113
Cahaya dan Optika
Gambar 6.8
Bagian-bagian cermin cekung f = jarak fokus
R = kelengkungan cermin R
f O
B F
P
a b
c P
F O
Gambar 6.9
Sinar istimewa pada cermin cekung
Gambar 6.10
Pembentukan bayangan di ruang III AB pada cermin cekung
O B
F P
A A
B I
II III
5A41B1A;104
04
4104
411C 49B9=D;1218F1
1 :9;1 2541 141 AD17 =1;1 21H171 H17 4981B9;1 14118 =1H1C571;41495A25B1A
2 :9;1254125A14149AD17=1;121H171H174981B9;114118 H1C149AD17C5A219;41495A25B1A
3 :9;1254125A141141AD17=1;121H171H174981B9;1 14118H1C149AD17C5A219;41495A25B1A
Gambar 6.11
Gambar bayangan jika letak bendanya di ruang II
Gambar 6.12
Gambar bayangan jika bendanya di ruang I
O A
P A
B B
I II
III
F O
F A
P A
B B
I II
III
S S
b. Pemantulan pada Cermin Cekung
5A=935;D71411835A=9H17=5=99;95A=D;1135;D7 5A=935;D725AB961C;?E5A75H19CD25AB961C=57D=D;1B91A
17912179135A=935;D7C1=1;B55AC914104 0167.1:112+40,1.71
5C1;41B961C21H171H174925CD;?5835A=935;D725A71CD7 1415C1;2541 ,52D182541H17495C1;;149451B52D1835A=9
35;D71;1=5=99;921H1714571B961CB961CC5AC5CD 5A81C9;1 04
B961CB961C35A=935;D7491C1A1H1
1 ,91A41C17H17B5:1:1ABD=2DDC1=1491CD;1=51D9C9C9; 6?;DBDC1=1
2 ,91A 41C17 H17 =51D9 C9C9; 6?;DB DC1=1 491CD;1 B5:1:1A 4571BD=2DDC1=1
3 ,91A41C17H17=51D9C9C9;DB1C;557;D7135A=91;1 491CD;1;5=219=51D99C1B1H17B1=1
1H171B52D182541?5835A=935;D7411C49C5CD;14571 31A1=5771=21A;1
41A9B91A9BC9=5F114135A=935;D7 1A1
=5D;9B 21H171 2541 ?58 35A=9 35;D7 14118 B521719 25A9;DC 5A81C9;1 04
+ -.0 35A=9 35;D7 4971=21A
57;145712179121791H1 +1 71A9B 4971=21A DCD;=51=217;1C97792541 41D71A9BC941;5ADC5A1D
C9779 + 0 71=21A;1B91A9BC9=5F1L + -0 71=21A;1 B91A 9BC9=5F1L
+ C9C9; H17 =5AD1;1
5A?C?711C1A1B91A1CDL41B91A1CDL
4925A91=1 -9C9;99=5AD1;121H17141A9C9C9;5=D49171A9BC571;DADB
BD=2DDC1=149C1A9;41A9C9C9;;51A18BD=2DDC1=1 -9C9;994925A9 1=1H17=5AD1;121H17141A9C9C9;B589771=5AD1;1
21H17141A971A9B
114
Mudah dan Aktif Belajar Fisika untuk Kelas X
7711164-4.2.751-4,-4,.1.71140,1 D2D71 1C1A1 :1A1; 6?;DB 41 :1A9:1A9 ;557;D71 35A=9
411C4931A945715AC??7104 14171=21AC5AB52DCC1=1;218F1B91AB5:1:1ABD=2DDC1=141C17
;55A=D;1135A=935;D7;5=D491491CD;1=51D9C9C9;6?;DB ,91AB91A99=579;DC98D;D=5=1CD1H19CDBD4DC41C17B1=1
4571BD4DC1CD 58;1A519CDB579C971=5AD1;1B579C971 B1=1;1;9B9B9
B9B99;1B91A41C1745;1CB5;194571BD=2D
DC1=1411C491771B1=14571B589771
1A9B99 495A?58218F1
1C1D
5C5A171 :1A1;6?;DB
:1A9:1A9;557;D7135A=9 7075340,1.71
,519 B531A1 75?=5CA9 5C1; 41 B961C 21H171 2541 411C 49C5CD;1B531A15A89CD7145715AB1=11B52171925A9;DC
5A81C9;104 14104
C1=1;218F1
41 B5217D
B589771
58;1A51 =1;1
L L
’ ’
h s
h s
L 14104
C1=1;218F1
41 B5217D
.CD; 25A1;D
C1 6
.CD; 25A1;D
C1 6
B589771 6
6 6 6
58;1A51 =1;1 6
6 6
6
6
6 L
Gambar 6.14
Letak dan sifat bayangan benda pada cermin cekung
Gambar 6.13
Hubungan antara fokus dan jari- jari cermin cekung
P R
F
R f
A O
Keterangan: s = jarak benda ke cermin
h = tinggi benda f = jarak fokus
h = tinggi bayangan s = jarak bayangan ke cermin
571=577D1;15AB1=1135A=9C5AB52DC41411C=5 5CD;1:1A1;21H171B52D182541 41D5A25B1A121H171
Konvensi tanda untuk pemantulan: K s bernilai + jika objek berada di
depan cermin objek maya bernilai – jika objek di belakang
cermin objek nyata K s’ bernilai + jika objek berada di
depan cermin objek nyata bernilai – jika objek berada di
belakang cermin objek maya K r, f bernilai + jika pusat
kelengkungan berada di depan cermin cermin cekung
bernilai – jika pusat kelengkungan berada di belakang cermin
cermin cembung.
Ingatlah
B
A P
E D F
O f
s R
s h
h
115
Cahaya dan Optika
4945699B9;1B5217195A2149711C1A125B1AC977921H17141 25B1AC97792541 ,531A1=1C5=1C9B411C49CD9B
L
c. Pemantulan pada Cermin Cembung
5A=935=2D71411835A=9H17=5=99;95A=D;1135=2D7 5A=935=2D725AB961C49E5A75H19CD25AB961C=5=131A;1B91A
17912179135A=935=2D7B55AC914104 0167.1:112+40,1071
,52D182541H17495C1;;149451B52D1835A=935=2D7=5 =99;921H1714571B961CB961CC5AC5CD 1H171B52D182541?5835A=9
35=2D7411C49C5CD;1457131A1=5771=21A;1
41A9B91A9BC9=5F1 14135A=935=2D7 5A81C9;104
14104
C5A981C
1 B91A41C17H17B5:1:1ABD=2DDC1=1491CD;1B51;11;1 41C1741A9C9C9;6?;DB
2 B91A41C17H17=5D:DC9C9;6?;DB491CD;1B5:1:1A4571 BD=2DDC1=1
3 B91A41C17H17=5D:DC9C9;DB1C;557;D7135A=9491 CD;1;5=219=51D99C1B1H17B1=1
1A1=5D;9B21H1712541?5835A=935=2D7C5A981CB55AC9 14104
14131A1C5AB52DCB91A9BC9=5F1H17497D1;1
14118B91A41B91A 5A41B1A;171=21A21H171C5AB52DC411C 49B9=D;1218F12541H17495C1;;149451B52D1835A=935=
2D7B51D=5781B9;121H171=1H1C571;41495A;539 7075340,1071
+D=DB14135A=935=2D7B1=1B55AC9AD=DBH1725A1;D141 35A=935;D7H19CD
L
Gambar 6.15
Bagian-bagian cermin cembung R = jari-jari kelengkungan cermin
P = titik pusat kelengkungan cermin F = titik fokus cermin
f = jarak titik fokus ke cermin SU
O f
F P
R
O F
P
Gambar 6.17
Lukisan pembentukan bayangan oleh cermin cembung
a b
c
O F
P
Gambar 6.16
Sinar-sinar istimewa pada cermin cembung
181H175AD495A81C9;114118 1 C141:1A1;6?;DB14135A=935=2D7B51D25A919571C96 1
9949B5212;15C1;C9C9;6?;DB14135A=935=2D7C5A5C1;49 251;1735A=9
2 DCD; 2541 H1C1 49 451 35A=9 35=2D7 B51D C5A25CD; 21H171=1H1 14991914135A=935=2D725AC141571C96
,52D1835A=935;D7=5=99;9:1A9:1A9;557;D71
= ,52D182541495C1;;1141 :1A1;=41A935A=9C977925413= 9CD7185C1;C9779415A25B1A121H171
9 9;5C18D9
Contoh
6.4
2 DCD; 2541 H1C1 49 451 35A=9 35=2D7 B51D C5A25CD; 21H171=1H1 149919B14135A=935=2D725AC141571C96
