The number of photons emitted per second by a 60W source of monochromatic light of wavelength 663nm is

Options

A. a) 4 times 10^-20`
B. b) `1.5 times 10^20`
C. c) `3 times 10^-20`
D. d) `2 times 10^20`

Answer

D

Explanation

Energy `E=(nhc)/lamda`
`implies 60 times1Js= (n times 6.63 times 10^-34 Js times 3 times 10^8m)/(663 times 10^-9m)`
`therefore n=(60 times 1 times 663 times 10^-9)/(6.63 times 10^-34 times 3 times 10^8)`
`=2 times 10^20`