Consider beam of electron (each electron with energy $E_0$ ) incident on a metal surface kept in an evaluated chamber. Then

Question

$\begin{array}{1 1} \text{no electrons will be emitted as only photons can emit electrons } \\ \text{electrons can be emitted but all with an energy} E_0 \\ \text{electrons can be emitted with any energy , with a maximum of} E_0 -\phi \\ \text{electrons can be emitted with any energy , with a maximum of} E_0 \end{array}$