121
Cahaya dan Optika
4. Sudut Kritis dan Pemantulan Sempurna
5711 25A91 C1=1; 25A;91D1 ;5C9;1 3181H1 :1CD8 141 5A=D;11H15711141B11CC5A9;=1C181A9:11A1H125A1B1
C1=1;B55AC9C5A751719A141;54D175:119B9;1C5AB52DC3181H1 =5711=9 5=1CD1 B531A1 B5=DA1 1719=11 5=1CD1
B5=DA1411CC5A:1495A81C9;104 1=21AC5AB52DC=5D:D;;13181H125A75A1;41A9=549D=5298
A11C;131;5=549D=;DA17A11CD41A11C1D41A9=549D=25A945;B 291B529825B1A;5=549D=25A945;B291B5298;539B589771B91A291BH1
=5:1D8971A9B?A=1 5C9;1BD4DC41C17?BD4DC291BH1:D71?B55AC949CD:D;;1
?58B91A 5=D491141B11CBD4DC41C17495A25B1AB91A
B91A 41B91ABD4DC291BD25AC1=21825B1A1C1DB5=1;9=5:1D89
71A9B?A=1 141B11C25B1ABD4DC41C17C5AC5CDH1;9B55AC9B91A 3181H149291B;1JC5A814171A9B?A=1B589771B91A291BH1B5:1:1A
45715A=D;112941721C1B=549D=;131D41A1 141;51411 B55AC999BD4DC41C1749B52DCBD4DC;A9C9B
571;1C119BD4DC;A9C9B14118BD4DC41C17;5C9;1B91A41C17 49291B;1B525B1AJ 9;1BD4DC41C17495A25B1A179=552989BD4DC;A9C9B
3181H1C941;1;149291B;1=519;1491CD;1B531A1B5=DA1 AC9H13181H1C941;1;1;5D1A41A9=549D=;131B55AC949CD:D;;1
?58B91A 5A9BC9F19918H1749B52DC5=1CD1B5=DA1 5A41B1A;1 81 C5AB52DC 411C 49B9=D;1 218F1 5=1CD1
B5=DA181H1C5A:149:9;1=5=5D894D1BH1A1C25A9;DC 1 181H141C1741A9=549D=5298A11C;5=549D=;DA17A11C
2 ,D4DC41C17529825B1A41A9141BD4DC;A9C9B
Gambar 6.23
Deskripsi geometri tentang sudut kritis dan pemantulan sempurna
n
2
n
1
n
1
n
2
1 2
3 4
5 6
i
udara kaca
i i
i r
r r
r i
r
Aktivitas Fisika 6.3
Sepotong plastik transparan terapung dipermukaan air. Agar
sinar datang seperti pada gambar di atas dipantulkan sempurna oleh
permukaan batas plastik air. Jika indek bias plastik n
k
dan indek bias air n
a
, berapa besar sudut ?
Tantangan
untuk Anda
udara
air plastik
Pemantulan Sempurna Tujuan Percobaan
Mengamati pemantulan sempurna.
Alat-Alat Percobaan Gelas minum, lilin, dan air.
Langkah-Langkah Percobaan 1.
Isilah gelas minum dengan air sampai hampir penuh. 2.
Letakkan gelas tersebut di pinggir meja. 3.
Nyalakan lilin pendek dan letakkan dekat dengan gelas.
4. Perhatikan gambar berikut.
Amati dari arah yang berseberangan dengan lilin dari arah agak di
bawah permukaan.
5. Apa yang dapat Anda amati?
6. Apa kesimpulan Anda dari kegiatan ini?
A9B95=1CD1B5=DA149=1611C;1411=C5;??79;?=D9 ;1B9H1;9141B5A1C?C9;.,-0 B55AC914104
,5A1C
?C9;14118BD1CDB5A1C81DBC5A2D1C41A91BC9;1C1D;131H17497D1;1 DCD;=5H1DA;13181H11C1D75?=21755;CA?=175C9; ,5A1C?C9;
C5A49A91C1B217919C94121791D1AB5217195=2D7;DBH1 17919C9 C5A2D1C41A9;131H17=5=99;9945;B291BC97794125A;D19C1B219;
mata pengamat
122
Mudah dan Aktif Belajar Fisika untuk Kelas X
Gambar 6.24
a Pemantulan sempurna pada serat optik.
b serat optik.
a b
Contoh
6.8
9CD7BD4DC;A9C9B25A91H17=5=99;9945;B291B=DC1;
141B11C495C1;;1 49D41A1
9 9;5C18D9
+ +
B9 +
+
;
J 149BD4DC;A9C9B25A9114118
J
B9 B9
+ 5 +
1C1D B9 +
+ L
5C5A171
;
BD4DC;A9C9B
1 1
sin t
i r
5 Pembiasan pada Kaca Plan Paralel
13111A1514118B5;597;131H17;54D1B9B91:17H1 492D1CB5:1:1A 131 1 1A15 411C 497D1;1 DCD; =571=1C9
:11H1B91AH17=5711=95=291B141DCD;=55CD;1945;B 291B;131C5AB52DC
,91A 41C17 41A9 D41A1 =55F19 ;131 B5C521 3= ;5=D491 =5D:D=549D=D41A1;5=219 141A?B5BC5AB52DCB55AC9C1=1;141
04
4104
591A=5711=95A75B5A141A91A18 B91AB5=D1 5B1AH15A75B5A1B91AC5AB52DC411C4989CD7B52171925A9;DC
5A81C9;1 B9
6 .
L 45;B291BH17C97791;1=571;921C;1BD4DC;A9C9B;539B589771
B91A41C174571BD4DC41C17H17C941;C5A1D25B1A1;1=5711=9 5=1CD1B5=DA1
1791D1AH17=5AD1;15=2D7;DBC5A2D1C41A91BC9;1C1D =1C5A9119H1725A6D7B9=594D79217919C9 58;1A513181H1
1C1D75?=21755;CA?=175C9;H17=1BD;;5411=B5A1C?C9;=5 711=95=1CD1B5=DA1141B11C;5D1A41A9B5A1C?C9;55A79
3181H1C941;21H1;H178917 5A41B1A;1819CD:9;1H1749;9A9= 14118B9H1B9H1;?=D9;1B9411=25CD;75?=2173181H1141
B11C49C5A9=149C5=1CCD:D1B9H1C5AB52DCB1=19B531A1DCD8C11 21H1;;58917155A79 5A41B1A;1141A?B5BC5A:149H15=1
CD1B5=DA1411C49C5CD;1D125B1AH1BD4DC;A9C9BDCD;4D1 =549D=C5AC5CDB52171925A9;DC
141B11CC5A:1495=1CD1B5=DA125A1;D5AB1=1125A9;DC
Gambar 6.25
Seberkas cahaya memasuki kaca plan paralel
d D
B A
O t
r
2
r
1
i
1
Gambar 6.26
Pergeseran arah sinar pada kaca plan paralel
B9 B9
+ . +
4571+ +
41.JB589771
123
Cahaya dan Optika
1
cos d
r
L 5A41B1A;1
495A?58 3?B
.
5A41B1A;14501
;414501
;495A?58 3?B
B9 .
6 . B58977125B1A5A75B5A1B91A
B9 L
3?B .
.
L 5C5A171
BD4DC41C17 C521;13111A15
. BD4DC291B
025B1A5A75B5A1B91A
,525A;1BB91A1B5A:1CD81415A=D;11;13111A15411C=5=25CD;BD4DC 41C17B525B1AJ 9;1C521;13111A153=41BD4DC291B
JC5CD;125B1A
5A75B5A1H174911=9?58B91A1B5AC5AB52DC 9
9;5C18D9 J.
J3=
B9 L
3?B .
. B9 J L
J
3?B
J
149;5C9;1=55F1C9;13111A15B91A1B5A=5711=95A75B5A13=41A9 1A18B5=D1
Contoh
6.9
6. Pembiasan pada Prisma
A9B=1=5AD1;12541H17C5A2D1C41A9751BC5=2DB3181H1CA1B 1A1H17;54D1B9B9H14921C1B9294175A=D;1H17A5=25CD;BD4DC
C5AC5CD B1CD B1=1 19 ,D4DC C5AB52DC 491=1;1 BD4DC 5=291B B9=2? 94175A=D;11A9B=125A6D7B9B521719294175=291B
5A81C9;1:11H1B91AH17=55F1C9B52D18A9B=114104 181H141C1741A9D41A1=5D:D294175A=D;11A9B=11;1
49291B;1=545;1C971A9B?A=1 5=D491;5C9;13181H1=59771;1 A9B=1=5D:DD41A13181H1C5AB52DC1;149291B;1=5:1D8971A9B?A=1
,5C518=55F1C9A9B=13181H1=5711=945E91B9 5B1AH1BD4DC45E91B9 H174911=93181H114118B52171925A9;DC 5A81C9;104
5A81C9;1 . 6
41
6 .
J 6 6
5A81C9;1
J .
1
J .
2
Gambar 6.27
Prisma segitiga
Gambar 6.28
Jalannya sinar pada prisma N
N sinar
datang sinar
bias
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