Question

The intensity of the electromagnetic radiation from the sun reaching the Earth’s upper atmosphere is 1.37 kW/m2 . Assume that the average wavelength for this radiation is 680 nm.

a. Find the number of photons per second that strike a 1 m by 3 m solar panel directly facing the sun on an orbiting satellite.

b. What is the number of photon per second if the panel is tilted 25degrees away from the sun?

Answer 1

Here ,

a) energy falling per second , E = 1370 J/(s .m^2)

Now, energy of each photon = h * c/wavelength

energy of each photon = 6.6265 *10^-31 * 3 *10^8/(680 *10^-9)

energy of each photon = 2.92 *10^-19 J

for the total number of photons = 1370 * 1 * 3/(2.92 *10^-19)

total number of photons = 1.41 *10^22

total number of photons falling each second is 1.41 *10^22

b) for theta = 25 degree

for the total number of photons = 1370 * 1 * 3/(2.92 *10^-19) * cos(25 degree)

total number of photons = 1.31 *10^22 1/s