Dual Nature of Matter

JEE Main level, single correct, medium

83 of 200

Question 83 of 200

For LED's to emit light in visible region of electromagnetic light, it should have energy band gap in the range of:

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Answer: (D) 1.7eV1.7 \mathrm{eV} to 3.0eV3.0 \mathrm{eV}

Energy band gap range is given by,
Eg=hcλ\mathrm{E}_{\mathrm{g}}=\frac{\mathrm{hc}}{\lambda}

For visible region
λ=(4×10−7∼7×10−7)mEg=6.6×10−34×3×1087×10−7=19.8×10−267×10−7=2.8×10−191.6×10−19Eg=1.75eV\begin{aligned} &\lambda=\left(4 \times 10^{-7} \sim 7 \times 10^{-7}\right) \mathrm{m} \\ &\mathrm{E}_{\mathrm{g}}=\frac{6.6 \times 10^{-34} \times 3 \times 10^8}{7 \times 10^{-7}} \\ &=\frac{19.8 \times 10^{-26}}{7 \times 10^{-7}} \\ &=\frac{2.8 \times 10^{-19}}{1.6 \times 10^{-19}} \\ &\mathrm{E}_{\mathrm{g}}=1.75 \mathrm{eV} \end{aligned}

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