Question

Number of photons emitted in $5$ hours by a $50W$ sodium lamp is $\left({\lambda }_{\text{photon }}=5893\mathring{A}\right)$

• A. $7.4\times 10^{20}$
• B. $4.46\times 10^{22}$
• C. $2.7\times 10^{24}$
• D. $5.4\times 10^{23}$

Answer 1

Answer: (C)

Energy of one photon $=\frac{hc}{\lambda }$

$=\frac{6.6\times 10^{-34}\times 3\times 10^8}{5893\times 10^{-10}}J$

$50Watt=50J{s}^{-1}$

Energy emitted by sodium lamp in one second $=50J$

Energy emitted in 5 hours $=50\times 5\times 60\times 60$

Number of photons emitted in 5 hours

$=\frac{\text{ Total energy emitted }}{\text{ Energy of one photon }}$

$=\frac{50\times 5\times 3600\times 5893\times 10^{-10}}{6.6\times 10^{-34}\times 3\times 10^8}$

$=2.678\times 10^{24}$ photons