Question

The number of photons emitted in $10hours$ by a $60W$ sodium lamp ($\lambda =5893\mathring{A}$) will be:

• A. $1.6\times {10}^{24}$
• B. $3.2\times {10}^{24}$
• C. $6.5\times {10}^{24}$
• D. $8\times {10}^{24}$

Answer 1

Answer: (C)

$6.5\times {10}^{24}$

Amount of energy emitted in 10 hours is $=60\times (10\times 60\times 60)J=2160000$ J

Energy of 1 photon = $\frac{hc}{\lambda }=(6.626\times {10}^{-34})\frac{3\times {10}^8}{5893\times {10}^{-10}}=0.0033\times {10}^{-16}$

No. of photons emitted = $\frac{216\times {10}^4}{0.0033\times {10}^{-16}}=65454\times {10}^{20}=6.5\times {10}^{24}$