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JEE Advanced levelSingle correct optionDifficulty 3 of 3ss052

Silicon has a band gap of $1.10 eV$ . Using $h c = 1240 eV nm$ , the longest wavelength of light that can excite an electron across the gap is nearest to

A1127 nm
B1364 nm
C11273 nm
D564 nm

Answer: A

The photon energy must be at least the gap:

λ_{ma x} = \frac{h c}{E _{g}} = \frac{1240 eV nm}{1.10 eV} = 1127 nm

(infrared). Multiplying by

E_{g}

or using

h c

in eV angstrom instead gives the wrong values.

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