Question

Number of photons emitted in $5$ hours by a $50\, W$ 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 $=\frac{h c}{\lambda}$

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

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

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

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