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

Explanation

`lamda = 4000" pm " = 4000 xx 10^(-12) m = 4xx 10^(-9) m`
`E = Nhv = N h(c)/(lamda) :. N = (E xx lamda)/(h xx c) = ((1J) xx (4xx 10^(-9) m))/((6.626 xx 10^(-34) Js) (3.0 xx 10^(8) ms^(-1))) = 2.012 xx 10^(16)` photons