= Solution
In the <photoelectric effect>, incident light ejects <electrons> from a material when each absorbed <photon> supplies sufficient <energy> to overcome its <work function> $W$. <Conservation of energy> gives the maximum emitted <kinetic energy>,
$$
\boxed{K_{\max}=h\nu-W,\qquad \nu\ge\nu_0=W/h.}
$$
At fixed <frequency> above threshold, increasing light <intensity> primarily increases the electron emission rate; it does not increase $K_{\max}$ in the single-<photon> regime. Emission occurs without the long accumulation delay predicted for weak classical illumination.
Classical <electromagnetism> distributes incident <energy> continuously. By itself, that picture suggests that sufficiently intense or sufficiently long illumination could eject <electrons> at any <frequency>, and that emitted <electron> <energies> should increase with light <intensity>. It does not account for the observed threshold <frequency> and the linear dependence of $K_{\max}$ on <frequency> with slope $h$. Quantized <photon absorption> accounts for all three features.
Back to article page
