A) \[8000\overset{o}{\mathop{A}}\,\]
B) \[7000\overset{o}{\mathop{A}}\,\]
C) \[1472\overset{o}{\mathop{A}}\,\]
D) \[2950\overset{o}{\mathop{A}}\,\]
Correct Answer: C
Solution :
Suppose the cut of wavelength by \[\lambda ,\] Then \[\frac{hc}{{{\lambda }_{0}}}=\] work function \[={{W}_{0}}.\] Here work function of metal \[{{W}_{0}}=4.2eV\] \[\therefore \] \[\frac{hc}{{{\lambda }_{0}}}=4.2\times 1.6\times {{10}^{-19}}\] \[(\because \,\,1eV=1.6\times {{10}^{-19}}J)\] \[\Rightarrow \] \[{{\lambda }_{0}}=\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{4.2\times 1.6\times {{10}^{-19}}}\] \[\Rightarrow \] \[{{\lambda }_{0}}=2946\times {{10}^{-10}}m=2950\overset{\text{o}}{\mathop{\text{A}}}\,\]
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