{"id":2203,"date":"2016-05-14T23:33:06","date_gmt":"2016-05-14T23:33:06","guid":{"rendered":"http:\/\/fisicaevestibular.com.br\/novo\/?page_id=2203"},"modified":"2024-09-02T14:34:39","modified_gmt":"2024-09-02T14:34:39","slug":"reflexao-total-resolucao","status":"publish","type":"page","link":"https:\/\/fisicaevestibular.com.br\/novo\/optica\/optica-geometrica\/reflexao-total\/reflexao-total-resolucao\/","title":{"rendered":"Reflex\u00e3o Total – Resolu\u00e7\u00e3o"},"content":{"rendered":"

Resolu\u00e7\u00e3o comentada dos exerc\u00edcios de vestibulares sobre <\/b><\/span><\/span><\/span><\/p>\n

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

 <\/p>\n

 <\/p>\n

01-<\/b><\/span><\/span><\/span> <\/b>Se ele incide com \u00e2ngulo limite (\u03b8=L), ele emerge rasante\u00a0\u00a0<\/b><\/span><\/span>R- A<\/b><\/span><\/span><\/p>\n

02-<\/b><\/span><\/span><\/span> <\/b>R- E<\/b><\/span><\/span><\/p>\n

03-<\/b><\/span><\/span><\/span> <\/b>R- C\u00a0 —\u00a0 nos outros casos estaria passando de um meio de menor \u00edndice para um meio de maior \u00edndice e haveria refra\u00e7\u00e3o.<\/b><\/span><\/span><\/p>\n

04-<\/b><\/span><\/span><\/span> <\/b>(01) Falsa \u2013 \u00e9 baseado na lei de Snell-Descartes<\/b><\/span><\/span><\/p>\n

(02) Falsa \u2013 Depende do \u00e2ngulo de incid\u00eancia que deve ser maior que o \u00e2ngulo limita<\/b><\/span><\/span><\/p>\n

(04) Falsa \u2013 quem n\u00e3o varia \u00e9 a frequ\u00eancia<\/b><\/span><\/span><\/p>\n

(08) Verdadeira \u2013 (veja teoria)<\/b><\/span><\/span><\/p>\n

05-<\/b><\/span><\/span><\/span> <\/b>senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 senL=1\/2\u00a0 —\u00a0 L=30<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 sofrer\u00e1 refra\u00e7\u00e3o se incidir com \u00e2ngulo inferior ao \u00e2ngulo limite\u00a0\u00a0<\/b><\/span><\/span>R- C<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span><\/p>\n

06-<\/b><\/span><\/span><\/span> <\/b>R- A\u00a0 (veja teoria)<\/b><\/span><\/span><\/p>\n

07-<\/b><\/span><\/span><\/span> <\/b>senL(\u03b1)=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>=n(ar)\/n(t)\u00a0 —\u00a0\u00a0 senL(\u03b1)=n(ar)\/n(ar).(1 + e<\/b><\/span><\/span>-bt<\/b><\/span><\/span><\/sup>)\u00a0 —\u00a0 senL(\u03b1)=(1 + e<\/b><\/span><\/span>-bt<\/b><\/span><\/span><\/sup>)\u00a0 —\u00a0\u00a0 observe nessa express\u00e3o que \u00e0 medida que n(t) aumenta senL(\u03b1) tamb\u00e9m aumenta, at\u00e9 que L chegue a 90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>,\u00a0 e senL(\u03b1)=1, quando a luz emerge rasante\u00a0\u00a0<\/b><\/span><\/span>R- B<\/b><\/span><\/span><\/p>\n

08-<\/b><\/span><\/span><\/span> <\/b>Observe na sequ\u00eancia de figuras abaixo que \u00e0 medida que i diminui no sentido anti-hor\u00e1rio, r tamb\u00e9m diminui, mas no sentido<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

hor\u00e1rio\u00a0\u00a0<\/b><\/span><\/span>R- E<\/b><\/span><\/span><\/p>\n

09-<\/b><\/span><\/span><\/span> <\/b>a) Vidro e l\u00edquido possuem o mesmo \u00edndice de refra\u00e7\u00e3o, (n=1,5), pois a luz n\u00e3o sofre desvio\u00a0 ao passar de um para o outro\u00a0<\/b><\/span><\/span>\u2013 R- 1,5<\/b><\/span><\/span><\/p>\n

b) Refra\u00e7\u00e3o do ar para o vidro<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

b) n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>=C\/V<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 1,5=3.10<\/b><\/span><\/span>8<\/b><\/span><\/span><\/sup>\/V<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>V<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>=2.10<\/b><\/span><\/span>8<\/b><\/span><\/span><\/sup>m\/s<\/b><\/span><\/span><\/p>\n

c)n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.seni=n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.senr\u00a0 —\u00a0 1.1\/2=1,5.senr\u00a0 —\u00a0 senr=1\/3\u00a0 —\u00a0 r=19,5<\/b><\/span><\/span>o\u00a0<\/b><\/span><\/span><\/sup>\u00a0—\u00a0 no ponto C (interface l\u00edquido)-ar)\u00a0 —\u00a0 senl=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>\u00a0<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0senL=1\/1,5\u00a0 —\u00a0 senL=0,66 e sen70,5<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>=0,94\u00a0 —\u00a0 como senL<sen70,5<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 L<70,5<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 n\u00e3o haver\u00e1 refra\u00e7\u00e3o e sim reflex\u00e3o total, pois o \u00e2ngulo de incid\u00eancia \u00e9 maior que o \u00e2ngulo limite.<\/b><\/span><\/span><\/p>\n

10-<\/b><\/span><\/span><\/span> <\/b>R- B \u2013 Se incidir com \u00e2ngulo inferior ao \u00e2ngulo limite, haver\u00e1 refra\u00e7\u00e3o, mas acompanhada de reflex\u00e3o e se incidir com \u00e2ngulo superior ao \u00e2ngulo limite, haver\u00e1 somente reflex\u00e3o (total).<\/b><\/span><\/span><\/p>\n

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

12-<\/b><\/span><\/span><\/span> <\/b>A luz se propaga no interior do n\u00facleo da fibra \u00f3ptica num caminho totalmente espelhado devido ao fen\u00f4meno da\u00a0<\/b><\/span><\/span>reflex\u00e3o total<\/b><\/span><\/span>\u00a0que ocorrer\u00e1 no interior do n\u00facleo desde que o \u00edndice de refra\u00e7\u00e3o do n\u00facleo (n<\/b><\/span><\/span>n<\/b><\/span><\/span><\/sub>) seja maior que o \u00edndice de refra\u00e7\u00e3o da casca (n<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>) e que o \u00e2ngulo de incid\u00eancia em rela\u00e7\u00e3o \u00e0 normal ao incidir na casca seja maior que o\u00a0<\/b><\/span><\/span>\u00e2ngulo limite L.<\/b><\/span><\/span><\/p>\n

a)<\/b><\/span><\/span><\/p>\n

 <\/p>\n

\"\"<\/p>\n

b) n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen\u03b8=n<\/b><\/span><\/span>n<\/b><\/span><\/span><\/sub>.senr\u00a0 —\u00a0 1.0,75=1,5senr\u00a0 —\u00a0\u00a0 senr=1\/2\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>r=30<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/p>\n

c<\/b><\/span><\/span>) r + i\u2019 + 90=180<\/b><\/span><\/span>\u00a0 —\u00a0 i\u2019=60<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/p>\n

c)\u00a0\"\"<\/b><\/span><\/span><\/p>\n

d) na interface n\u00facleo-casca\u00a0 —\u00a0 n<\/b><\/span><\/span>n<\/b><\/span><\/span><\/sub>=1,5\u00a0 —\u00a0 n<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>=1,3\u00a0 —\u00a0 senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>=1,3\/1,5\u00a0 —\u00a0 senL=0,8666\u00a0 —\u00a0 seni\u2019=sen60<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>=0,88603\u00a0 —\u00a0 seni\u2019 > senL\u00a0\u00a0<\/b><\/span><\/span>— i\u2019>L \u2013 reflex\u00e3o total<\/b><\/span><\/span>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/b><\/span><\/span><\/p>\n

14-<\/b><\/span><\/span><\/span> <\/b>Observe na figura acima que o \u00e2ngulo de incid\u00eancia na interface 2-3 tamb\u00e9m \u00e9 r e que\u00a0 a incid\u00eancia \u00e9 rasante (90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>), de acordo com o enunciado\u00a0 —\u00a0 n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>.senr=n<\/b><\/span><\/span>3<\/b><\/span><\/span><\/sub>.sen90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 1,5.2.sen\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/sub>1,5=1.sen90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 sen \u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/sub>=12\u00a0\u00a0<\/b><\/span><\/span>—\u00a0 \u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/sub>=30<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup><\/p>\n

15-<\/b><\/span><\/span><\/span> <\/b>a) Reflex\u00e3o total dos raios que atingem a interface \u00e1gua-ar fora do disco de madeira e que n\u00e3o atingem os olhos do observador.<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

b) As l\u00e2mpadas 1 e 2, pois est\u00e3o mais pr\u00f3ximas do anteparo opaco e o \u00e2ngulo de incid\u00eancia na interface \u00e1gua-ar \u00e9 menor.<\/b><\/span><\/span><\/p>\n

c) Para que as tr\u00eas l\u00e2mpadas inferiores sejam vis\u00edveis, a regi\u00e3o iluminada deve estar abaixo da segunda l\u00e2mpada.. Assim,todos os raios de luz que saem da segunda l\u00e2mpada, a partir do ponto P, devem sofrer reflex\u00e3o total para n\u00e3o atingirem os olhos do observador.<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

Aplicando Pit\u00e1goras no tri\u00e2ngulo ret\u00e2ngulo da figura da direita\u00a0 —\u00a0 h<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>=(2L)<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0+ R<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 h<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>=4L<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0+ R<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 senL=R\/h\u00a0 —senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>n<\/b><\/span><\/span>maior=<\/b><\/span><\/span><\/sub>=n(ar)n(H)\u00a0 — R\/h=n(ar)\/n(H)\u00a0\u00a0<\/b><\/span><\/span>—\u00a0 R\/\u221a(4L<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0+ R<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>)=n(ar)\/n(H)<\/b><\/span><\/span><\/p>\n

16-<\/b><\/span><\/span><\/span> <\/b>Como o raio incide perpendicularmente na face A ele n\u00e3o sofre desvio at\u00e9 atingir a face B, onde <\/b><\/span><\/span><\/p>\n

0cCC<\/b><\/span><\/span><\/span>\"\"<\/p>\n

sen45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>=.\u221a2\/2=070\u00a0 —\u00a0\u00a0\u00a0\u00a0 o \u00e2ngulo limite na interface prisma-\u00e1gua vale senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 senL=1,33\/1,52\u00a0 —\u00a0 senL=0,87\u00a0 —\u00a0<\/b><\/span><\/span><\/p>\n

sen45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup><senL\u00a0 —\u00a0\u00a0 45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup><L\u00a0 —\u00a0 incide na face B com \u00e2ngulo inferior ao \u00e2ngulo limite, ou seja, n\u00e3o sofre reflex\u00e3o total em B, mas sim refra\u00e7\u00e3o, passando para a \u00e1gua<\/b><\/span><\/span>.\u00a0 R- A<\/b><\/span><\/span><\/p>\n

17-<\/b><\/span><\/span><\/span> <\/b>Aplicando\u00a0 Snell-Descartes na face superior\u00a0\u00ae\u00a0n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>=n.senr\u00a0\u00a0 —\u00a0 1.\u221a2\/2= n.senr\u00a0\u00a0 —\u00a0 senr= \u221a2\/2n<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

Para que haja reflex\u00e3o total no ponto P da face A, o \u00e2ngulo de incid\u00eancia i=(90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0\u2013 r) deve ser maior que o \u00e2ngulo limite L ou seja, sem(90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>-r) > senL\u00a0 —\u00a0\u00a0 Impor a condi\u00e7\u00e3o \u2013 sen (90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>– r)>\u00a0senL\u00a0\u00a0 —\u00a0 cosr > senL\u00a0 —\u00a0 \u221a(1 \u2013 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0r)\u00a0>\u00a0sen L\u00a0 —\u00a0 (1 \u2013 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0r)\u00a0>\u00a0sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0L\u00a0\u00a0\u00a0 —\u00a0\u00a0\u00a0 1-1\/2n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0\u00a0>\u00a01\/n<\/b><\/span><\/span>2\u00a0<\/b><\/span><\/span><\/sup>\u00a0\u00a0—\u00a0\u00a0 2n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0>\u00a03\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>n\u00a0>\u00a01,5\u00a0 R- C<\/b><\/span><\/span><\/p>\n

18-<\/b><\/span><\/span><\/span><\/span> <\/b>a) n<\/b><\/span><\/span><\/span>ar<\/b><\/span><\/span><\/span><\/sub>.sen<\/b><\/span><\/span><\/span>\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/span><\/sub>\u00a0= n.sen\u00a0<\/b><\/span><\/span><\/span>\u03b8<\/b><\/span><\/span>2<\/b><\/span><\/span><\/span><\/sub>\u00a0 —\u00a0 1.sen\u00a0<\/b><\/span><\/span><\/span>\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/span><\/sub>=\u221a2.sen30<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/span><\/sup>\u00a0 —\u00a0 sen\u00a0<\/b><\/span><\/span><\/span>\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/span><\/sub>=\u221a2\/2\u00a0 —\u00a0\u00a0<\/b><\/span><\/span><\/span>\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/span><\/sub>=45<\/b><\/span><\/span><\/span>o<\/b><\/span><\/span><\/span><\/sup><\/p>\n

b) Observe na figura abaixo que ele incide no ponto P com \u00e2ngulo i=60<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 \u00e2ngulo limite L na interface ar-fibra\u00a0 —\u00a0 senL=1\/\u221a2<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0 —\u00a0 senL=\u221a2\/2\u00a0 —\u00a0 L=45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 o \u00e2ngulo de incid\u00eancia i=60<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0\u00e9 maior que o \u00e2ngulo limite L=45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>, que \u00e9 condi\u00e7\u00e3o para que ele sofra reflex\u00e3o total.<\/b><\/span><\/span><\/p>\n

19-<\/b><\/span><\/span><\/span> <\/b>a) Para que a miragem seja vista, o \u00e2ngulo limite tem que ser maior que 84<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0<\/b><\/span><\/span><\/p>\n

senL=n2(menor)\/n1(maior) \u00a0— \u00a00,995=n2\/1,010 \u00a0— \u00a0n2=1,005<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

 <\/p>\n

b) Quanto menos refringente \u00e9 o meio,\u00a0<\/b><\/span><\/span>menor \u00e9 seu \u00edndice de refra\u00e7\u00e3o (n) e maior ser\u00e1 sua velocidade V (meio 2)<\/b><\/span><\/span><\/p>\n

20-<\/b><\/span><\/span><\/span> <\/b>R- B (veja teoria)<\/b><\/span><\/span><\/p>\n

21-<\/b><\/span><\/span><\/span> <\/b>Aplicando Snell-Descartes na 1<\/b><\/span><\/span>a<\/b><\/span><\/span><\/sup>\u00a0face\u00a0 —\u00a0 n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen\u03b8=n<\/b><\/span><\/span>n\u00facleo<\/b><\/span><\/span><\/sub>.senr\u00a0 —1.sen\u03b8\u00a0 —\u00a0 1.sen\u03b8=1,6.senr\u00a0 —\u00a0 senr=sen\u03b8\/1,6\u00a0\u00a0<\/b><\/span><\/span>I<\/b><\/span><\/span>\u00a0\u00a0<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

\u00a0Para haver reflex\u00e3o total na interface n\u00facleo-revestimento, o \u00e2ngulo de incid\u00eancia i=(90 \u2013 r) tem que ser maior que o \u00e2ngulo limite L\u00a0\u00ae\u00a0 (90-r)>L\u00a0\u00ae\u00a0sen (90-r)>senL\u00a0\u00ae\u00a0cosr>0,95\u00a0\u00a0 II<\/b><\/span><\/span><\/p>\n

Aplicar \u2013 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r + cos<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0r = 1\u00a0 —\u00a0 cosr=\u221a(1-sem<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0r)\u00a0 III<\/b><\/span><\/span><\/p>\n

III em II\u00a0 —\u00a0 \u221a(1 \u2013 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r) > 0,95\u00a0 —\u00a0 (\u221a1 \u2013 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r)<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0> (0,95)<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0 — 1 – sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r > 0,902\u00a0 —\u00a0 senr>0,31\u00a0<\/b><\/span><\/span>\u00a0IV\u00a0\u00a0<\/b><\/span><\/span>—\u00a0 IV em I\u00a0 —\u00a0 sen\u03b8\/1,6>0,31\u00a0 —\u00a0 sen\u03b8>0,5\u00a0\u00a0<\/b><\/span><\/span>—\u00a0 \u03b8>30<\/b><\/span><\/span>0<\/b><\/span><\/span><\/sup>\u00a0(condi\u00e7\u00e3o para que a luz sofra reflex\u00f5es totais no interior da fibra \u00f3ptica)<\/b><\/span><\/span><\/p>\n

22-<\/b><\/span><\/span><\/span> <\/b>R- C (veja teoria)<\/b><\/span><\/span><\/p>\n

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

Observe na figura ao lado que os dois raios de luz incidem com \u00e2ngulo de 45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0 o \u00e2ngulo limite para o raio azul (a) \u00e9 de 44<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>e, como ele incide com 45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0que \u00e9\u00a0 superior ao \u00e2ngulo limite, ele sofre reflex\u00e3o total, retornando ao prisma. O raio vermelho (v) incide tamb\u00e9m com 45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>, que \u00e9 inferior ao seu \u00e2ngulo limite (46<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>), sofrendo refra\u00e7\u00e3o e passando para o ar<\/b><\/span><\/span>.\u00a0 R- E<\/b><\/span><\/span><\/p>\n

24-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>As ondas eletromagn\u00e9ticas emitidas na regi\u00e3o litor\u00e2nea do Brasil atingem a regi\u00e3o amaz\u00f4nica ap\u00f3s sofrer reflex\u00e3o total na ionosfera.<\/b><\/span><\/span><\/p>\n

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

25-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>I) Correta\u00a0 —\u00a0 como a atmosfera \u00e9 transparente, mas n\u00e3o homog\u00eanea, os raios solares sofrem desvio ao atravess\u00e1-la, fazendo com que o p\u00f4r do sol seja uma miragem\u00a0 —\u00a0 como, na refra\u00e7\u00e3o, as radia\u00e7\u00f5es de menor frequ\u00eancia (vermelha, amarela e alaranjada) sofrem menor desvio, o observador v\u00ea a imagem do Sol com predomin\u00e2ncia dessas cores, da\u00ed, aquele tom roseado\u00a0 —\u00a0\u00a0 como mostra a figura ilustra (de maneira exagerada).<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

(II) Falsa\u00a0 —\u00a0 o ar \u00e9 menos refringente que a \u00e1gua\u00a0 —\u00a0 ao passar do meio menos para o mais refringente, a luz aproxima da normal, n\u00e3o ocorrendo reflex\u00e3o total\u00a0 —\u00a0 esse fen\u00f4meno s\u00f3 ocorre quando o sentido de propaga\u00e7\u00e3o da luz \u00e9 do meio mais para o menos refringente, quando o \u00e2ngulo de incid\u00eancia \u00e9 maior que o \u00e2ngulo limite.<\/b><\/span><\/span><\/p>\n

(III) Falsa\u00a0 —\u00a0 na refra\u00e7\u00e3o n\u00e3o h\u00e1 altera\u00e7\u00e3o da frequ\u00eancia.\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span><\/p>\n

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

26-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>A frequ\u00eancia \u00e9 caracter\u00edstica da luz, \u00e9 a mesma para qualquer meio desde que a radia\u00e7\u00e3o (cor) seja a mesma\u00a0 —\u00a0 assim, ao mudar de meio, a frequ\u00eancia do feixe n\u00e3o se altera\u00a0 —\u00a0 o comprimento de onda pode ser obtido a partir da lei de Snell\u00a0 —\u00a0 seni\/senr=n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>=V<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/V<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>=\u03bb<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/ \u03bb<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>= \u03bb<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/ \u03bb<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 se n<\/b><\/span><\/span>\u00e1gua\u00a0<\/b><\/span><\/span><\/sub>> n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 \u03bb<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\u00a0> \u03bb<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0R- E<\/b><\/span><\/span><\/p>\n

27-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>a) Para um material convencional, o raio incidente e o raio refletido est\u00e3o no mesmo meio, em quadrantes adjacentes; o raio incidente e o refratado est\u00e3o em meios diferentes, em quadrantes opostos\u00a0 —\u00a0 assim, para um metamaterial, a trajet\u00f3ria \u00e9 a do<\/b><\/span><\/span><\/p>\n

raio E<\/b><\/span><\/span>\u00a0 —\u00a0 \u2502n<\/b><\/span><\/span>1<\/b><\/span><\/span><\/sub>\u2502.sen\u03b8<\/b><\/span><\/span>1<\/b><\/span><\/span><\/sub>\u00a0= \u2502n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u2502.sen\u03b8<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 1,8×0,5=\u2502n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u2502x \u221a2\/2\u00a0 —\u00a0 \u2502n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u2502= 1,8\/1,4\u00a0 —\u00a0<\/b><\/span><\/span>\u2502n<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u2502=1,29<\/b><\/span><\/span><\/p>\n

b) Substituindo os valores fornecidos para \u03b5 e para \u03bc\u00a0 na express\u00e3o fornecida\u00a0 —\u00a0 v=1\/\u221a(2.10<\/b><\/span><\/span>-11<\/b><\/span><\/span><\/sup>\u00a0x 1,25.10<\/b><\/span><\/span>-6<\/b><\/span><\/span><\/sup>)\u00a0 —\u00a0 v=2,0.10<\/b><\/span><\/span>-8<\/b><\/span><\/span><\/sup>m\/s\u00a0 —\u00a0<\/b><\/span><\/span><\/p>\n

n=c\/v=3.10<\/b><\/span><\/span>8<\/b><\/span><\/span><\/sup>\/2.10<\/b><\/span><\/span>8<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0n=1,5<\/b><\/span><\/span><\/p>\n

28-<\/b><\/span><\/span><\/span><\/p>\n

\"\"<\/p>\n

29-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>1. Verdadeira\u00a0 —\u00a0 dispers\u00e3o \u00e9 o fen\u00f4meno que ocorre quando um feixe de luz policrom\u00e1tica sofre refra\u00e7\u00e3o, com separa\u00e7\u00e3o das cores componentes.<\/b><\/span><\/span><\/p>\n

2. Verdadeira\u00a0 —\u00a0 o \u00e2ngulo de incid\u00eancia \u00e9 igual ao de reflex\u00e3o (2\u00aa lei da reflex\u00e3o).<\/b><\/span><\/span><\/p>\n

3. Falsa\u00a0 —\u00a0 a radia\u00e7\u00e3o violeta \u00e9 que apresenta maior desvio.\u00a0<\/b><\/span><\/span><\/p>\n

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

30-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Observe o esquema abaixo\u00a0 —\u00a0 voc\u00ea deve calcular o \u00edndice de refra\u00e7\u00e3o do prisma que provoque emerg\u00eancia rasante o que<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

ocorre quando r=90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0quando o \u00e2ngulo de incid\u00eancia \u00e9 i=30<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0na face B\u00a0 —\u00a0 pela Lei de Snell\u00a0 —\u00a0 n<\/b><\/span><\/span>P\u00a0<\/b><\/span><\/span><\/sub>sen30\u00b0 = n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>sen90\u00b0\u00a0 — \u00a0N<\/b><\/span><\/span>P<\/b><\/span><\/span><\/sub>.0,5=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.1\u00a0 —\u00a0 \u00a0n<\/b><\/span><\/span>P<\/b><\/span><\/span><\/sub>\/2=1\u00a0 —\u00a0 n<\/b><\/span><\/span>P<\/b><\/span><\/span><\/sub>=2\u00a0 —\u00a0 para que ocorra reflex\u00e3o total\u00a0 —\u00a0n<\/b><\/span><\/span>p<\/b><\/span><\/span><\/sub>\/2 = 1\u00a0n\u00ad<\/b><\/span><\/span>p<\/b><\/span><\/span><\/sub>\u00a0= 2\u00a0 —\u00a0 \u00a0<\/b><\/span><\/span>n<\/b><\/span><\/span>p<\/b><\/span><\/span><\/sub>\u00a0> 2\u00a0<\/b><\/span><\/span><\/p>\n

31-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Dado\u00a0 —\u00a0\u00a0 n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\u00a0= 1\u00a0 —\u00a0 n = 3\/2\u00a0 —\u00a0 para que toda a luz incidente na superf\u00edcie P sofre emerg\u00eancia pela superf\u00edcie Q \u00e9 necess\u00e1rio que todos os raios do feixe sofram reflex\u00e3o total ao incidir na superf\u00edcie c\u00f4ncava de maior raio\u00a0 —\u00a0 a figura mostra dois raios lim\u00edtrofes, a e b, do feixe\u00a0 —\u00a0 para que ocorra reflex\u00e3o total, o \u00e2ngulo de incid\u00eancia (i) deve ser maior que o \u00e2ngulo limite (L)\u00a0 —\u00a0\u00a0 assim, se o raio que incide com menor \u00e2ngulo (raio a) sofrer reflex\u00e3o total, o feixe inteiro tamb\u00e9m sofrer\u00e1 reflex\u00e3o total\u00a0 —\u00a0 I<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u00a0> L\u00a0 —\u00a0 seni<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>\u00a0> sem L (I)\u00a0 —\u00a0 o seno do \u00e2ngulo limite entre dois meios \u00e9 dado pela raz\u00e3o entre o \u00edndice do meio (\u2013) refringente e o do (+) refringente\u00a0 —\u00a0 sem L=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/n=1\/(3\/2)\u00a0 —\u00a0 sem L=2\/3 (II)\u00a0 —\u00a0 observe o tri\u00e2ngulo ret\u00e2ngulo mostrado na figura\u00a0 —\u00a0<\/b><\/span><\/span>\"\"<\/p>\n

Seni<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sub>=R\/(R + d) (III)\u00a0 —\u00a0 substituindo (II) e (III) em (I)\u00a0 —\u00a0 R\/(R + d) > 2\/3\u00a0 —\u00a0 3R > 2R + 2d\u00a0 —\u00a0 R > 2d\u00a0 —\u00a0 R\/d > 2\u00a0 —\u00a0<\/b><\/span><\/span><\/p>\n

(R\/d)<\/b><\/span><\/span>m\u00ednimo<\/b><\/span><\/span><\/sub>\u00a0 \u2248 2<\/b><\/span><\/span><\/p>\n

32-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Observe a figura abaixo\u00a0 —\u00a0 o asfalto se aquece, aquecendo as camadas de ar pr\u00f3ximas a ele\u00a0 —\u00a0 quanto mais baixa a camada, maior a sua temperatura\u00a0 —\u00a0 assim, a temperatura do ar diminui com a altura da camada\u00a0 —\u00a0 o ar quente sobe, fazendo com que as, camadas mais baixas se tornem mais rarefeitas provocando um aumento da densidade com a altura da camada\u00a0 — consequentemente, o \u00edndice de refra\u00e7\u00e3o tamb\u00e9m sofre um aumento, sendo as camadas inferiores menos refringentes\u00a0 —\u00a0 a passagem de um raio de uma camada (+) refringente para outra (\u2013) refringente faz com que o raio se afaste da normal na trajet\u00f3ria descendente, fazendo aumentar o \u00e2ngulo de refra\u00e7\u00e3o, at\u00e9 atingir o \u00e2ngulo limite e a reflex\u00e3o total, acontecendo o invers\u00e3o na trajet\u00f3ria ascendente.\u00a0\u00a0<\/b><\/span><\/span>\"\"<\/p>\n

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

33-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>a) V=C=\u03bbf\u00a0 —\u00a0 f=3.10<\/b><\/span><\/span>8<\/b><\/span><\/span><\/sup>\/500.10<\/b><\/span><\/span>-9<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>f=6,0.10<\/b><\/span><\/span>14<\/b><\/span><\/span><\/sup>Hz<\/b><\/span><\/span><\/p>\n

b)\u00a0<\/b><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>=<\/b><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span>\/n<\/b><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>=500.10<\/b><\/span><\/span>-9<\/b><\/span><\/span><\/sup>\/2\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0<\/b><\/span><\/span>\u03bb<\/b><\/span><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>=250 nm<\/b><\/span><\/span><\/p>\n

c) A condi\u00e7\u00e3o para que ocorra reflex\u00e3o total \u00e9 que o \u00e2ngulo de incid\u00eancia i deve ser maior que o \u00e2ngulo limite de incid\u00eancia que<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

deve ser igual ao \u00e2ngulo limite de refra\u00e7\u00e3o L\u00a0 —\u00a0 senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>=n<\/b><\/span><\/span>l\u00edquido<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>=1\/2\u00a0 —\u00a0 observe na figura que i=\u03b8 ou seja, \u03b8=L\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0sen\u03b8<\/b><\/span><\/span>m\u00ednimo<\/b><\/span><\/span><\/sub>=senL<\/b><\/span><\/span><\/p>\n

d) A condi\u00e7\u00e3o para que n\u00e3o ocorra reflex\u00e3o total \u00e9 que o \u00e2ngulo de incid\u00eancia i deve ser menor ou igual ao \u00e2ngulo limite de<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

incid\u00eancia\u00a0 —\u00a0 i \u2264 L\u00a0 —\u00a0 observando a figura\u00a0 — se\u00a0 i = \u03b8, ent\u00e3o \u03b8 \u2264 L\u00a0 —\u00a0 sen\u03b8=sen45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0\u2264 senL\u00a0 —\u00a0 \u221a2\/2 \u2264 n<\/b><\/span><\/span>l\u00edquido<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0<\/b><\/span><\/span><\/p>\n

n<\/b><\/span><\/span>l\u00edquido\u00a0\u00a0<\/b><\/span><\/span><\/sub>\u2265 \u221a2\/2.n<\/b><\/span><\/span>cristal<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0n<\/b><\/span><\/span>m\u00ednimo<\/b><\/span><\/span><\/sub>=\u221a2<\/b><\/span><\/span><\/p>\n

34-<\/b><\/span><\/span><\/span> <\/b>R- E\u00a0\u00a0<\/b><\/span><\/span>—\u00a0 veja teoria<\/b><\/span><\/span><\/p>\n

35-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>I. Correta\u00a0 —\u00a0 observe a figura abaixo\u00a0 —\u00a0 \u00e0 medida que os raios de luz provenientes do Sol penetram na atmosfera da Terra,v\u00e3o encontrando camadas de ar cada vez mais densas, mais refringentes e de maiores \u00edndices de refra\u00e7\u00e3o e aproximam-se cada vez mais da normal sofrendo os desvios mostrados\u00a0 —\u00a0 esses desvios fazem com que a imagem que se observa do Sol ao amanhecer e ao anoitecer\u00a0 encontra-se acima de sua real posi\u00e7\u00e3o, tomando-se como refer\u00eancia o horizonte.<\/b><\/span><\/span>\"\"<\/p>\n

II. Falsa\u00a0 —\u00a0 \u00e9 exatamente o contr\u00e1rio.<\/b><\/span><\/span><\/p>\n

III. Correta\u00a0 —\u00a0 o raio de luz se refrata sempre que passa de um meio menos refringente para outro mais refringente e, nesse caso se aproxima da normal.<\/b><\/span><\/span><\/p>\n

IV. Falsa\u00a0 —\u00a0 toda imagem virtual (obtida pelo prolongamento dos raios de luz) \u00e9 direita.<\/b><\/span><\/span><\/p>\n

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

36-<\/b><\/span><\/span><\/span>\u00a0<\/b><\/span><\/span><\/span>Observe a figura abaixo\u00a0 —\u00a0 dados\u00a0 —\u00a0\u00a0 n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\u00a0= 1 —\u00a0\u00a0 n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0=3\/2\u00a0 —\u00a0 \u00a0R = 10 cm\u00a0 —\u00a0 b = 0,5 cm\u00a0 —\u00a0 lei de Snell na refra\u00e7\u00e3o do ar para o vidro —\u00a0 n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.seni=n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.senr\u00a0 —\u00a0 como i e r s\u00e3o \u00e2ngulos muito pequenos, ent\u00e3o, de acordo com o<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

enunciado, voc\u00ea pode escrever\u00a0 —\u00a0 (n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>).(A\/R) = (n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>).(d\/2)\/R\u00a0 —\u00a0 1×0,5=3\/2xd\/2\u00a0 —\u00a0 d=2\/3 cm\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0R- B<\/b><\/span><\/span><\/p>\n

 <\/p>\n

37- Aplicando Snell-Descartes na 1<\/b><\/span><\/span>a<\/b><\/span><\/span><\/sup>\u00a0face\u00a0 —\u00a0 n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen\u03b8=n<\/b><\/span><\/span>n\u00facleo<\/b><\/span><\/span><\/sub>.senr\u00a0 —1.sen\u03b8\u00a0 —\u00a0 1.sen\u03b8=\u221a(3\/2).senr\u00a0 —<\/b><\/span><\/span><\/p>\n

\"\"<\/p>\n

sen\u03b8=\u221a3\u221a2.senr (I) — observe na figura que, para haver reflex\u00e3o total em P, o \u00e2ngulo (90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0\u2013 r) tem que ser o \u00e2ngulo limite L\u00a0 —\u00a0 senL=sen(90<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0\u2013 r)=cosr=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>=1\/\u221a(3\/2)\u00a0 —\u00a0 cosr=\u221a2\/\u221a3\u00a0 —\u00a0 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r + cos<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r = 1\u00a0 —\u00a0 sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r + (\u221a2\/\u221a3)<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>\u00a0= 1\u00a0 —<\/b><\/span><\/span><\/p>\n

sen<\/b><\/span><\/span>2<\/b><\/span><\/span><\/sup>r + 2\/3 = 1\u00a0 —\u00a0 senr=\u221a(1\/3)\u00a0 —\u00a0 senr=\u221a3\/3 (III)\u00a0 —\u00a0 (III) em (I)\u00a0 —\u00a0 sen\u03b8 = (\u221a3\/\u221a2). \u221a3\/3\u00a0 —\u00a0 sen\u03b8=3\/3.\u221a2\u00a0 —\u00a0 sen\u03b8=1\/\u221a2\u00a0 —\u00a0 sen\u03b8=\u221a2\/2\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0\u03b8=45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>.<\/b><\/span><\/span><\/p>\n

38-<\/b><\/span><\/span><\/span> <\/b>Dados: sen 48,6<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0= 0,75, cos 48,6\u00ba = 0,66.<\/b><\/span><\/span><\/p>\n

a) Observe na figura 1, nos dois tri\u00e2ngulos hachurados), que o \u00e2ngulo de incid\u00eancia da luz na superf\u00edcie de separa\u00e7\u00e3o \u00e1gua-<\/b><\/span><\/span><\/p>\n

vidro vale \u03b8\u00a0 — observe na figura 2 que o \u00e2ngulo de refra\u00e7\u00e3o na interface \u00e1gua-vidro \u00e9 \u03c6 e na interface vidro-ar, o \u00e2ngulo de incid\u00eancia \u00e9 \u03c6 e o de refra\u00e7\u00e3o \u00e9 \u03b2\u00a0 —\u00a0 lei de Snell-Descartes na interface \u00e1gua-vidro\u00a0 —\u00a0 n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>.sen\u03b8 = n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.sen\u03c6\u00a0\u00a0 —\u00a0 lei de Snell-Descartes na interface vidro-ar\u00a0 —n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.sen\u03c6 = n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen\u03b2\u00a0 —\u00a0 n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.sen\u03c6 = 1.sen\u03b2\u00a0\u00a0 —\u00a0 \u00e2ngulo limite (L) para que ocorra reflex\u00e3o total na interface vidro-ar\u00a0 —\u00a0 senL=sen\u03c6=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>=1\/n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 sen\u03c6=1\/n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.1\/n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>\u00a0= 1.sen\u03b2 (II)\u00a0 —\u00a0 sen\u03b2=1 (IV)\u00a0 —\u00a0 \u03b2=45<\/b><\/span><\/span>o<\/b><\/span><\/span><\/sup>\u00a0 —\u00a0\u00a0 n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>.sen\u03b8<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>= n<\/b><\/span><\/span>vidro<\/b><\/span><\/span><\/sub>.sen\u03c6 (I)=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>.sen\u03b2=1 —\u00a0 n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>.sen\u03b8<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>=1\u00a0 —\u00a0<\/b><\/span><\/span>\u00a0n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>=1\/sen\u03b8<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>.<\/b><\/span><\/span>\"\"<\/p>\n

b) n<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0= c\/V<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 1\/sen \u03b8<\/b><\/span><\/span>c<\/b><\/span><\/span><\/sub>= c\/V<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0 1\/0,75=3.10<\/b><\/span><\/span>5<\/b><\/span><\/span><\/sup>\/V<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0 —\u00a0\u00a0<\/b><\/span><\/span>V<\/b><\/span><\/span>\u00e1gua<\/b><\/span><\/span><\/sub>\u00a0= 2,25.10<\/b><\/span><\/span>5<\/b><\/span><\/span><\/sup>km\/s<\/b><\/span><\/span>.<\/b><\/span><\/span><\/p>\n

39-<\/b><\/span><\/span><\/span> \u00a0<\/b><\/span><\/span><\/span>I. Correta\u00a0 —\u00a0 quanto mais refringente \u00e9 o meio, maior ser\u00e1 o valor de n, \u00a0menor a velocidade da luz nesse meio e menor ser\u00e1 o \u00e2ngulo de refra\u00e7\u00e3o, ou seja, quanto maior o \u00edndice de refra\u00e7\u00e3o de um meio, mais o raio de luz se aproxima da normal\u00a0 —\u00a0 o menor \u00edndice de refra\u00e7\u00e3o \u00e9 o da glicerina.<\/b><\/span><\/span><\/p>\n

<\/a> II. Falsa\u00a0 —\u00a0 veja I.<\/b><\/span><\/span><\/p>\n

III. Correta\u00a0 —\u00a0 o valor do \u00e2ngulo limite \u00e9 dado por senL=n<\/b><\/span><\/span>menor<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>maior<\/b><\/span><\/span><\/sub>\u00a0(maior senL>L)\u00a0 —\u00a0 acr\u00edlico para o ar \u2013 senL\u2019=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>acr\u00edlico<\/b><\/span><\/span><\/sub>=1\/1,490 senL\u2019=0,67\u00a0 —\u00a0 zirc\u00f4nio para o ar \u2013 senl=L\u2019\u2019=n<\/b><\/span><\/span>ar<\/b><\/span><\/span><\/sub>\/n<\/b><\/span><\/span>zirc\u00f4nio<\/b><\/span><\/span><\/sub>=1\/1,920 senL\u2019\u2019=0,52\u00a0\u00a0 —\u00a0\u00a0 senL\u2019>senL\u2019\u2019\u00a0 —\u00a0 L\u2019>L\u2019\u2019.<\/b><\/span><\/span><\/p>\n

IV. Falsa\u00a0 —\u00a0 O \u00edndice de refra\u00e7\u00e3o de um mesmo meio depende da cor da luz monocrom\u00e1tica que nele viaja, ou seja, para cada cor ele tem um valor diferente.<\/b><\/span><\/span><\/p>\n

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

40-<\/b><\/span><\/span><\/span> <\/b>Para que ocorra reflex\u00e3o total no interior da fibra a luz deve incidir com um \u00e2ngulo \u03b8 tal que sem \u03b8 > sem L, onde L \u00e9 o \u00e2ngulo limite e fornecido por senL=nmenor\/nmaior\u00a0 —\u00a0 sen\u03b8 > 1,45\/1,60\u00a0 —\u00a0 sen\u03b8 > 0,91\u00a0 —\u00a0 consultando a tabela fornecida voc\u00ea verifica que \u03b8 = 65o\u00a0 —\u00a0 assim, para que a luz permane\u00e7a no interior do n\u00facleo o \u00e2ngulo \u03b8 deve ser aproximadamente de 65o\u00a0 —\u00a0\u00a0R- E<\/b><\/span><\/span><\/p>\n

 <\/p>\n

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

Resolu\u00e7\u00e3o comentada dos exerc\u00edcios de vestibulares sobre Reflex\u00e3o Total     01- Se ele incide com \u00e2ngulo limite (\u03b8=L), ele emerge rasante\u00a0\u00a0R- A 02- R- E 03- R- C\u00a0 —\u00a0 nos outros casos estaria passando de um meio de menor \u00edndice para um meio de maior \u00edndice e haveria refra\u00e7\u00e3o. 04- (01) Falsa \u2013 \u00e9 baseado na lei de Snell-Descartes<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2199,"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-2203","page","type-page","status-publish","hentry"],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2203","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=2203"}],"version-history":[{"count":3,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2203\/revisions"}],"predecessor-version":[{"id":10958,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2203\/revisions\/10958"}],"up":[{"embeddable":true,"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/pages\/2199"}],"wp:attachment":[{"href":"https:\/\/fisicaevestibular.com.br\/novo\/wp-json\/wp\/v2\/media?parent=2203"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}