Module 5 : MODERN PHYSICS
Lecture 24 : PHOTONS
Example 6
  Earth receives 1.4 kW of energy from the sun. If it is assumed that the sunlight consists of monochromatic radiation of wavelength 600 nm, how many photons arrive at the earth every second ?
  Solution
 
If $ \lambda = 600$ nm, the corresponding frequency is $ \nu = c/\lambda = 5\times 10^{14}$ Hz. Thus the number of photons per second is
 
$\displaystyle N = \frac{P}{h\nu} = \frac{1400}{6.63\times 10^{-34}\times 5\times 10^{14}}= 4.21\times 10^{21}$
 

 Back