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