Quantum Theory

Quantum Theory

1. Wave-Particle Duality

   • An object at any temperature can emit electromagnetic radiation
   • Black body: an object that absorb all wavelength on it and reflecting none
   • Spectrum of radiation depends on temperature and properties of the object
   • From Stefan-Boltzmann Law, P=δeAT^4
     • δ= Stefan’s constant = 5.6703 x 10-8 watt/m2 K4 e= emissivity A= radiating area T= temperature

2. De Broglie's Hypothesis

   • De Broglie’s hypothesis: light is considered as particle called photon which has mass and momentum
   • From Einstein’s mass-energy/photoelectric equation, mc^2=hc/λ
     • λ=h/mv

3. Planck's Theory

   • Planck’s theory: describe that waves can exhibit particle-like characteristic and particles can exhibit wave-like characteristic
   • Radiation energy, E=hf
     • h= Planck’s constant   = 6.626 x 10-34 J sf= frequency
   • From f=c/λ ,
     • E=hc/λ
       • c= 3.0 x 10^8 m s-1 λ= wavelength

4. Photoelectric effect

   • From the energy conservation, E=W+Kmax
     • hf=hf0+Kmax
   • When electron absorbed photon energy, it overcome the bounding barrier and release itself from the metal surface, and the accelerated by the electric fields
   • The cut-off potential is corresponding to the maximum kinetic energy of electrons,
     • Kmax=eVs=1/2mvmax^2
   • When monochromatic light fell on the cathode, photons weren’t emitted unless the frequency of light was greater than threshold frequency, f0