Question

A 600 W mercury lamp emits monochromatic radiation of wavelength 331.3 nm. How many photons are emitted from the lamp per second?
( $h=6.626\times 10^{-34}$ Js; velocity of light $=3\times 10^{8}m{s}^{-1}$ )

• A. $1\times 10^{21}$
• B. $1\times 10^{23}$
• C. $1\times 10^{22}$
• D. $1\times 10^{20}$

Answer 1

Answer: (A)

Here, power $=600$ W
$\lambda =331.3nm=331.3\times 10^{-9}m$
$h=6.626\times 10^{-34}Js$
$c=3\times 10^{8}m{s}^{-1}$
$t=1sec$
$Power=\frac{Energy}{Time}=\frac{nhc}{\lambda \times t}$
$600=\frac{n\times 6.626\times 10^{-34}\times 3\times 10^8}{331.3\times 10^{-9}\times 1}$
$n=\frac{600\times 331.3\times 10^{-9}}{6.626\times 10^{-34}\times 3\times 10^8}$
$=1\times 10^{21}$