what is the number of photons of light with a wavelength of 4000 pm that provide 1 J of energy ?

Explanation

`lambda=4000pm =4000 xx 10^(-12)m`
`v=c/lambda=(3.0 xx 10^(8))/(4000 xx 10^(-12)) =7.5 xx 10^(16)s^(-1)`
Energy associated with one photon
`E=hv=6.626 xx 10^(-34) xx 7.5 xx 10^(16)`
`=4.97 xx 10^(-17) (h=6.626 xx 10^(-34)Js)`
Hence, number of photons which produce 1 J of energy
`=(1)/(4.97 xx 10^(-17))=2.01 xx 10^(16)`