p>\n

10<\/b><\/span><\/span><\/span>-34 <\/b><\/span><\/span><\/sup><\/span>J.s <\/b><\/span><\/span><\/span>e, em <\/b><\/span><\/span><\/span>el\u00e9tron-volt (eV) quando a constante de Planck h \u00e9 substitu\u00edda por h = 4,14.10<\/b><\/span><\/span><\/span>-15<\/b><\/span><\/span><\/sup><\/span> eV. <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

el\u00e9tron-volt <\/b><\/span><\/span><\/span>(eV) <\/b><\/span><\/span><\/span>e joule <\/b><\/span><\/span><\/span>(J) <\/b><\/span><\/span><\/span>s\u00e3o <\/b><\/span><\/span><\/span>unidades de energia <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>rela\u00e7\u00e3o<\/b><\/span><\/span><\/span> entre elas \u00e9 <\/b><\/span><\/span><\/span>1 eV = 1,6.10<\/b><\/span><\/span><\/span>-19<\/b><\/span><\/span><\/sup><\/span> J. <\/b><\/span><\/span><\/span>
\n<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>figura ao lado <\/b><\/span><\/span><\/span>mostra o <\/b><\/span><\/span><\/span>gr\u00e1fico da energia cin\u00e9tica do el\u00e9tron extra\u00eddo <\/b><\/span><\/span><\/span>em fun\u00e7\u00e3o da <\/b><\/span><\/span><\/span>frequ\u00eancia da radia\u00e7\u00e3o do f\u00f3ton (luz) incidente, <\/b><\/span><\/span><\/span>para uma <\/b><\/span><\/span><\/span>mesma placa met\u00e1lica (c\u00e9lula fotoel\u00e9trica).<\/b><\/span><\/span><\/span>\"\"<\/p>\n

f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0\u00e9 a frequ\u00eancia m\u00ednima (frequ\u00eancia de corte) necess\u00e1ria<\/b><\/span><\/span><\/span> para <\/b><\/span><\/span><\/span>produzir o efeito fotoel\u00e9trico. <\/b><\/span><\/span><\/span><\/p>\n

Se <\/b><\/span><\/span><\/span>f = f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>el\u00e9tron \u00e9 liberado, <\/b><\/span><\/span><\/span>mas <\/b><\/span><\/span><\/span>sua energia cin\u00e9tica \u00e9 nula. <\/b><\/span><\/span><\/span><\/p>\n

Para <\/b><\/span><\/span><\/span>frequ\u00eancias inferiores a f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> <\/b>o <\/b><\/span><\/span><\/span>fen\u00f4meno n\u00e3o ocorre (nenhum el\u00e9tron \u00e9 liberado). <\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Os <\/b><\/span><\/span><\/span>el\u00e9trons s\u00e3o emitidos imediatamente. N\u00e3o existe atraso de tempo entre a incid\u00eancia <\/b><\/span><\/span><\/span>da luz e a <\/b><\/span><\/span><\/span>emiss\u00e3o dos el\u00e9trons.
\n<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Para <\/b><\/span><\/span><\/span>valores superiores a f<\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/sub><\/span>(frequ\u00eancia de corte), o n\u00famero de el\u00e9trons arrancados \u00e9 diretamente proporcional<\/b><\/span><\/span><\/span> \u00e0 <\/b><\/span><\/span><\/span>intensidade da radia\u00e7\u00e3o eletromagn\u00e9tica incidente, <\/b><\/span><\/span><\/span>ou seja, <\/b><\/span><\/span><\/span>aumentando a intensidade \u201cn\u00famero\u201d da radia\u00e7\u00e3o incidente <\/b><\/span><\/span><\/span>no metal<\/b><\/span><\/span><\/span>, aumenta-se <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>n\u00edvel energ\u00e9tico dos f\u00f3tons incidentes, aumentando<\/b><\/span><\/span><\/span> assim o <\/b><\/span><\/span><\/span>n\u00famero de el\u00e9trons arrancados.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

\"\"<\/p>\n

Da equa\u00e7\u00e3o W = h.f \"\" f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> = W\/h \"\" f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span> \u00e9 a frequ\u00eancia m\u00ednima (frequ\u00eancia de corte) a partir da qual os el\u00e9trons s\u00e3o extra\u00eddos do metal.<\/b><\/span><\/span><\/span><\/p>\n

Assim, nenhum el\u00e9tron \u00e9 emitido pelo metal enquanto a frequ\u00eancia da luz (f\u00f3tons) incidente n\u00e3o ultrapassar um certo limite de frequ\u00eancia, denominada frequ\u00eancia de corte (f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>).<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Observe <\/b><\/span><\/span><\/span>no gr\u00e1fico <\/b><\/span><\/span><\/span>que, para a <\/b><\/span><\/span><\/span>mesma placa (mesma frerqu\u00eancia de corte f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>),<\/b><\/span><\/span><\/span> <\/b>\u00e0 medida <\/b><\/span><\/span><\/span>que a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia da radia\u00e7\u00e3o incidente aumenta<\/b><\/span><\/span><\/span>, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>energia cin\u00e9tica dos el\u00e9trons emitidos tamb\u00e9m aumenta<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

Mas, para a <\/b><\/span><\/span><\/span>mesma freq\u00fc\u00eancia f,<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>energia cin\u00e9tica dos el\u00e9trons emitidos \u00e9 sempre a mesma, <\/b><\/span><\/span><\/span>pois, <\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>c<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>= hf \u2013 W = <\/b><\/span><\/span><\/span>h.f \u2013 h.f<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0 = constante<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0\u2013 constante<\/b><\/span><\/span><\/span>2 <\/b><\/span><\/span><\/sub><\/span>= constante.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

Aumentando-se a intensidade <\/b><\/span><\/span><\/span>da <\/b><\/span><\/span><\/span>radia\u00e7\u00e3o incidente<\/b><\/span><\/span><\/span>, isto \u00e9, <\/b><\/span><\/span><\/span>aumentando-se o n\u00famero de f\u00f3tons incidentes,<\/b><\/span><\/span><\/span> <\/b>aumenta o n\u00famero de el\u00e9trons emitidos (figura acima) sem alterar a energia cin\u00e9tica m\u00e1xima deles.<\/b><\/span><\/span><\/span><\/p>\n

Abaixo de\u00a0<\/b><\/span><\/span><\/span>f<\/b><\/i><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0n\u00e3o h\u00e1 emiss\u00e3o de el\u00e9trons, <\/b><\/span><\/span><\/span>independentemente da <\/b><\/span><\/span><\/span>intensidade da radia\u00e7\u00e3o incidente.<\/b><\/span><\/span><\/span><\/p>\n

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

\"\"<\/p>\n

A<\/b><\/span><\/span><\/span> emiss\u00e3o e a energia \u00a0dos el\u00e9trons arrancados <\/b><\/span><\/span><\/span>dependem da <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia e n\u00e3o da intensidade da <\/b><\/span><\/span><\/span><\/p>\n

radia\u00e7\u00e3o eletromagn\u00e9tica incidente.<\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>energia cin\u00e9tica m\u00e1xima <\/b><\/span><\/span><\/span>\u00e9 fornecida pela <\/b><\/span><\/span><\/span>express\u00e3o E<\/b><\/span><\/span><\/span>c <\/b><\/span><\/span><\/sub><\/span>= e.V<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/sub><\/span>\u00a0<\/b><\/span><\/span><\/span>(<\/b><\/span><\/span><\/span>e \"\"<\/b><\/span><\/span><\/span> carga de 1 el\u00e9tron e <\/b><\/span><\/span><\/span>V<\/b><\/span><\/span><\/span>o \"\"<\/b><\/span><\/span><\/sub><\/span> potencial de corte)<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>potencial de corte <\/b><\/span><\/span><\/span>\u00e9 o mesmo <\/b><\/span><\/span><\/span>qualquer que seja a intensidade da radia\u00e7\u00e3o eletromagn\u00e9tica incidente.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>energia cin\u00e9tica do el\u00e9tron <\/b><\/span><\/span><\/span>emitido \u00e9 <\/b><\/span><\/span><\/span>dada pela equa\u00e7\u00e3o Ec = mv\u00b2\/2 = hf \u2013 W, <\/b><\/span><\/span><\/span>em que o <\/b><\/span><\/span><\/span>termo hf <\/b><\/span><\/span><\/span>\u00e9 a <\/b><\/span><\/span><\/span>energia cedida ao el\u00e9tron pela luz, <\/b><\/span><\/span><\/span>sendo <\/b><\/span><\/span><\/span>h a constante de Planck e f a frequ\u00eancia da luz incidente. <\/b><\/span><\/span><\/span><\/p>\n

O <\/b><\/span><\/span><\/span>termo<\/b><\/span><\/span><\/span>\u00a0W<\/b><\/span><\/span><\/span>\u00a0\u00e9 a <\/b><\/span><\/span><\/span>energia que o el\u00e9tron tem que adquirir para poder sair do material, <\/b><\/span><\/span><\/span>e \u00e9 chamado<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>fun\u00e7\u00e3o trabalho\u00a0<\/b><\/span><\/span><\/span>do metal.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

Sendo <\/b><\/span><\/span><\/span>c <\/b><\/span><\/span><\/span>a<\/b><\/span><\/span><\/span> velocidade da luz no v\u00e1cuo (c=3,0.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>m\/s), \u03bb <\/b><\/span><\/span><\/span>o <\/b><\/span><\/span><\/span>comprimento de onda da radia\u00e7\u00e3o <\/b><\/span><\/span><\/span>(luz) do <\/b><\/span><\/span><\/span>f\u00f3ton incidente<\/b><\/span><\/span><\/span> e <\/b><\/span><\/span><\/span>f <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>freq\u00fc\u00eancia da onda (luz, el\u00e9trons) emitida, tem-se\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 c = \u03bbf\u00a0 \"\"\u00a0 W = hf \"\"\u00a0<\/b><\/span><\/span><\/span>W = h.(c\/\u03bb).<\/b><\/span><\/span><\/span><\/p>\n

Observe na express\u00e3o <\/b><\/span><\/span><\/span>W = h.(c\/\u03bb)<\/b><\/span><\/span><\/span> <\/b>que, como <\/b><\/span><\/span><\/span>h e C s\u00e3o constantes, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>energia do f\u00f3ton <\/b><\/span><\/span><\/span>(quantum) <\/b><\/span><\/span><\/span>necess\u00e1ria para liberar el\u00e9trons (emitir luz) \u00e9 inversamente proporcional ao comprimento de onda.\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

Assim, como, por exemplo, a <\/b><\/span><\/span><\/span>cor vermelha tem baixa freq\u00fc\u00eancia <\/b><\/span><\/span><\/span>(ou grande comprimento de onda \u03bb), <\/b><\/span><\/span><\/span>os f\u00f3tons de luz vermelha t\u00eam baixa energia e n\u00e3o conseguem arrancar el\u00e9trons. <\/b><\/span><\/span><\/span><\/p>\n

Mas, a <\/b><\/span><\/span><\/span>cor azul <\/b><\/span><\/span><\/span>(pequeno comprimento de onda e grande frequ\u00eancia), <\/b><\/span><\/span><\/span>possui mais energia e consegue arrancar el\u00e9trons.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0<\/span>A luz tem car\u00e1ter dual:<\/b><\/span><\/span><\/span> Quando a <\/b><\/span><\/span><\/span>luz interage com a mat\u00e9ria <\/b><\/span><\/span><\/span>atrav\u00e9s de <\/b><\/span><\/span><\/span>absor\u00e7\u00e3o, emiss\u00e3o, choques, etc., ela se comporta como part\u00edcula,<\/b><\/span><\/span><\/span> <\/b>mas para <\/b><\/span><\/span><\/span>os fen\u00f4menos referentes \u00e0 sua propaga\u00e7\u00e3o, reflex\u00e3o, refra\u00e7\u00e3o, interfer\u00eancia, etc., ela se comporta como onda.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

\"\"<\/p>\n

“De <\/b><\/span><\/span><\/span>acordo com a teoria formulada<\/b><\/span><\/span><\/span> em 1900 pelo <\/b><\/span><\/span><\/span>f\u00edsico alem\u00e3o Max Planck, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>mat\u00e9ria emite ou <\/b><\/span><\/span><\/span><\/p>\n

absorve energia eletromagn\u00e9tica <\/b><\/span><\/span><\/span>de maneira <\/b><\/span><\/span><\/span>descont\u00ednua<\/b><\/span><\/span><\/span> <\/b>emitindo ou absorvendo <\/b><\/span><\/span><\/span>f\u00f3tons,<\/b><\/span><\/span><\/span> cuja <\/b><\/span><\/span><\/span>energia \u00e9 proporcional <\/b><\/span><\/span><\/span>\u00e0 <\/b><\/span><\/span><\/span>frequ\u00eancia<\/b><\/span><\/span><\/span> da <\/b><\/span><\/span><\/span>radia\u00e7\u00e3o eletromagn\u00e9tica envolvida nessa troca de energia.”<\/b><\/span><\/span><\/span><\/p>\n

Alguns exerc\u00edcios interessantes a que conv\u00e9m conferir as resolu\u00e7\u00f5es<\/b><\/span><\/span><\/span><\/p>\n

01-(UFRN)<\/b><\/span><\/span><\/span> <\/b>B\u00e1rbara <\/b><\/span><\/span><\/span>ficou encantada com a maneira de Natasha <\/b><\/span><\/span><\/span>explicar <\/b><\/span><\/span><\/span>a dualidade onda-part\u00edcula, <\/b><\/span><\/span><\/span>apresentada nos textos de <\/b><\/span><\/span><\/span>F\u00edsica Moderna.<\/b><\/span><\/span><\/span><\/p>\n

Natasha <\/b><\/span><\/span><\/span>fez uma <\/b><\/span><\/span><\/span>analogia com o processo de percep\u00e7\u00e3o de imagens, <\/b><\/span><\/span><\/span>apresentando uma <\/b><\/span><\/span><\/span>explica\u00e7\u00e3o<\/b><\/span><\/span><\/span> <\/b>baseada <\/b><\/span><\/span><\/span>numa figura muito utilizada pelos <\/b><\/span><\/span><\/span>psic\u00f3logos da Gestalt. <\/b><\/span><\/span><\/span><\/p>\n

Seus esclarecimentos <\/b><\/span><\/span><\/span>e a <\/b><\/span><\/span><\/span>figura ilustrativa s\u00e3o reproduzidos <\/b><\/span><\/span><\/span>a seguir:<\/b><\/span><\/span><\/span><\/p>\n

Figura citada por Natasha, <\/b><\/span><\/span><\/span>na qual <\/b><\/span><\/span><\/span>dois perfis formam um c\u00e1lice e vice-versa.<\/b><\/span><\/span><\/span>\"\"<\/p>\n

A <\/b><\/span><\/span><\/span>minha imagem preferida <\/b><\/span><\/span><\/span>sobre o <\/b><\/span><\/span><\/span>comportamento dual da luz <\/b><\/span><\/span><\/span>\u00e9 o desenho de um <\/b><\/span><\/span><\/span>c\u00e1lice feito por dois perfis. <\/b><\/span><\/span><\/span><\/p>\n

Qual a realidade que percebemos na figura? <\/b><\/span><\/span><\/span>Podemos ver um <\/b><\/span><\/span><\/span>c\u00e1lice ou dois perfis, dependendo de <\/b><\/span><\/span><\/span>quem <\/b><\/span><\/span><\/span>consideramos como figura <\/b><\/span><\/span><\/span>e qual <\/b><\/span><\/span><\/span>consideraremos como fundo<\/b><\/span><\/span><\/span>, mas <\/b><\/span><\/span><\/span>n\u00e3o podemos ver ambos<\/b><\/span><\/span><\/span> <\/b>simultaneamente.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\u00c9 um <\/b><\/span><\/span><\/span>exemplo perfeito de realidade criada pelo observador, <\/b><\/span><\/span><\/span>em que <\/b><\/span><\/span><\/span>n\u00f3s decidimos o que vamos observar<\/b><\/span><\/span><\/span>. <\/b><\/span><\/span><\/span><\/p>\n

A <\/b><\/span><\/span><\/span>luz se comporta de forma an\u00e1loga, <\/b><\/span><\/span><\/span>pois, <\/b><\/span><\/span><\/span>dependendo do tipo de experi\u00eancia (“fundo”), revela sua natureza de onda ou sua natureza de part\u00edcula, sempre escondendo uma quando a outra \u00e9 mostrada<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

Diante das <\/b><\/span><\/span><\/span>explica\u00e7\u00f5es acima, \u00e9 correto afirmar que Natasha estava ilustrando, com o comportamento da luz, o que os f\u00edsicos chamam de princ\u00edpio da:<\/b><\/span><\/span><\/span><\/p>\n

a) incerteza de Heisenberg.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

b) complementaridade de Bohr.\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

c) superposi\u00e7\u00e3o.\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0<\/b><\/span><\/span><\/span><\/p>\n

d) relatividade.<\/b><\/span><\/span><\/span><\/p>\n

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

As <\/b><\/span><\/span><\/span>naturezas ondulat\u00f3ria e corpuscular da luz s\u00e3o complementares e n\u00e3o antag\u00f4nicas\u00a0 \"\" <\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>R- B<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span><\/p>\n

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

02-(UFMG-MG)<\/b><\/span><\/span><\/span> <\/b>Em <\/b><\/span><\/span><\/span>alguns laborat\u00f3rios de pesquisa<\/b><\/span><\/span><\/span>, s\u00e3o <\/b><\/span><\/span><\/span>produzidas antipart\u00edculas de part\u00edculas fundamentais da natureza. <\/b><\/span><\/span><\/span>Cite-se, <\/b><\/span><\/span><\/span>como exemplo<\/b><\/span><\/span><\/span>, a <\/b><\/span><\/span><\/span>antipart\u00edcula do el\u00e9tron <\/b><\/span><\/span><\/span>– <\/b><\/span><\/span><\/span>o p\u00f3sitron -, <\/b><\/span><\/span><\/span>que tem a <\/b><\/span><\/span><\/span>mesma massa que o el\u00e9tron e carga de mesmo m\u00f3dulo, por\u00e9m positiva. Quando um p\u00f3sitron<\/b><\/span><\/span><\/span> e um <\/b><\/span><\/span><\/span>el\u00e9tron interagem, ambos podem desaparecer, produzindo dois f\u00f3tons de mesma energia.<\/b><\/span><\/span><\/span> <\/b><\/p>\n

Esse <\/b><\/span><\/span><\/span>fen\u00f4meno<\/b><\/span><\/span><\/span> \u00e9 chamado de <\/b><\/span><\/span><\/span>aniquila\u00e7\u00e3o.<\/b><\/span><\/span><\/span> Com base <\/b><\/span><\/span><\/span>nessas informa\u00e7\u00f5es,<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

a)<\/b><\/span><\/span><\/span> Explique o <\/b><\/span><\/span><\/span>que acontece com a massa do el\u00e9tron e com a do p\u00f3sitron no processo de aniquila\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

Considere que <\/b><\/span><\/span><\/span>tanto o el\u00e9tron quanto o p\u00f3sitron est\u00e3o em repouso.<\/b><\/span><\/span><\/span><\/p>\n

b) <\/b><\/span><\/span><\/span>Calcule a <\/b><\/span><\/span><\/span>frequ\u00eancia dos f\u00f3tons produzidos no processo de aniquila\u00e7\u00e3o.<\/b><\/span><\/span><\/span><\/p>\n

Dado que a <\/b><\/span><\/span><\/span>massa do el\u00e9tron \u00e9 9,1.10<\/b><\/span><\/span><\/span>-31<\/b><\/span><\/span><\/sup><\/span>kg<\/b><\/span><\/span><\/span>, a <\/b><\/span><\/span><\/span>velocidade da luz no v\u00e1cuo \u00e9 3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>m\/s e a constante de Planck \u00e9 6,6.10<\/b><\/span><\/span><\/span>-34<\/b><\/span><\/span><\/sup><\/span>J.s.<\/b><\/span><\/span><\/span><\/p>\n

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

\u00a0<\/span>a<\/span><\/span><\/span>)<\/b><\/span><\/span><\/span> <\/b>As <\/b><\/span><\/span><\/span>energias dos f\u00f3tons <\/b><\/span><\/span><\/span>que surgiram <\/b><\/span><\/span><\/span>foram obtidas atrav\u00e9s das massas do el\u00e9tron e do p\u00f3sitron<\/b><\/span><\/span><\/span>\"\"<\/p>\n

que <\/b><\/span><\/span><\/span>desapareceram no processo de aniquila\u00e7\u00e3o<\/b><\/span><\/span><\/span>.<\/b><\/span><\/span><\/span><\/p>\n

Essa <\/b><\/span><\/span><\/span>transforma\u00e7\u00e3o de massa em energia \u00e9 explicada <\/b><\/span><\/span><\/span>pela <\/b><\/span><\/span><\/span>teoria da relatividade de Einstein <\/b><\/span><\/span><\/span>na equa\u00e7\u00e3o <\/b><\/span><\/span><\/span>E = mc<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>, onde m \u00e9 a quantidade de massas convertidas em energia e c a velocidade da luz no v\u00e1cuo, de valor c = 3,0.10<\/b><\/span><\/span><\/span>8 <\/b><\/span><\/span><\/sup><\/span>ms.<\/b><\/span><\/span><\/span><\/p>\n

b)<\/b><\/span><\/span><\/span> <\/b>A <\/b><\/span><\/span><\/span>energia de um f\u00f3ton (E) e a sua frequ\u00eancia (f) <\/b><\/span><\/span><\/span>est\u00e3o <\/b><\/span><\/span><\/span>relacionadas pela express\u00e3o E = h . f<\/b><\/span><\/span><\/span>, em que <\/b><\/span><\/span><\/span>h \u00e9 a constante de Planck.<\/b><\/span><\/span><\/span><\/p>\n

Igualando as energias<\/b><\/span><\/span><\/span> dos <\/b><\/span><\/span><\/span>dois f\u00f3tons ao equivalente em energia das massas das part\u00edculas aniquiladas (el\u00e9tron e p\u00f3sitron)\u00a0 \"\"\u00a0\u00a0E<\/b><\/span><\/span><\/span>f\u00f3tons<\/b><\/span><\/span><\/sub><\/span>\u00a0= E<\/b><\/span><\/span><\/span>massas equivalentes<\/b><\/span><\/span><\/sub><\/span>\u00a0 \"\"\u00a0 \u00a02.(h.f) = 2.M<\/b><\/span><\/span><\/span>el\u00e9tron<\/b><\/span><\/span><\/sub><\/span>\u00a0.c<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0\u00a0\"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span><\/p>\n

6,6.10<\/b><\/span><\/span><\/span>-34<\/b><\/span><\/span><\/sup><\/span>.f = 9,1.10<\/b><\/span><\/span><\/span>-31<\/b><\/span><\/span><\/sup><\/span>.(3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>f = 1,2.10<\/b><\/span><\/span><\/span>20 <\/b><\/span><\/span><\/sup><\/span>Hz.<\/b><\/span><\/span><\/span><\/p>\n

03-(UFPE-PE)<\/b><\/span><\/span><\/span> <\/b><\/p>\n

\"\"<\/p>\n

O <\/b><\/span><\/span><\/span>c\u00e9sio met\u00e1lico <\/b><\/span><\/span><\/span>tem uma <\/b><\/span><\/span><\/span>fun\u00e7\u00e3o trabalho (potencial de superf\u00edcie) de 1,8 eV.<\/b><\/span><\/span><\/span><\/p>\n

Qual<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>energia cin\u00e9tica m\u00e1xima dos el\u00e9trons, em eV<\/b><\/span><\/span><\/span>, que <\/b><\/span><\/span><\/span>escapam da superf\u00edcie do metal quando ele \u00e9 iluminado com luz ultravioleta<\/b><\/span><\/span><\/span> de <\/b><\/span><\/span><\/span>comprimento de onda igual a 327 nm? Considere: 1eV=1,6.10<\/b><\/span><\/span><\/span>-19<\/b><\/span><\/span><\/sup><\/span>J; h=6,63.10<\/b><\/span><\/span><\/span>-34<\/b><\/span><\/span><\/sup><\/span>J.s e C=3,0.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>m\/s<\/b><\/span><\/span><\/span><\/p>\n

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

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

E<\/b><\/span><\/span><\/span>cin.m\u00e1x .<\/b><\/span><\/span><\/sub><\/span>= h.f \u2013 W\u00a0 \"\"<\/b><\/span><\/span><\/span> \u00a0 V = c = <\/b><\/span><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span><\/span>f \u00a0\"\"\u00a0 <\/b><\/span><\/span><\/span>f = C\/\u03bb\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 E<\/b><\/span><\/span><\/span>cin.m\u00e1x .<\/b><\/span><\/span><\/sub><\/span>= h.(C\/\u03bb) – W \"\" W = 6,63.10<\/b><\/span><\/span><\/span>34<\/b><\/span><\/span><\/sup><\/span>.(3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>\/327. 10<\/b><\/span><\/span><\/span>-9<\/b><\/span><\/span><\/sup><\/span>)\u00a0\u2013 1,8.1,6.10<\/b><\/span><\/span><\/span>-19<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"\u00a0 E<\/b><\/span><\/span><\/span>cin.m\u00e1x.<\/b><\/span><\/span><\/sub><\/span>=3,8 \u2013 1,8\u00a0 \"\" \u00a0<\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>cin.m\u00e1x.<\/b><\/span><\/span><\/sub><\/span>=2,0 eV.<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

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

a)<\/b><\/span><\/span><\/span> Dados:\u00a0m<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0= m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0= 2 g = 2.10<\/b><\/span><\/span><\/span>-3<\/b><\/span><\/span><\/sup><\/span>\u00a0kg; c = 3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>\u00a0m\/s\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 a <\/b><\/span><\/span><\/span>massa<\/b><\/span><\/span><\/span> a ser <\/b><\/span><\/span><\/span>convertida em energia \u00e9 m = m<\/b><\/span><\/span><\/span>1<\/b><\/span><\/span><\/sub><\/span>\u00a0+ m<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sub><\/span>\u00a0= 4.10<\/b><\/span><\/span><\/span>-3<\/b><\/span><\/span><\/sup><\/span>\u00a0kg \u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0\u00a0 da <\/b><\/span><\/span><\/span>equa\u00e7\u00e3o de Einstein, <\/b><\/span><\/span><\/span>a <\/b><\/span><\/span><\/span>energia liberada na aniquila\u00e7\u00e3o \u00e9\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 <\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>lib<\/b><\/span><\/span><\/sub><\/span>\u00a0= mc<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0<\/b><\/span><\/span><\/span> \"\"\u00a0 E<\/b><\/span><\/span><\/span>lib<\/b><\/span><\/span><\/sub><\/span>\u00a0= 4.10<\/b><\/span><\/span><\/span>-3<\/b><\/span><\/span><\/sup><\/span>.(3.10<\/b><\/span><\/span><\/span>8<\/b><\/span><\/span><\/sup><\/span>)<\/b><\/span><\/span><\/span>2<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"\u00a0 E<\/b><\/span><\/span><\/span>lib<\/b><\/span><\/span><\/sub><\/span>\u00a0= 4.10<\/b><\/span><\/span><\/span>-3<\/b><\/span><\/span><\/sup><\/span>.9.10<\/b><\/span><\/span><\/span>16<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"\u00a0<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>E<\/b><\/span><\/span><\/span>lib <\/b><\/span><\/span><\/sub><\/span>= 3,6.10<\/b><\/span><\/span><\/span>14<\/b><\/span><\/span><\/sup><\/span>\u00a0J.<\/b><\/span><\/span><\/span><\/p>\n

b)<\/b><\/span><\/span><\/span> Dados<\/b><\/span><\/span><\/span>\u00a0 \"\"\u00a0\u00a0 popula\u00e7\u00e3o\u00a0de 1 milh\u00e3o de habitantes\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>N = 10<\/b><\/span><\/span><\/span>6<\/b><\/span><\/span><\/sup><\/span>\u00a0habitantes\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 consumo m\u00e9dio \"\"\u00a0<\/b><\/span><\/span><\/span>100 kWh\/habitante.m\u00eas. <\/b><\/span><\/span><\/span> \u00a0<\/b><\/span><\/span><\/span><\/p>\n

Lembrando que <\/b><\/span><\/span><\/span>1 kWh = 3,6.10<\/b><\/span><\/span><\/span>6<\/b><\/span><\/span><\/sup><\/span>\u00a0J,<\/b><\/span><\/span><\/span> a <\/b><\/span><\/span><\/span>pot\u00eancia consumida mensalmente pela cidade \u00e9\u00a0 <\/b><\/span><\/span><\/span>\u00a0\"\" \u00a0<\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>otcons<\/b><\/span><\/span><\/sub><\/span>\u00a0= <\/b><\/span><\/span><\/span>100.10<\/b><\/span><\/span><\/span>6<\/b><\/span><\/span><\/sup><\/span>.3,6.10<\/b><\/span><\/span><\/span>6<\/b><\/span><\/span><\/sup><\/span>\u00a0<\/b><\/span><\/span><\/span>= 360.10<\/b><\/span><\/span><\/span>12<\/b><\/span><\/span><\/sup><\/span>\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 P<\/b><\/span><\/span><\/span>otcons<\/b><\/span><\/span><\/sub><\/span>=3,6.10<\/b><\/span><\/span><\/span>14<\/b><\/span><\/span><\/sup><\/span>\u00a0J\/m\u00eas\u00a0 \"\"\u00a0 <\/b><\/span><\/span><\/span>P<\/b><\/span><\/span><\/span>otcons <\/b><\/span><\/span><\/sub><\/span>= E<\/b><\/span><\/span><\/span>lib<\/b><\/span><\/span><\/sub><\/span>\/\u0394t\u00a0 \"\"<\/b><\/span><\/span><\/span>\u00a0 3,6.10<\/b><\/span><\/span><\/span>14 <\/b><\/span><\/span><\/sup><\/span>= 3,6.10<\/b><\/span><\/span><\/span>14<\/b><\/span><\/span><\/sup><\/span>\/\u0394t \u00a0 \u00a0\u00a0<\/b><\/span><\/span><\/span><\/p>\n

\"\" \u0394t = 1 m\u00eas.<\/b><\/span><\/span><\/span><\/p>\n

 <\/p>\n

Confira os exerc\u00edcios com resolu\u00e7\u00f5es comentadas<\/span><\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"

Efeito Fotoel\u00e9trico Introdu\u00e7\u00e3o \u00e0 F\u00edsica Moderna A F\u00edsica cl\u00e1ssica, das leis que regem os a Cinem\u00e1tica, a Din\u00e2mica, a \u00d3ptica, a Ondulat\u00f3ria, o Eletromagnetismo, etc. que explicam o funcionamento dos nossos aparelhos el\u00e9tricos e eletr\u00f4nicos, dos carros, trens, \u00a0e que s\u00e3o partes importantes e relevantes da F\u00edsica, continua sendo v\u00e1lida, precisa, \u00a0e at\u00e9 sendo aperfei\u00e7oada. No entanto, s\u00f3 \u00e9 aplic\u00e1vel<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":125,"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-2478","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2478","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=2478"}],"version-history":[{"count":2,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2478\/revisions"}],"predecessor-version":[{"id":2486,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2478\/revisions\/2486"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/125"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2478"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}