Effect of intensity of incident light on photoelectric current

What this figure shows. An evacuated glass envelope with a quartz window is shown containing a semi-cylindrical cathode C made of photosensitive material and a rod-shaped anode A along its axis, illuminated from outside by a source S of electromagnetic radiation of adjustable frequency $\nu$ and intensity $I$. The cathode and anode are connected through a potential-divider arrangement PQ fed by a high-tension battery B and a key K, so that plate A can be set to any desired positive or negative potential relative to C; a centre-zero voltmeter V reads this potential difference while a micro-ammeter $\mu A$ in series measures the resulting photocurrent. This single apparatus is the workhorse used to independently study how the photocurrent responds to intensity, …

What this figure shows. A graph with light intensity $I$ plotted along the horizontal axis and photoelectric current plotted along the vertical axis, drawn as a straight line passing through the origin, with a caption noting that the frequency of the light and the accelerating potential of the anode are both held constant throughout. The straight-line, origin-passing shape is the direct graphical statement of the first experimental law of the photoelectric effect: the photocurrent -- and hence the number of photoelectrons ejected per second -- is directly proportional to the intensity of the inciden …