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 $=3\times 10^{8 \, }ms^{- 1}$ )

• 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
$\lambda =331.3 \, nm=331.3\times 10^{- 9 \, }m$
$h=6.626\times 10^{- 34 \, }Js$
$c=3\times 10^{8 \, }ms^{- 1}$
$t=1 \, sec$
$Power=\frac{E n e r g y}{T i m e}=\frac{n h c}{\lambda \times t}$
$600=\frac{n \times 6.626 \times 1 0^{- 34} \times 3 \times 1 0^{8}}{331.3 \times 1 0^{- 9} \times 1}$
$n=\frac{600 \times 331.3 \times 1 0^{- 9}}{6.626 \times 1 0^{- 34} \times 3 \times 1 0^{8}}$
$=1\times 10^{21}$