lensa cermin dan gelombang
TRANSCRIPT
Keywords (kata kunci)
Ligght theory (teori cahaya)
Reflection of light (pemantulan cahaya)
Mirror (cermin) Mirror equation
(persamaan cermin) Image formation
(pembentukan bayangan)
Refraktion of light (pembiasan cahaya)
Refractive index (indeks bias)
Lens (lensa) Lens equation
(persamaan lensa) Optical instruments
(alat-alat optik) Electromagnetic waves
spectrum (spektrum gelombang elektromagnetik)
A. Nature of Light (sifat dasar cahaya)Sifat cahaya ada dua, yaitu:
1. Cahaya sebagai gelombang (waves)2. Cahaya sebagai partikel (particles)
1. Emission of Light (Pancaran Cahaya)
Elektron
Cahaya dipancarkanLight is emited
Inti
Excited stateKeadaan tereksitasi
Lower energy levelTingkat energiLebih rendah
Lowest energy levelTingkat terendah
+
2. Electromagnetic Waves (gelombang Elektromagnetik)Cahaya polikromatik (polychromatic light) adalah cahaya yang terdiri dari berbagai panjang gelombang dan frekuensi.contoh : cahaya matahari (sunshine)cahaya monokramatik (monochromatic light) adalah cahaya yang hanya terdiri dari satu panjang gelombang dan frekuensi.contoh : laser
Dengan: v = c = light speed (laju cahaya)
= 3 x 108 m/s = wavelength/panjang gelombang
(m) f = frequency/frekuensi (Hz)
3. Photon (foton)adalah paket-paket energi cahaya atau energi yang dibangkitkan oleh gerakan muatan-muatan listrik (radiasi elektromagnetik)Foton merupakan partikel-partikel yang tidak bermuatan listrik dan tidak bermassa,tetapi mempunyai energi dan momentum.
Besarnya energi sebuah foton dirumuskan:
Dengan : E = photon energy
(J) h = Planck’s
constant = 6,63 x 10-34 Js f = frequency (Hz) 1 eV = 1,6 x 10-19J
hfE
Contoh soal
Calculate the amount of photon emitted by a 100 watt lamp in 2 second, if the light that radiated by the lamp has wavelength of 600 nm!
Diket : P = 100 watt t = 2 s = 600 nm = 600 x 10-9m c = 3 x 108 m/s h = 6,63 x 10-34 Js
Ditanya: n
4. Interaction of Light with substances(interaksi cahaya dengan bahan)
a. Transparent Subtstances (bahan tembus cahaya)
lens
c. Translucent Substances (bahan buram)- meneruskan- memantulkan- menyerap- menghamburkancontoh : air keruh
5. Interference, Diffraction, and Polarization (interferensi, difraksi, dan polarisasi)
a. Interference (Interferensi)adalah sebuah peristiwa yang terjadi ketika dua buah gelombang bertemu pada saat bergerak dalam medium yang sama.Interferensi gelombang ada 2 yaitu: interferensi konstruktif dan destruktif
b. Difraction (difraksi)Pembelokan atau penyebaran gelombang cahaya ketika cahaya tersebut dilewatkan melalui celah sempit.contoh : difraksi sinar – x oleh kisi kristal padat
c. Polarization proses pengubahan cahaya tak terpolarisasi menjadi cahaya terpolarisasi.Proses polarisasi:- transmisi- pemantulan- pembiasan- hamburan menggunakan polaroid filter.
6. The development of Theories of Light (Perkembangan Teori-teori Cahaya)
a. Impuls Theory of Light (teori impuls cahaya)
b. Corpuscular Theory (teori Korpuskuler)
c. Waves Theory (teory gelombang)d. Theory of Electromagnetic Waves
(teori gelombang elektromagnetik)e. Quantum Theory (teori kuantum)
B. Reflection of Light (Pemantulan Cahaya)
1. Stremam of Ligth (Berkas cahaya)
Source of lightSumber cahaya
Waves frontMuka gelombang
Rays/sinar
Kinds of stream of ligth (jenis-jenis berkas cahaya)
Parallel/sejajar
DivergingMenyebar
Converging mengumpul
2. Types of Light Reflection (jenis-jenis pemantulan cahaya)
Specular Reflection(smooth surfaces)
Diffuse Reflection(rough surfaces
3. The Law of Light Reflection (Hukum Pemantulan cahaya)
I R
i R
N
I = incident ray sinar datang
R = reflected ray sinar pantul
The Law of light reflection:a. Incident ray, reflected ray, and the
normal line cut at one point and lie on one straight plane.
b. The angle of incidence (i) is equal to the angle reflection (R)
I = R
4. Reflection of Light on Plane Mirrors (Pemantulan pada Cermin Datar)
a. The Characteristics of Image on Plane Mirrors (Sifat-sifat Bayangan pada Cermin Datar)
1) Cannot catched by screen (virtual image) (bayangan maya)
2) Upright and face invertedly to the object (tegak dan menghadap berlawanan arah terhadap bendanya)
3) The image is equal in size as the object (bayangan sama besar dengan bendanya)
4) The image distance to the mirror is equal to the object distance to the mirror (jarak bayangan ke cermin sama dengan jarak benda ke cermin)
S S’
b. Drawing Image Formation in Plane Mirrors with Ray Diagram (melukis pembentukan bayangan pada cermin datar dengan diagram sinar)
c. The Sum of Image on Plane Mirror (jumlah bayangan pada cermin datar)
mn
0360
Contoh
Two plane mirrors form an angle of 90o of each. If an object is placed between both mirrors, determine the sum of image formed!
5. Reflection in Curved Mirrors (Pemantulan pada cermin Lengkung)
a. The Anatomy of Concave and Convex Mirror (anatomi cermin cekung dan cermin cembung)
OFM
OF M
R RConcave mirror Convex mirror
1) Special Rays in Convave Mirrors (sinar-sinar istimewa pada cermin cekung)
a) The incident ray parallel to the principal axis will be reflected passing through the focal point.
OFM
+
b) The incident ray passing through the focal point will be reflected parallel to the principal axis.
OFM
+
c) The incident ray passing through the mirror’s center of curvature will be reflected again through the same point.
OFM
+
2) Drawing Image Formation in Concave Mirrors with Ray Diagrams (melukis pembentukan bayangan pada cermin cekung dengan diagram sinar)
3) Spherical Aberration (Aberasi Sferis)
FM
1) Special Rays in convex Mirrors (Sinar-sinar Istimewa pada Cermin Cembung)
a) The incident ray parallel to the principal axis will be reflected as if it comes from the focal point.
F MO
2) The incident ray that seems to wards the focal point will be reflected parallel to the principal axis.
F M
c) The incident ray that seems to wards the mirror’s center of curvature will be reflected as if it comes from that point.
F M
2) Drawing Image Formation in Convex Mirrors with Ray Diagram (Melukis Pembentukkan Bayangan pada Cermin Cembung dengan Diagram Sinar)
d. Esbach’s Theorem (Dalil Esbach)
OFM
III II I IV
+
CONCAVE MIRRORS
O F M
IV I II III
-
CONVEX MIRRORS
The image characteristics of concave and convex mirrors can be determined based on Esbach’s theorem according to the rules as follows:
1. R + R’ = 5
2. All images in front of the mirrors are real and inverted.
3. All images behind the mirrors are virtual and upright.
4. R’ R (then the image is magnified)
5. R’ R (then the image is reduced)
Where: f = mirror focal length (panjang
fokus cermin) S = object distance to the mirror
(jarak benda ke cermin) S’= image distance to the mirror
(jarak bayangan ke cermin) R = mirror’s radius of vurvature
(jari-jari cermin) = 2f
Note (catatan) In the curved mirror equation, there
are rules of mark, those are: f and R is positive (+) for concave
mirrors f and R is negative (-) for convex
mirrors S is positive (+) if the object is in
front of the mirror and s is negative (-) if the object lies behind the mirror.
S’ is positive (+) if the image lies is in front of the mirror and s’ is negative (-) if the image lies behind the mirror.
Linear magnification is defined as the ratio of image height (h’) with object height (h), this magnification is formulated by the following equation.
s
s
h
hM
''
Where: M = linear magnification
(perbesaran linier) h’ = image height (tinggi
bayangan) h = object height (tinggi benda)
Sample Problem
1. A convex mirror has focal length of 20 cm. If an object lies 10 cm in front of the mirror, determine:
a. Image distance to the mirrorb. Image linier magnification.
2. An object of 2 cm in height stands upright in front of a concave mirror which has the focal length 10 cm. If the object distance to the mirror 15 cm, ditermine:
a. Image magnification b. Image height
f. Problem Solving of Two Mirrors which Face Each Other (Penyelesaian Masalah Dua Buah Cermin yang saling Berhadapan)Secara matematis jarak antar cermin dirumuskan:
2'1 ssd
Where: d = distance between mirror (jarak
antar cermin) s1’ = first image distance to the
first mirror (jarak bayangan pertama ke cermin pertama)
S2 = first image distance to the second mirror (jarak bayangan pertama ke
cermin ke dua)
The final image resulthan from the curved mirror system that face each other has the total magnification as follows.
2
'2
1
'1
21 s
sx
s
sxMMM tot
Refraction of Light(Pembiasan Cahaya)
1. The Definition of Light Refraction (Pengertian Pembiasan Cahaya)Pembiasan cahaya adalah: peristiwa pembelokan arah cahaya ketika meliwati bidang batas diantara dua medium yang berbeda.
Pada Pembiasan cahaya terjadi: Perubahan arah Perubahan kecepatan Perubahan panjang gelombang Frekuensi dan fase gelombang tetap
2. The Law of Refraction (Snell’s Law)1. Snell’s I law:
“The incident ray, refracted ray and normal line all lie on one plane”
2. Snell’s II law:“If the incident ray travels from a less dense to a denser medium, then it bends (refracts) towards the normal line, and if the incident ray travels from a denser to a less dense medium then it bends (refracts) away from the normal line.
Secara matematis dirumuskan:
2211 sinsin nn
Where:n1 = refractive index of medium 1
n2 = refractive index of medium 2
Θ1 = angle of incidence
Θ2 = angle of refraction
3. Refractive Index (Indeks Bias)1. Absolute refractive index
v
cn
Where:n = absolute refractive indexc = light speed in air = 3 x 108 m/sv = light speed in medium (m/s)
When light travels a certain medium to another medium and is refracted, then it has different speed in the two medium. Therefore, holds the following eqution.
212
1
1
2
2
1 nn
n
v
v
Sample Problem
A stream of light travels from air to a glass with the angle of incidence 60o, if nair = 1 and nglass = 3, determine the angle of light refraction!
The speed of light in air 3 x 108 m/s and its frequency 6 x 1014 Hz, determine:
a. Light speed in water (n = 1,33)b. The change of wavelength in water and in
air
Scientific Activity(Kegiatan Ilmiah)
Refraction of Light in Planparallel Glass( Pembiasan cahaya pada kaca Planparalel)
Refraction of Light in Prism (Pembiasan Cahaya pada Prisma)
Total reflection can occur if the following two conditions are complied, those are, light travels from a denser to a less dense medium and the light angle of incidence is larger than the critical angle.
1
2
21
sin
90sinsin
n
n
nn
k
ok
Where : n1 = refractive index of medium 1 (denser
medium) n2 = refractive index of medium 2 (less dense
medium) k = critical angle
Reflection of Light in Planparallel Glass
(Pembiasan pada Kaca Planparallel)N1 N2
d
n1
n2 n1
n1
1
2
t
1’
2’
Where: t = displacement of light d = planparallel glass thickness 1= angle of incidence
2= angle of refraction
Based on the figure above, then the refraction in prism the following equations:
41
32
D
and
Where: = angle of refrator1 = first angle of incidence2 = first angle Of refractionD = deviation angle3 = second angle of Incidence4 = second angle of refraction
Because at the moment of minimum deviation 1 = 4, then 2= 3, so that 1= ½ ( + Dm), and = 22 = 23
Then, Snell’s law equation: 2
121 sinsin pmm nDn
Where :nm = refractive index of medium
np = refractive index of pris
Sample problem
The ray of light shown in Figure 1 is incident upon a 600-600-600 glass prism, n = 1,5
1=450
2 1’
2’
600
600 600
P Q
a. Using Snell’s law of refraction, determine the angle 2, the nearest degree.
b. Using elementary geometri, determine the value of 1’
c. Determine 2’
A light hits one surface of a thick glass by angle of incidence 600. If the refraction index of glass 1,5, then calculate the angle formed by the light coming out from the glass to the normal line!
Refraction of Light in Curved Plane
(Pembiasan Cahaya pada Bidang Lengkung)
Light refraction in curved plane
s
S’
n1 n2
Mathematically, the image formation in transparent curved plane complies the following equation:
R
nn
s
n
s
n 12,21
Where:n1 = refractive index of medium 1n2 = refractive index of medium 2S = object distance to the curved plane surfaceS’ = image distance to the curved plane surfaceR = radius of curvature
While the magnification of image formed can be ditermined by the following equation:
2
1''
n
nxs
s
h
hM
Where:M = image magnificationh’ = image heighth = object height
The value of R, s and s’ from the above equtions comply the following rules: R positive (+) if the surface of plane is
convex and R negative (-) if the surface of plane is concave.
S positive (+) for real object and s negatif (-) for virtual object.
S’ positive (+) for real image and s’ negatif (-) for virtual image.
Based on the figure above, for s = f1, then s’= ~, therefore the object focal length (f1) can be determined as follows:
12
11
1
12
1
121
1221
,
nn
Rnf
thenfs
because
nn
Rns
R
nn
s
nR
nnn
s
n
Where:f1 = object focal
length