Calculate the number of photons emitted per second by a 10 watt sodium vapor lamp. Assume that 90% of the consumed energy is converted into light. Wavelength of sodium light is 590nm. `h=6.62xx10^(-34)Js`

Options

A. `0.256x10^(18)`
B. `0.267xx10^(19)`
C. `0.267xx10^(20)`
D. `0.267xx10^(17)`

Answer

C

Explanation

Energy of photon, `E=(hc)/(lamda)`
`=(6.63xx10^(-34)xx3xx10^(8))/(590xx10^(-9))`
`=(6.63xx3)/(59)=10^(-18)`
Light energy produced per second `=(90)/(100)xx10`
=9W
Number of photons emitted per sec
`=(9xx59)/(6.63xx3xx10^(-18))=2.67xx10^(-19)`