Question

In a measurement of quantum efficiency of photosynthesis in green plants, it was found that 10 quanta of red light of wavelength $6850\mathring{A}$ were needed to release one molecule of $O_2$. The average energy storage in this process is $112kcal$ per mol of $O_2$ evolved. What is the energy conversion efficiency in this experiment?
Given: $1cal=4.18J;N_A=6\times {10}^{23};h=6.63\times {10}^{-34}J.s$

• A. $23.5$
• B. $26.9$
• C. $66.34$
• D. $73.1$

Answer 1

The correct option is B $26.9$

$E=\frac{hc}{\lambda }=2.9\times {10}^{-19}J$
Total energy of 10 quanta $\Rightarrow 10\times 2.9\times {10}^{-19}\Rightarrow 29\times {10}^{-19}J$
Energy stored for process $=112$ $kcal$$=\frac{112\times 4.18\times {10}^3}{6\times {10}^{23}}=7.80\times {10}^{-19}J$
$\%$ efficiency $=\frac{7.8\times {10}^{-19}}{29\times {10}^{-19}}\times 100\Rightarrow 26.9\%$