[ف.نووي]

How much electromagnetic energy is contained in each cubic meter near the Earth’s surface if the intensity of sunlight under clear skies is 1000 W/m2?
a. 3.3  10–6 J b. 3.3 J c. 0.003 J
d. 10–4 J e. 3.0  105 J

This energy is contained in a cylindrical volume of unit area and height h,
where h = c∆t. Light travels with speed c,
so it travels a distance of h = c∆t in a time interval ∆t.
If we set h = 1 m,
then ∆t = (1/3)*10-8 s.
So E = (S/(3*108 s))(1 m2) is the energy that is contained in a cubic meter.
E = ((1000 W/m2)/(3*108 s))(1 m2) = 3.33*10-6 J.
.