The electromagnetic theory of light failed to explain:

The work function of aluminium is $4.2 \ eV$. If two photons, each of energy $3.5 \ eV$, strike an electron of aluminium, then the emission of electrons will be:

Assertion : Photoelectric saturation current increases with the increase in frequency of incident light.
Reason : Energy of incident photons increases with increase in frequency and as a result photoelectric current increases.

Define the work function of a metal and write its unit.

Which graph represents the relationship between the intensity of incident light on a metal plate and the resulting photoelectric current?

The curves $(a), (b), (c)$ and $(d)$ show the variation between the applied potential difference $(V)$ and the photoelectric current $(i)$,at two different intensities of light $(I_1 > I_2)$. In which figure is the correct variation shown?