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An LED is constructed from a p-n junction diode using GaAsP. The energy gap is 1.9 eV. The wavelength of light emitted will be equal to:

1. 654 × 10⁻¹¹ m
2. 10.4 × 10⁻⁶ m
3. 654 nm
4. 654 Å

Correct answer: 654 nm

Solution

The wavelength of light emitted can be calculated using the formula λ = hc/E, where h is Planck's constant, c is the speed of light, and E is the energy gap. Substituting the values (h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s, E = 1.9 eV = 1.9 × 1.6 × 10⁻¹⁹ J), we get λ ≈ 654 nm.

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