Govt. Exams
From Einstein's photoelectric equation: KE_max = hf - φ. As frequency increases, maximum kinetic energy increases proportionally. Stopping potential depends on frequency, KE depends on frequency (not intensity), and threshold frequency is directly related to work function.
Activity A = dN/dt = λN, measured in Becquerels (decays per second) or Curies. It represents the decay rate.
In alpha decay, a nucleus emits ⁴₂He. Parent nucleus (A,Z) → Daughter (A-4, Z-2) + Alpha particle (4,2).
The stopping potential is related to maximum kinetic energy by: KE_max = eV_s. For V_s = 2V, KE_max = 2 eV.
Alpha particles (⁴₂He) are helium nuclei containing 2 protons and 2 neutrons. They have low penetrating power but high ionizing power.
In β⁻ decay, a neutron converts to proton, emitting electron and antineutrino: n → p + e⁻ + ν̄ₑ
The radius of nth orbit in hydrogen atom is given by rₙ = n²a₀/Z, where a₀ = 0.53 Å is the Bohr radius and Z is atomic number.
The ionization energy of hydrogen in ground state is 13.6 eV. A photon of exactly 13.6 eV can just ionize the atom with zero kinetic energy of the ejected electron.
For hydrogen-like ions: IE = 13.6 × Z² eV. For He⁺, Z = 2, so IE = 13.6 × 4 = 54.4 eV.
Nuclear forces are strong forces that are attractive at normal nuclear distances (~1 fm) but become repulsive at very short distances (<0.5 fm), creating a potential well. They act between all nucleons (protons and neutrons).
