A) 1.89 eV
B) 2.89 eV
C) 3.89 eV
D) 4.89 Ev
Correct Answer: A
Solution :
From Plancks law, the energy \[(E)\] of a wave of wavelength \[\lambda \] is \[E=\frac{hc}{\lambda }\] where,\[h\]is Plancks constant, c is speed of light, and \[\lambda \]is wavelength. Given, \[h=6.625\times {{10}^{-34}}\,J-s\] \[c=3\times {{10}^{8}}\,m/s,\,\lambda =6560\overset{\text{o}}{\mathop{\text{A}}}\,=6560\times {{10}^{-10}}\,m,\] \[1\,eV=1.6\times {{10}^{-19}}\,J\] \[\therefore \] \[E=\frac{6.625\times {{10}^{-34}}\times 3\times {{10}^{8}}}{6560\times {{10}^{-10}}\times 1.6\times {{10}^{-19}}}eV\] \[\Rightarrow \] \[E=1.89\,eV\]
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