Conductivity of a photodiode starts changing only if the wavelength of incident light is less than 660 nm. The band gap of photodiode is found to be (X/8)eV. The value of X is: (Given, h = 6.6 × 10⁻³⁴ Js, e = 1.6 × 10⁻¹⁹ C) (a) 11 (b) 13 (c) 15 (d) 21

Answer: (c). Cut-off wavelength gives Eg = (hc)/(λ). Eg = 6.6×10⁻³⁴×3×10⁸660×10⁻⁹ = 3×10⁻¹⁹ J Eg = 3×10⁻¹⁹1.6×10⁻¹⁹ = 1.875 eV = 15/8 eV So X = 15, answer (c).

Conductivity of a photodiode starts changing only if the wavelength… | JEE Main 2024 (1 Feb, Shift 2)

Q27JEE Main 2024 · 1 FEB · SHIFT 2Easy

Special Purpose Diodes

Conductivity of a photodiode starts changing only if the wavelength of incident light is less than $660\text{ nm}$ . The band gap of photodiode is found to be $\left(\frac{\text{X}}{8}\right)\text{eV}$ . The value of $\text{X}$ is:

(Given, $\text{h} = 6.6 \times 10^{-34}\text{ Js}, \text{e} = 1.6 \times 10^{-19}\text{ C}$ )

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Answer: (c)

Cut-off wavelength gives $E_g = \dfrac{hc}{\lambda}$ .
$E_g = \dfrac{6.6\times10^{-34}\times3\times10^{8}}{660\times10^{-9}} = 3\times10^{-19}$ J
$E_g = \dfrac{3\times10^{-19}}{1.6\times10^{-19}} = 1.875\ \text{eV} = \dfrac{15}{8}$ eV
So $X = 15$ , answer (c).

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