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  4. If the work function of a photometal is 6.875eV, its threshold wavelength will be (Take text c=3× 108m/s)

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Q. If the work function of a photometal is 6.875eV, its threshold wavelength will be $ (Take\text{ }c=3\times {{10}^{8}}m/s) $

BVP MedicalBVP Medical 2007

Solution:

The minimum energy required for the emission of photoelectron from a metal is called work function of that metal, $ W=\frac{hc}{\lambda } $ where h is Plancks constant, c is speed of light, $ \lambda $ is wavelength. $ \Rightarrow $ $ \lambda =\frac{hc}{W} $ $ =\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{6.825\times 1.6\times {{10}^{-19}}} $ $ =1.8\times {{10}^{-7}} $ $ =1800\times {{10}^{-10}}m $ $ =1800\overset{\text{o}}{\mathop{\text{A}}}\, $