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

Explanation

Wavelength of light, `lambda = 4000 p m`
`= 4000 xx 10^(-12) m = 4 xx 10^(-9) m`
Energy of 1 photon,
`E = (hc)/(lambda)`
`h = 6.626 xx 10^(-34) J s, c = 3.0 xx 10^(8) ms^(-1)`
`:. " " E = (6.626 xx 10^(-34) xx 3.0 xx 10^8)/(4 xx 10^(-9))`
`= 4.97 xx 10^(-17) J`
No. of photons providing 1 J of energy
`= (1)/(4.97 xx 10^(-17)) = 2.01 xx 10^(16)` .