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) (1 W = 1 Js^(-1))`
i.e., Energy emitted per sec = 600 J
Energy of one photon, `E = hv = h (c)/(lamda)`
`= (6.626 xx 10^(-34) Js xx 3 xx 10^(8) ms^(-1))/(313.3 xx 10^(-9) m)`
`= 6.344 xx 10^(-19) J`
`:.` Photons emitted per sec `= (600)/(6.344 xx 10^(-19))`
`~= 1 xx 10^(21)`