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1. CHAPTER VICHAPTER VI
ALAT OPTIKALAT OPTIK

2. A. Index of Refraction
1. The absolute index of refraction
“ the ratio between light speed in the vacuum (c) and the
speed of light in that medium (v)”
n= absolute Index of refraction of the medium
v= Speed of light in the medium
c= Speed of light in free space (vacuum) = 3 x 108
m/s
2. The relative Index of refraction
v
c
n =
)r(Sin
)i(Sin
v
v
n
n
n
2
1
2
1
1
2
21 =
λ
λ
===
i
r
n1
n2
λ1
v2
λ2
v1

3. • n21 = The relative Index of refraction from the medium 2 to medium 1
• n1, n2 = The absolute Index of refraction of medium 1, medium 2
• λ1 , λ2= The wave length of light in medium 1, medium 2 (m)
• v1, v2 = Speed of light in medium 1, medium 2 (m/s)
1. If the absolute index of refraction of air, water , glass and diamond each is 1,
4/3, 3/2 and 5/2. Find :
a. The relative index of refraction from water to glass
b. The relative index of refraction from diamond to glass.
c. Speed of light in water, glass and diamond (c = 3 x 108
m/s)
d. The wave length green light in water, glass and diamond (if the wave length
green light in air is 5000Ao
)
e. The green light frequency
f. If a light ray enters from air into water at an angle 45 o.
Find an angle of
refraction in water.
Problems:
2. A path of yellow rays with a wave length of 550 nm strikes into water ( n water= 4/3 ).
Find: a. The speed of the light in water.
b. The wave length and frequency of the light in water

5. LENSES
The definition : a transparent material which is limited by spherical surfaces or
spherical and plane surfaces.
The kind of lenses: converging lenses (+ ) and diverging lenses ( - )
F(virtual)( - )
F(real) ( + )
The Properties of covex lenses :
1.To converge rays
2.The focus of the lenses is real ( + )
3. On the centre part is thicker
The Properties of concave lenses :
• To diverge rays
• The focus the lenses is virtual ( - )
• On the centre part is thinner

6. PRINCIPAL RAYS FOR LENSES
a. Pricipal rays for Converging Lenses
1. Rays parallel to the principal axis pass trough the principal focus
after trough the lens.
2. Rays coming from the principal focus emerge parallel to the
principal axis after refraction trough the lens.
3. Rays passing trough the optical centre are not deviated.
F22.F2 F1 2.F1
1
2
3
O
1. sejajar SU ~ F1
2. F2 ~ sejajar SU
3. O ~ tidak membelok

7. b. Principal Rays for Diverging Lenses
• Rays parallel to the principal axis are refracted and the
extension of the refracted rays passes trough the focus.
• If rays are incident on the lens in such a way that their
extension pass trough the focus, they are refracted parallel
to the principal ( optical ) axis.
• Rays passing trough the optical centre are not deviated.
F1 2F1F22F1
1
2
3

8. ( + )

9. III. ALAT OPTIK
Akomodasi Maksimum: Kondisi lensa mata
menyembung (fokus lensa mengecil), Mata melihat benda pada
jarak paling dekat (Benda di titik dekat = punctum procximum =
PP, untuk mata normal = 25 cm ).
Akomodasi Minimum : Kondisi lensa mata memipih
(fokus mengecil). Mata rileks. Mata melihat benda pada jarak
terjauh (Benda di titik jauh = punctum remotum = PR ).
1.
MATA

10. Jangkauan Penglihatan
• Mata Normal
• Rabun Jauh
(miopi)
• Mata tua
(Presbiopi)
• Rabun dekat
(hipermetropi)
25 cm
∞
PP
PP
PP
PP
PR
PR
PR
PR

11. Ada 3 kategori kondisi mata saat memakai
alat optik.
“ kondisi mata ini tergantung pada letak bayangan yang
dihasilkan oleh alat optik tersebut”
1. Mata akomodasi maksimum: Terjadi saat bayangan
yang dihasilkan alat optik tersebut terletak di titik dekat
mata, PP ( s’ = - PP)
2. Mata akomodasi minimum: Terjadi saat bayangan
yang dihasilkan alat optik tersebut terletak di titik jauh
mata, PR ( s’ = - PR, untuk mata normal s’= ~)
3. Mata akomodasi pada jarak X Terjadi saat bayangan
yang dihasilkan alat optik tersebut terletak sejauh jauh
X dari mata ( s’ = - X)

12. 2. Kacamata
Menentukan kekuatan lensa kacamata:
A. Rabun jauh (dibutuhkan kacamata lensa negatif)
• Jika setelah pakai kacamata jarak lihat terjauh menjadi X
)(
1
mf
P =
Hitung fokus (f) dengan
persamaan :
s’
1
s
1
f
1 +=
dimana:
S= x (jarak lihat terjauh setelah pakai kacamata)
S’= - PR (jarak lihat terjauh sebelum pakai kacamata)
Hitung kuat lensa dg
persamaan:

13. • Jika setelah pakai kacamata jangkauan penglihatannya
normal ( titik jauh: ~)
)(
-1
mPR
P =
)(
-100
cmPR
P =atau
B. Hipermetropi/rabun dekat (dibutuhkan kacamata
lensa positif)
• Jika setelah pakai kacamata jarak lihat terdekat menjadi X
s’
1
s
1
f
1 +=
dimana:
S= x (titik dekat mata setelah pakai kacamata)
S’= -PP (titik dekat mata sebelum pakai kacamata)
Hitung fokus (f) dengan
persamaan :

14. ).(
1
4
cmPP
P −=
).(
100
4
cmPP
P −=
C. Mata Tua (dibutuhkan lensa positif dan negatif)
• Jika setelah pakai kacamata jangkauan penglihatannya
normal ( titik dekat: 25 cm)

15. 3. Kaca Pembesar/LUP
1. merupakan lensa (+)
2. benda harus diletakkan di ruang I (O - F)
3. bayangan di ruang IV dengan sifat maya, tegak, dan
diperbesar.
Kondisi mata saat pakai LUP.
1. Akomodasi maksimum:
Letak benda: antara O – F (0 < s < f)
Letak bayangan: S’= - PP = -Sn = - 25 cm
M =
PP
f
+ 1

16. 2. Akomodasi minimum;
Letak benda : tepat dititik fokus, S = f
Letak bayangan :S’ =
3. Akomodasi pada jarak tertentu (X);
Letak benda : antara O - F
Letak bayangan :S’= - X
~
M =
PP
f
=
PP
f
+
X
PP
M

17. Diagram cahaya pada LUP.
a. Untuk Mata Akomodasi Maksimum
F1
2 F2 2 F1
(+)
h
h’
S
F2
S’ = -PP

18. b. Akomodasi pada jarak X
F1
2 F2 2 F1
(+)
h
h’
S
F2
S’ = - X

19. c. Akomodasi minimum
F2
2 F1F1
2 F2
S’ = ~
S

20. 4. Microscope
Untuk melihat benda kecil agar tampak besar dan
jelas
Terdiri dari 2 lensa positif: obyektif dan okuler
 fob < foc
 Sifat bayangan oleh lensa obyektif : nyata, terbalik,
diperbesar.
 Sifat bayangan oleh lensa okuler: maya, tegak,
diperbesar

22. The ray diagram of Microscope
a.Min Accommodation
Fok
F ok
Oc. L. ( + )Ob. L.(+)
Sok
S’ob
Sob
d

23. b. Max Accommodation
Fob Fok
Oc. L. ( + )Ob. L ( + )
S’ok= -PP
Sok
Sob
S’ob
Fok
d

24. and than, Mok depends conditions of the eyes when
using the microscope; .
1. For Maximum Accommodation:
Location of the final image: Sok’= - PP =-Sn = - 25 cm
Mok=
PP
fok
+ 1
Microscope Magnification
Mtotal = Mob x Mok
Where: Mob
=
S’
ob
S ob
d = s’ob + sok
obtain

25. 2. For Minimum Accommodation
Location of the objects for ocular lens:Sok = fok
Location of the final image :Sok’ =
3. For Accommodation at certain distance (X);
Location of the final image :Sok’= - X
~
Mok =
PP
fok
=
PP
fok
+
X
PP
Mok
d = s’ob + fok
d = s’ob + sok
obtain
obtain
d = the microscope length(the distance of the objective lens to
the ocular lens)

26. 5. TELESKOP / TEROPONG
Untuk melihat benda jauh agar tampak dekat dan jelas
Karakteristik Teropong:
•Lokasi benda: tak terhingga(Sob = ~ )
•Letak bayangan oleh lensa obyektif: tepat di titik fokus
obyektif (S’ob = fob )
• fob > fok
•Terdiri dari 2 lensa ( + )
•Sifat akhir bayangan: maya, tegak, diperbesar
A. TEROPONG BINTANG

27. M =
f ob
S ok
d = f ob + S ok
Panjang teropong (d):
FobFok
Fok
a. Akomodasi Maksimum (s’ok= - PP)
S’ok
Sok
S’ob= fob
L. Okuler ( + )L. Obyektive(+)
Perbesaran (M):
Diagram cahaya:

28. M =
f ok
f ob
d = f ob + f ok
The telescope length :The magnification;
d
b. Min Accommodation (sok = fok)
Fob
F ok
Fok
Sok= fok
S’ob= fob
L. Obyektive(+) L. Ocular ( + )

29. B. Teropong BUMI
• Terdiri dari 3 lensa (+) : Obyektif, pembalik, okuler. .
OB (+) OK (+)
I (+)
Fok
F ob,
2FP F ok
d = f ob + 4 f P + s ok
M =
s ok
f ob
2FP
S’ob
4 fp
sok
 Diagram Sinar:
a. Maximum Accommodation (s’ok = -PP)

30. OB ( + )
OK ( + )
Pembalik (+)
F ok ,
F P
F ob,
FP
F ok
d = f ob + 4 f P + f ok
M =
f ok
f ob
b. Minimum Accommodation (sok = fok)

31. C. Teropong Panggung/Sandiwara/Gallileo
• Consists of one convex lens as an objective lense one concave
lense ( + ) as an eye piece lens ( - ).
• The objective lens ( + ) :
– The object is at infinitive ( S = )
– The image is at the focus point ( S’ = fouler )
• The eye piece lens ( - ) :
– Min accommodation.....
» the object is at focus ( Sok= fok )
» The image is at far point ( Sok = )
– Max accommodation ....
» the object is at the first region
» the image is at the near point ( S’ok = 25 cm )
• The final properties of the image are :
– Virtual
– inverted
– larger

32. The magnification Gallilean bioculars
okular
obj
ak
S
F
M =max
fob
fok