Monochromatic light of wavelength `667 nm` is produced by a helium neon laser . The power emitted is `9 mW` . The number of photons arriving per second on the average at a target irradiated by this beam is

Options

A. `3 xx 10^(19)`
B. `9xx 10^(17)`
C. `3 xx 10^(16)`
D. `9 xx 10^(15)`

Answer

C

Explanation

No. of photon ` =(E)/(hc//lambda)`
`=(9xx10^(-3)xx 6.67xx10^(-7))/(6.6xx10^(-34)xx 3xx10^(8))`
`=3 xx 10^(16)`