The figure shows the variation of photo current (i) and anode potential (V) for a photo sensitive surface for three different radiations. Let I_a, I_b and I_c be the intensities and f_a, f_b and f_c be the frequencies for the curves A, B and C respectively, then

From the graph, we note that the saturation current is same for curves b and c but different for curve a. Therefore, intensities of b and c will be equal but different from that of a i.e. $I_a$​=$I_b$ but $I_b=I_c$. As stopping potential is same for curves a and b, hence ${\nu }_a$=${\nu }_b$