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# The quantum efficiency of photosynthesis measurement in green plants indicated that 8 quanta of red light at $6850{\mathrm{A}}^{\mathrm{o}}$ are required to evolve one molecule of oxygen. The average energy storage in the photo-synthetic process is  evolved. Calculate the energy conversion efficiency in the experiment.

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Solution

## $\lambda =6850{\mathrm{A}}^{\mathrm{o}}=6850×{10}^{-10}\mathrm{m};h=6.63×{10}^{-34}\mathrm{Js}$. We know that :$E=\frac{hc}{\lambda }$Thus, $E=\frac{6.63×{10}^{-34}\mathrm{Js}×3.0×{10}^{8}{\mathrm{ms}}^{-}}{6850×{10}^{-10}\mathrm{m}}$or $E=2.9×{10}^{-19}\mathrm{J}$8 quanta means, $E=8×2.9×{10}^{-19}\mathrm{J}=23.2×{10}^{-19}\mathrm{J}$Average energy stored$\begin{array}{l}=\frac{112\mathrm{kcal}}{\mathrm{mol}}×\frac{4184\mathrm{J}}{1\mathrm{kcal}}\\ ×\frac{1\mathrm{mol}}{6.02×{10}^{23}\mathrm{molecules}}\\ =7.78×{10}^{-19}\mathrm{J}/\mathrm{molecule}\end{array}$$\therefore$ Energy conversion efficiency

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