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The threshold frequency for photoelectric effect on sodium corresponds to a wavelength of 5000 Å. Its work function is:

1. 4 × 10⁻¹⁹ J
2. 1 J
3. 2 × 10⁻¹⁹ J
4. 3 × 10⁻¹⁹ J

Correct answer: 4 × 10⁻¹⁹ J

Solution

The work function (ϕ) is calculated using the formula ϕ = hν = hc/λ. Substituting h = 6.63 × 10⁻³⁴ J·s, c = 3 × 10⁸ m/s, and λ = 5000 Å = 5 × 10⁻⁷ m, we get ϕ = (6.63 × 10⁻³⁴ × 3 × 10⁸) / (5 × 10⁻⁷) = 4 × 10⁻¹⁹ J.

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