Question

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

• A. $1\times {10}^{19}$
• B. $1\times {10}^{20}$
• C. $1\times {10}^{21}$
• D. $1\times {10}^{23}$

Answer 1

The correct option is C $1\times {10}^{21}$

$⟹E=\frac{nhc}{\lambda }⟹n=\frac{E\lambda }{hc}=\frac{600\times 331.3\times {10}^{-9}}{6.626\times {10}^{-34}\times 3\times {10}^8}⟹n=1\times {10}^{21}$