$word_{count}$: 200

Einstein's equation: $KE_{max}$ = hv - phi = h(v - $v_0$). phi = $hv_0$ = work function (minimum energy for ejection). Below $v_0$: no electrons ejected regardless of intensity. Above $v_0$: KE increases linearly with v. Number of electrons proportional to intensity (not frequency). Stopping potential: $eV_0$ = $KE_{max}$. Graph of KE vs v: straight line, slope = h, x-intercept = $v_0$, y-intercept = -phi. Energy shortcut: E(eV) = 1240/lambda(nm). Threshold wavelength: $lambda_0$ = 1240/phi(eV). Key distinctions: frequency determines KE (energy per photon), intensity determines current (number of photons per second). Photoelectric effect proved the particle nature of light. It cannot be explained by wave theory because: (1) there's a threshold frequency, (2) KE depends on frequency not intensity, (3) emission is instantaneous. Compton scattering provided further evidence of photon momentum.