Why we study this chapter? Some application in light quantum physics SOLAR CELL TECHNOLOGY
Theory of Light
WAVE Photoelectric Effect
PARTICLE Compton Effect
Light has both wave and particle characteristic
Blackbody Radiation A black-body is any object that can absorb or emit radiation energy
Emissivity (𝑒)
0≤𝑒≤1
Perfect Reflector Reflects all radiation energy it received.
Perfect absorber or emitter 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. The energy of light can be stated as,
𝑓=
E =ℎ𝑓 c __ λ
h = Plank’s Constant (6.63 x 10-34 J.s) f = Photon’s Frequency (Hz)
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) The energy of light can be stated as,
E =ℎ𝑓 _34 = (6.63𝑥10 Js)(15.08x106 Hz) = 100 x
-28 10
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) The energy of single photon can be stated as,
𝑐 E =ℎ = 𝜆
= =
8
(6.63x10-34)
(3𝑥10 ) −9 663𝑥10
(10-34) (3x1015) 3x10-19 J
Photoelectric Effect in 1887 Hertz observed a phenomenon during his experiments which proved the existence of electromagnetic waves characteristic in light. This phenomenon was the emission of electrons from a metal surface when light was incident upon it.
PHOTOELECTRIC EFFECT The emitted electrons are called photoelectrons.
Photoelectric Effect If the wavelength of light is held constant, an increase in light intensity causes an increase in the number of electrons emitted. However, the kinetic energy of the emitted photoelectrons does not change. If the intensity of light is held constant, when the wavelength of light is changed, the number of emitted photoelectrons remains the same, but their kinetic energies change. When a different metal is used, depending on the wavelength of light, sometimes no emission is observed.
Electrons are emitted from the surface almost instantaneously. Explained by Einstein in 1905
Photoelectric Effect Energy of Photon
=
Kinetic Energy of Electron
+
Work Function of Metal
E = KEelectron+ W 1 eV = 1.6 x10-19 Joule
The minimum energy needed to remove one electron from the metal surface
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 If the photon’s frequency is less than the minimum frequency Then photoelectric effect cannot occurred
E = W h f = h fo The minimum frequency of the photoelectric effect
Photoelectric Effect
E = KEelectron+ W Wfo KEelectron = hEf - h 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)
5
Grafik di samping menginformasikan energi kinetik maksimum elektron yang disebabkan dari logam 1, 2, 3, 4 dan 5 yang disinari cahaya. Frekuensi ambang terbesar adalah ....
Examples (UN)
f
1
Frekuensi 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 Sebelum Tumbukan
E hf Foton yang menumbuk electron akan kehilangan sebagian energinya.
Frekuensi berbanding terbalik dengan panjang gelombang
> >
Setelah Tumbukan
E’ h f' Panjang gelombangnya (λ) bertambah
λ
<
λ’
Compton Effect Efek Compton adalah terhamburnya foton setelah ditumbukkan pada elektron.
h λ= p momentum 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
Quantum Physics
Quantum Physics
OVERVIEW • Concept of Photon
• Blackbody Radiation and Planck’s Hypothesis • Photoelectric Effect • Compton Effect
• de Broglie Wa...
