Question

Number of photons emitted in 10 hours by 60 W sodium lamp is $(\lambda =5983A^o)$

• A. $6.40\times {10}^{22}$
• B. $6.40\times {10}^{24}$
• C. $4.60\times {10}^{22}$
• D. $4.60\times {10}^{42}$

Answer 1

The correct option is B $6.40\times {10}^{24}$

Energy of photon, $E=\frac{hc}{\lambda }$

$=\frac{(6\cdot 63\times {10}^{-34})(3\times {10}^8)}{5893\times {10}^{-10}}$

$=3\cdot 374\times {10}^{-19}J$

Number of photons emitted per sec.

$=\frac{60}{3\cdot 374\times {10}^{-19}}$

Number of photons emitted in 10 hours

$=\frac{60\times 10\times 3600}{3\cdot 374\times {10}^{-19}}=6.40\times {10}^{24}.$