quantum physics -...
TRANSCRIPT
Quantum Physics
OVERVIEW
• Concept of Photon
• Blackbody Radiation and Planck’s Hypothesis
• Photoelectric Effect
• Compton Effect
• de Broglie Wavelength
• Relativity
Why we study this chapter?
Some application in light quantum physics
SOLAR CELL TECHNOLOGY
Theory of Light
WAVE PARTICLE
Light has both wave and particle
characteristic
Photoelectric Effect
Compton Effect
Blackbody Radiation
A black-body is any object that can absorb or emit radiation energy
Emissivity (𝑒) 0 ≤ 𝑒 ≤ 1
Perfect Reflector Perfect absorber or emitter
Reflects all radiation energy it received.
When absorbing, it will absorb all energy it receives. When emitting, it will emit all energy it has.
Example
Which of the following phrases correctly describes a perfectly
blackbody?
a. object from which neither light nor matter escapes
b. absorbs all radiation and emits no radiation
c. emits all radiation and absorbs no radiation
d. perfectly absorbs or emits all radiation
Concept of Photon
Light has an electromagnetic wave characteristic.
electromagnetic wave energy is emitted and absorbed by materials in the form of energy package called photons.
E = ℎ 𝑓
The energy of light can be stated as,
h = Plank’s Constant (6.63 x 10-34 J.s)
f = Photon’s Frequency (Hz)
𝑓 =c__λ
Example
A radio transmitter emits a wave of 15.08 MHz frequency. Calculate the energy of each photon of the wave. (h = 6.63x10-34 Js)
E = ℎ 𝑓
The energy of light can be stated as,
= (6.63𝑥10_34 Js)(15.08x106 Hz)
= 100 x 10-28 J
Example
Calculate the photon’s energy of an electromagnetic wave with 663 nm wavelength. (c = 3 × 108 m/s, h = 6.63 × 10–34 J.s)
E = ℎ𝑐
𝜆
The energy of single photon can be stated as,
= (6.63x10-34)(3𝑥108)
663𝑥10−9
= (10-34) (3x1015)
= 3x10-19 J
Photoelectric Effect
in 1887 Hertz observed a phenomenon during his experiments whichproved the existence of electromagnetic waves characteristic in light.
This phenomenon was the emission ofelectrons from a metal surface whenlight was incident upon it.
PHOTOELECTRIC EFFECT
The emitted electrons are calledphotoelectrons.
Photoelectric Effect
If the wavelength of light is held constant,an increase in light intensity causes anincrease in the number of electrons emitted.However, the kinetic energy of the emittedphotoelectrons does not change.
If the intensity of light is held constant,when the wavelength of light is changed,the number of emitted photoelectrons remainsthe same, but their kinetic energies change.
When a different metal is used,depending on the wavelength oflight, sometimes no emission isobserved.
Electrons are emitted from the surface almostinstantaneously.
Explained by Einstein in 1905
Photoelectric Effect
Energy of Photon =
Kinetic Energy of Electron
+Work
Function of Metal
The minimum energy needed to remove one electron from
the metal surface
E = KEelectron+ W
1 eV = 1.6 x10-19 Joule
Work Function
From the photoelectric equation, the minimum energy required by the photon
(to observe the photoelectric effect)must be equal to
the work function
E W=
h f =
The minimum frequency
of the photoelectric
effect
h foIf the photon’s frequency
is less thanthe minimum frequency
Then photoelectric effect cannot occurred
Photoelectric Effect
E = KEelectron+ W
KEelectron = E - Wh f h fo
For Photoelectric to occur:
• Photon’s frequency must be larger than the cut-off frequency.
• Photon’s Energy must be larger than the work function of the
metal.
f > fo
E > W
Examples (UN)
Perhatikan pernyataan berikut!
(1) Elektron dapat keluar dari logam saat permukaan logam
disinari gelombang electromagnetik.
(2) Lepas tidaknya electron dari logam ditentukan oleh frekuensi
cahaya yang datang.
(3) Fungsi kerja untuk setiap logam selalu sama.
Pernyataan yang benar berkaitan dengan efek fotolistrik adalah...
Examples (UN)
Keluarnya elektron dari logam karena radiasi gelombang
elektromagnetik disebut sebagai ....
A. Efek Compton
B. Efek fotolistrik
C. Foton terhambur
D. Fungsi kerja
E. Frekuensi ambang
Examples (UN)
Pernyataan-pernyataan berikut ini berkaitan dengan efek foto listrik:
(1) Efek foto listrik terjadi bila energi foton yang datang pada permukaan
logam lebih besar dari fungsi kerjanya
(2) Kecepatan lepasnya elektron dari permukaan logam bergantung pada
intensitas cahaya yang diterimanya
(3) Banyaknya elektron yang lepas dari permukaan logam bergantung
frekuensi cahaya yang menyinarinya
Pernyataan yang benar adalah ....
Examples (UN)
R
Examples (UN)
Grafik di samping menginformasikanenergi kinetik maksimum elektronyang disebabkan dari logam 1, 2, 3, 4 dan 5 yang disinari cahaya. Frekuensi ambang terbesar adalah ....
5
f
Examples (UN)
1Frekuensi ambang terkecil adalah ....
Compton Effect
Compton effect was first observed by Arthur Compton in 1923.
And this discovery led to his award of the 1927 Nobel Prize in Physics.
The discovery is important because it demonstrates that light cannot be explained purely as a wave phenomenon.
Compton Effect
Foton yang menumbuk electron
akan kehilangan sebagian energinya.
Sebelum Tumbukan Setelah Tumbukan
E E’
h f h f'
>>
Frekuensi
berbandingterbalikdengan
panjanggelombang
Panjanggelombangnya (λ)
bertambah
λ λ’<
Compton Effect
Efek Compton adalah terhamburnya foton setelah ditumbukkan pada
elektron.
momentum
p=
hλ
λ' = wavelength of photon after collision
m = mass of scattered electron
h = Planck’s Constant (6.63 x 10-34 J.s)
ϴ = angle of scattering
De Broglie Wavelength
Example (UN)
Examples (UN)
Panjang gelombang foton setelah menumbuk elektron semakin
besar. Peristiwa tersebut akan mengakibatkan ....
A. Energi foton berkurang
B. Energi foton bertambah
C. Kecepatan gerak foton berkurang
D. Kecepatan gerak foton bertambah
E. Energi sistem akan berubah
Examples (UN)
Jika suatu foton menabrak elektron sehingga terjadi efek
Compton, peristiwa yang tidak terjadi yaitu ....
A. Panjang gelombang foton bertambah
B. Energi foton berkurang
C. Berlaku hukum kekekalan energi
D. Elektron akan terpental dengan energi tertentu
E. Energi sistem berkurang setelah tumbukan