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# A photodetector used to detect the wavelength of 1700 nm, has energy gap of about

$\begin {array} {1 1} (a)\;0.073\: eV & \quad (b)\;1.2\: eV \\ (c)\;7.3 \: eV & \quad (d)\;0.73\: eV \end {array}$

Energy = $hc/\lambda$
$= 6.6 \times 10^{-34} \times 3 \times 10^8 /(1700 \times 10^{-9} \times 1.6 \times 10^{-19} ) eV$
$= 0.73 eV$