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A hypothetical photoelectric experiment uses the same monochromatic…

Question

A hypothetical photoelectric experiment uses the same monochromatic light on a metal in two separate runs but the data are reported via stopping potentials only. When 400 nm light is used the stopping potential is 2.10 V, and when 620 nm light is used the stopping potential is 1.00 V. Assuming both data points obey the photoelectric equation with a single work function, determine the work function of the metal in eV.

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Step-by-step solution

Photoelectric: eVs = hc/lambda - phi. Subtracting the two equations eliminates phi:
Vs1 - Vs2 = hc(1/lambda1 - 1/lambda2).
hc = (2.10 - 1.00)/(1/400 - 1/620) = 1.10/(0.0025 - 0.0016129) = 1240 eV·nm.
Then phi = hc/lambda1 - Vs1 = 1240/400 - 2.10 = 3.10 - 2.10 = 1.00 eV.

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