A) \[6000\,\overset{o}{\mathop{A}}\,\]
B) 4000 nm
C) 6000 nm
D) \[4000\,\overset{o}{\mathop{A}}\,\]
Correct Answer: D
Solution :
| Key Idea Only signals having wavelength less than threshold wavelength will be detected. Energy \[E=hv=h\frac{c}{\lambda }\]\[\Rightarrow \]\[\lambda =\frac{hv}{E}\] Substituting the values of h, c and E in the above equation |
| \[\lambda =\frac{6.6\times {{10}^{-34}}\times 3\times {{10}^{8}}}{2.5\times 1.6\times {{10}^{-19}}}=5000\,\overset{o}{\mathop{A}}\,\] |
| As \[4000\,\overset{o}{\mathop{A}}\,<5000\,\overset{o}{\mathop{A}}\,\] |
| Signal of wavelength \[4000\,\overset{o}{\mathop{A}}\,\] can be detected by the photodiode. |
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