A 600 W mercury lamp emits monochromatic radiation of wave length 313.3 nm. How many photons are emitted from the lamp per second ? (`h = 6.626 xx 10^(-34) Js`, velocity of light `= 3xx 10^(8) ms^(-1)`)

Options

A. `1 xx 10^(19)`
B. `1 xx 10^(20)`
C. `1 xx 10^(21)`
D. `1 xx 10^(23)`

Answer

C

Explanation

`600 W = 600 J s^(-1)`
`:.` Energy emitted per second = 600 J
Energy of one photon `= (hc)/(lambda)`
`= (6.626 xx 10^(-34) Js xx 10^(8) ms^(-1))/(313.3 xx 10^(-9) m)`
`= 6.394 xx 10^(-19)`
Photon emiited per second `= (600 J)/(6.344 xx 10^(-9)) = 1 xx 10^(21)`