Monochromatic radiation of wave length $640.2 nm$ from a neon lamp irradiates a photo sensitive material made of calcium or tungsten. The stopping voltage is mentioned to be $0.54\;v$ . The source is replaced by an iron source and its $427.2\;nm$ line irradiates the same photo cell . predict the new stopping voltage .

Question

$\begin{array}{1 1} 1.55 \;v \\ 155\;v \\ 15.5 \;v \\ 0. 1555v \end{array}$