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In a historical experiment to determine Plank's constant, a metal surface was irradiated with light of different wavelengths. The emitted photoelectron energies were measured by applying a stopping potential. The relevant data for the wavelength ( λ ) of incident light and the corresponding stopping potential (V 0 ) are given below. λ ( μ m) V 0 (Volt) 0.3 0.4 0.5 2.0 1.0 0.4 Given that c = 3 × 10 8 m s –1 and e = 1.6 × 10 –19 C, Planck's constant (in units of J s) found from such an experiment is

1. 6.0 × 10 –34
2. 6.4 × 10 –34
3. 6.6 × 10 –34
4. 6.8 × 10 –34

Correct answer: 6.4 × 10 –34

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