Revise: Modern Physics
Cathode rays, X-rays, Bohr's hydrogen atom and atomic spectra, the photoelectric effect, isotopes, and red shift and Hubble's law.
Eβ = β13.6/nΒ² eV; electrons jump between quantised levels, emitting/absorbing specific photon energies.
n=3 to n=1 releases a 12.09 eV photon.
KEmax = hf β Ο; light behaves as discrete photons, each transferring energy to one electron.
Below the threshold frequency, no electrons are ejected regardless of brightness.
v = Hβd; recession speed rises with distance, evidence for an expanding universe.
A galaxy 300 Mpc away recedes at about 21,000 km/s.
Cathode rays are streams of electrons β their study led to discovering the electron.
CRT televisions fired controlled electron beams at a phosphor screen.
X-rays form when fast electrons decelerate sharply on hitting a target.
Bone absorbs more X-rays than soft tissue, creating image contrast.
Isotopes: same protons, different neutrons β nearly identical chemistry, different nuclear stability.
Carbon-14 decay is used to date ancient organic remains.