If the photoelectric work function of a metal is ' φ ' and the...

According to Einstein's photoelectric equation, the energy of the incident photon is given by $E = h\nu$.

For photoelectric emission to take place, the energy of the incident photon must be greater than or equal to the work function of the metal, i.e., $h\nu \geq \phi$, which implies $\nu \geq \dfrac{\phi}{h}$.

Therefore, there will be no emission of photoelectrons if the energy of the incident photon is less than the work function, which means $h\nu < \phi$, or $\nu < \dfrac{\phi}{h}$.

Answer: $\nu < \dfrac{\phi}{h}$