The value of threshold frequency depends on which of the following factors?

$A$ point source of light is used in an experiment on the photoelectric effect. Which of the following curves best represents the variation of photocurrent $(i)$ with distance $(d)$ of the source from the emitter?

The cathode of a photocell is changed such that the work function changes from $w_1$ to $w_2$ $(w_2 > w_1)$. If the saturation currents before and after the change are $I_1$ and $I_2$ respectively,and all other conditions (such as incident light intensity and frequency) remain unchanged,then (assuming $h
u > w_2$):

Define threshold frequency.

In the given figure,$V$ represents the stopping potential. If $\lambda_1$ and $\lambda_2$ are the wavelengths of the incident light and $|V_2| > |V_1|$,then:

The anode voltage of a photocell is kept fixed. The frequency of the light falling on the cathode is gradually increased. Then the correct graph which shows the variation of photo current $I$ with the frequency $\nu$ of incident light is