Ultraviolet light of wavelength 200 nm is incident on a polished surface of iron (Fe). The work function of the surface is 4.71 eV. What will be its stopping potential? (h = 6.626×10⁻³⁴ J s; 1 eV = 1.6×10⁻¹⁹ J; c = 3×10⁸ m s⁻¹)

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(1) 1.5 V. Given: λ = 200 nm = 2×10⁻⁷ m, work function φ₀ = 4.71 eV. Idea: Einstein's equation eV₀ = (hc)/λ - φ₀. Photon energy: (hc)/λ = (6.626×10⁻³⁴×3×10⁸)/(2×10⁻⁷) = 9.94×10⁻¹⁹ J In eV: (9.94×10⁻¹⁹)/(1.6×10⁻¹⁹) = 6.21 eV Kₘₐₓ = 6.21 - 4.71 = 1.50 eV, so eV₀ = 1.50 eV. So the stopping potential is V₀ = 1.5 V.

Ultraviolet light of wavelength 200 nm is incident on a polished surface of iron (Fe). The work function of the surface is 4.71 eV. What will be its stopping potential? (h = 6.626×10⁻³⁴ J s; 1 eV = 1.6×10⁻¹⁹ J; c = 3×10⁸ m s⁻¹)

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