Monochromatic radiation of wavelength 640.2 nmY from a neon lamp irradiates photosensitive material made of calcium or tongusten. The stopping votage is measured to be 0.54V. The source is replaced by an iron source and its 427.2 nm line irradiates the same photo cell. Predict the new stopping voltage.

Explanation

Work function of the photoelectric cell,
`W_(0) = (hc)/(lamda) - eV_(0)`
`= ((6.626 xx 10^(-34) xx 3 xx 10^(8))/(640.2 xx 10^(-9)) - 1.6 xx 10^(-19) xx 0.54)`
`= 1.40 eV`
In the second case, `lamda` = 427.2 nm
`:. V_(0) = (1)/(e) ((hc)/(lamda) - W_(0)) = (1)/(1.6 xx 10^(-19)) xx ((6.626 xx 10^(-34) xx 3 xx 10^(8))/(427.2 xx 10^(-9)) - 2.24 xx 10^(-19))`
= 1.51 V