Question

If a 60-watt lamp emits monochromatic radiation of wavelength 6625 A, then the number of photons emitted per second by the lamp is:

$[h=6.625\times {10}^{-34}Js]$

• A. $4\times {10}^{21}$
• B. $2\times {10}^{19}$
• C. $4\times {10}^{20}$
• D. $2\times {10}^{20}$

Answer 1

Answer: (D)

$2\times {10}^{20}$

The wavelength of monochromatic radiation $=6625\mathring{A}$

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

$=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{6.623\times {10}^{-10}}$

$=3\times {10}^{-19}Joule$

Photon emitted per second$=\frac{60}{3\times {10}^{19}}$

$=2\times {10}^{20}$

Hence, the correct option is $\text{D}$