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The photoelectric work function for a metal surface is 4.125 eV. The cut off wavelength for this surface is

1. 4125 Å
2. 3000 Å
3. 6000 Å
4. 2062.5 Å

Correct answer: 4125 Å

Solution

The cutoff wavelength is calculated using the formula λ = hc/Φ, where h is Planck's constant, c is the speed of light, and Φ is the work function. Substituting Φ = 4.125 eV (1 eV = 1.6 × 10⁻¹⁹ J), h = 6.63 × 10⁻³⁴ J·s, and c = 3 × 10⁸ m/s, we get λ = 4125 Å.

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