A beam of light falls on a metal surface such that photo-electrons...

The power of the incident light is $P = n h \nu$, where $n$ is the number of photons incident per unit time and $\nu$ is the frequency.

As the power decreases linearly with time, the number of incident photons $n$ also decreases linearly, assuming the frequency $\nu$ remains constant.

The photocurrent $I$ is directly proportional to the number of incident photons per unit time ($I \propto n$). Thus, the photocurrent $I$ decreases linearly with time.

The stopping potential $V$ is given by Einstein's photoelectric equation $e|V| = h\nu - \Phi$, where $\Phi$ is the work function of the metal.

Since the frequency $\nu$ and the work function $\Phi$ are constant, the stopping potential $|V|$ remains constant over time, independent of the light's power.

Therefore, the graph of $I$ versus $t$ is a straight line with a negative slope, and the graph of $|V|$ versus $t$ is a horizontal line.

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