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A metallic surface is illuminated by light of a specific wavelength, and the stopping potential required to halt the emitted photoelectrons is measured to be 6.0 V. When the surface is exposed to light with a wavelength four times longer and intensity reduced to half, the stopping potential decreases to 0.6 V. What are the wavelength of the initial light source and the work function of the metal, respectively? [Use hc/e = 1.24 × 10⁻⁶ J m C⁻¹].

1. 1.72 × 10⁻⁷ m, 1.20 eV
2. 1.72 × 10⁻⁷ m, 5.60 eV
3. 3.78 × 10⁻⁷ m, 5.60 eV
4. 3.78 × 10⁻⁷ m, 1.20 eV

Correct answer: 1.72 × 10⁻⁷ m, 1.20 eV

Solution

Using the photoelectric equation, the stopping potential and wavelength relationship are analyzed. The initial wavelength is calculated as 1.72 × 10⁻⁷ m, and the work function is determined to be 1.20 eV based on the energy difference.

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