# The Photoelectric Effect: A Problematic Problem

The maximum energy of photoelectrons emitted from potassium is $$2.1 eV$$ when illuminated by light of wavelength $$3 \times 10^{-7}$$ m and $$0.5 eV$$ when the light wavelength is $$5\times 10^{-7}$$ m. Use these results to obtain values for the minimum energy needed to free an electron from potassium, in $$eV$$.

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