A) \[8000\text{ }\overset{o}{\mathop{\text{A}}}\,\]
B) \[7000\text{ }\overset{o}{\mathop{\text{A}}}\,\]
C) \[\text{1472 }\overset{o}{\mathop{\text{A}}}\,\]
D) \[\text{2950 }\overset{o}{\mathop{\text{A}}}\,\]
Correct Answer: D
Solution :
Suppose the cut-off wavelength is represented by\[{{\lambda }_{0}}\] So, \[\frac{hc}{{{\lambda }_{0}}}=\]work function \[={{W}_{0}}\] \[\frac{hc}{{{\lambda }_{0}}}=4.2\times 1.6\times {{10}^{-19}}\] \[{{\lambda }_{0}}=\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{4.2\times 1.6\times {{10}^{-19}}}\] \[=2946\times {{10}^{-10}}m\approx 2950\,\overset{o}{\mathop{\text{A}}}\,\]
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