Modern Physics

Modern Physics

1. The Electron

   • Thermionic emission
     • CRT
       • Catode rays -deflected inelectric and magnetic fields
       • TV, CRO (EEG, ECG)
       • W= QV (Ep lost = Ek gained)
     • Current and Intensity are directly proportional
   • Photoelectric effect
     • light of suitable frequecy
       • zinc and GLE,photocell
         • plank ( E= hf)
           • Einsteins photelectric law hf = hfo - Ek
         • sensors (automatic doors, burglar alarm
       • The brighter the light, the greater the current
         • current is directly proportional to intensity
         • Work function, threhold frequency
   • X-rays
     • Rontgen
       • Inverse of photoelectric effect
     • X-ray tube
       • high velocity electrons collide with metal target - tungsten
         • W QV, E= hf
     • High frequency electromagnetic radiation
     • In medicine - take photo, destroy cancer cells
   • Stoney - named
     • Millikan - charge
       • eV or Joules

2. Radioactivity (radioactive decay) - Bequerel (1896)

   • Rutherford - gold foil
     • Bohr model
       • Emission spectrum
     • Atom - atomic number, mass number, isotope
   • Spontanious isintegration -alpha, beta, gamma
     • Ionisation - GM tube
       • burns, cancer, genetic defects
         • Depends on: type of radiation, activity, duration of exposure, part of body
     • Alpha - A down 2, Z down 4
     • Beta - A up one, Z same
     • Half life , Law of radioactive decay (exam edge p. 200/201)
     • Activity - no. of disintegrations pre second (Bq)

3. Nuclear energy

   • Fission (U, Pu)
     • Large nucleus to 2 smaller
       • U235 + n1 - Ba144 + Kr90 + 2n1
         • Reactor: fuel, controlrods, moderator, coolant, shielding
     • chain reaction
   • Fusion
     • 2 small nuclei to one large
       • High temperatures needed to overcome electrostatic forces