Question

Calculate number of photons with a wavelength of 3000pm that provides 1 Joule of energy.

Answer 1

   Photon energy = h n  where h = plank's constant and n is frequency
 let there be N photons..   
   Wave length = c / n    where c is velocity of light 
                       = 3000 * 10^-12 m                  
              1 joule = N h c / n  =>  N =  1 * n / (h * c)

N = 1 * 3000 * 10^-12  / (3 * 10^8 *  6.626 * 10^ -34 ) =  10^17 / 6.626 = 1.509 * 10^16