A student investigates the photoelectric effect and obtains experimental data for the maximum kinetic energy EkE_{\text{k}}Ek of photoelectrons emitted from a metal surface at different frequencies f f\,f of incident radiation. The results are shown on the graph below.
Which option is a correct analysis of the relationship shown in the graph?
EkE_{\text{k}}Ek is directly proportional to fff because the graph is a straight line with a constant gradient.
EkE_{\text{k}}Ek has a linear relationship with fff but is not directly proportional to it, and the threshold frequency is 2.5×1014 Hz2.5 \times 10^{14}\text{ Hz}2.5×1014 Hz.
EkE_{\text{k}}Ek is inversely proportional to fff because the line of best fit does not pass through the origin.
EkE_{\text{k}}Ek is non-linearly related to fff because the ratio Ekf\frac{E_{\text{k}}}{f}fEk varies across the plotted range.
