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If the threshold wavelength for a certain metal is 2000 Å, then the work-function of the metal is

1. 6.2 J
2. 6.2 eV
3. 6.2 MeV
4. 6.2 keV

Correct answer: 6.2 eV

Solution

The work function (ϕ) is given by ϕ = hc/λ, where h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s, and λ = 2000 Å = 2 × 10⁻⁷ m. Substituting these values, ϕ = (6.63 × 10⁻³⁴ × 3 × 10⁸) / (2 × 10⁻⁷) = 9.945 × 10⁻¹⁹ J. Converting to eV (1 eV = 1.6 × 10⁻¹⁹ J), ϕ ≈ 6.2 eV.

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