Quantum Phenomena

Quantum Phenomena

1. Photoelectricity

   • Electrons emitted from surface of metals when hit by EM Radiation
     • Emitted proportional to intensity after TFreq.
   • Threshold Freq.
     • Min freq needed for photoelectric effect- changes for diff metals
       • f= WF/h
     • wavelength must be less than c/threshold freW
   • Wave Theory proven wrong
     • Emission would occur with any frequency of waves
     • The time taken for the electrons to be emitted would change with insensity
       • But always immediate and emission changes with freq. = photons
   • Einstien
     • energy of photon= hf
     • Electron emitted if energy from photon exceeds the Work Function of the metal
       • E (max)= hf- WF
         • max energy of emitted electron
       • energy from photon= energy of emitted electron
         • Extra energy used as kinetic energy of electron

2. Vacuum Photocell

   • The electrons emitted from the photocathode when light hits it complete the circuit to the anode
   • Photoelectric current proportional to the light intensity

3. Energy Levels

   • Excitation
     • Atoms can absorb energy and not be ionised
       • Needs more energy for ionisation than excitation
     • Energy values when atom absorbs energy= excitation energies
     • Atom moves up an energy level(s) with excitation energy
       • Ionisation level=0 other excitation levels= -
     • Electron can absorb photon and move up every levels equal to the energy of the photon
   • Electrons
     • Closer to nucleus=less energy
     • Lowest energy level= ground state
       • Any above that= excited state
   • De-Excitation
     • Vacancy in shell from excitation leaves atom unstable
     • Another electron moves back into shell, emitting a photon
     • energy of photon= energy of 1st level-energy of 2nd
   • Flurescence
     • Electrons absorb UV photons and emit photons when they de-excite

4. Spectra

   • Wavelengths of light emitted/ absorbed by electrons correspond to the pattern of spectra- no spectrum is the same because the energy levels are different in every atom

5. Wave Particle Duality