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JEE Main 201412 AprilOnline
Exam
JEE Main
Year
2014
Date
12 April
Mode
Online
Subject
Physics
Chapter
Dual Nature of Matter

JEE Main 2014 · 12 April · Online · Physics · Dual Nature of Matter

For LED's to emit light in visible region of electromagnetic light,...

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

Options

  1. A0.1eV0.1 \mathrm{eV} to 0.4eV0.4 \mathrm{eV}
  2. B0.5eV0.5 \mathrm{eV} to 0.8eV0.8 \mathrm{eV}
  3. C0.9eV0.9 \mathrm{eV} to 1.6eV1.6 \mathrm{eV}
  4. D1.7eV1.7 \mathrm{eV} to 3.0eV3.0 \mathrm{eV}

Correct answer

D. 1.7eV1.7 \mathrm{eV} to 3.0eV3.0 \mathrm{eV}

Step-by-step solution

Energy band gap range is given by, Eg=hcλ\mathrm{E}_{\mathrm{g}}=\frac{\mathrm{hc}}{\lambda}For visible regionλ=(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 \times10^{-7} \sim 7 \times10^{-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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