In the explanation of photoelectric effect, we assume one photon of frequency `nu` collides with an electron and transfers its energy. This leads to the equation for the maximum energy `E_max` of the emitted electron as, `E_max = h nu - phi_0` whare `phi_0` is the work function of the metal . If an electron absorbs two photons (each of frequency `nu`) what will be the maximum energy for the emitted electron ?