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

Answer

2

Explanation

`P = (nhc)/(lambda)`.
`n = 3 xx 10^(16)`