Question

The given graph shows the variation of photo-electric current $\left(I\right)$ versus applied voltage $\left(V\right)$ for two different photosensitive materials and for two different intensities of the incident radiation. Identify the pairs of curves that correspond to different materials but same intensity of incident radiation.

Answer 1

Since curve 1 and curve 2 have the same cutoff value, they belong to the same material. Similarly, curve 3 and curve 4 also have the same cutoff voltage, so they also belong to the same material. At V=0, the curves 1 and 3, and 2 and 4 move together, therefore, curves 1 and 3 and curves 2 and 4 correspond to different materials but same intensity of incident radiation.