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Q.
The number of photons emitted in $10$ hours by a $60 \,W$ sodium lamp $(\lambda = 5893 \,\mathring{A}$) will be :
Structure of Atom
Solution:
Energy of $1$ photon $=\frac{ hc }{\lambda}$
$=\frac{6.62 \times 10^{-34} \times 3 \times 10^{8}}{5893 \times 10^{-10}}$
$=3.37 \times 10^{-19} J$
Total energy emitted by sodium lamp
$=60\, Watt =60 \,J / sec$
$\therefore $ Number of photon emitted in
$1 \sec =\frac{60}{3.37 \times 10^{-19}}$ and in $10$ hours
Total no. of emitted photons $=\frac{10 \times 3600 \times 60}{3.37 \times 10^{-19}}$
$=6.4 \times 10^{24}$