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 for $1$ mole $O_2$ evolved is $112$ kcal.
What is the energy conversion efficiency in this experiment?
[Given: $1cal=4.18J;N_A=6\times 10^{23};h=6.63\times 10^{-34}$ Js]

Answer 1

Answer: 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
$=\frac{112\times 4.18\times 10^3}{6\times 10^{23}}=7.80\times 10^{-19}J$
$\%$ efficiency $=\frac{7.8\times 10^{-19}}{29\times 10^{-19}}\times 100$
$\Rightarrow 26.9\%$