The energy flux of sunlight reaching the surface of the earth is 1.388 × 103 W/m2 . How many photons (nearly) per square metre are incident on the Earth per second? Assume that the photons in the sunlight have an average wavelength of 550 nm.
Given: The energy flux of sunlight is 1.388 × 10 3 W / m 2 and the average wavelength of photons is 550 nm .
The power of sunlight per square meter equals to the energy flux of the sunlight.
The energy of photon is given as,
E = h c λ (1)
The energy of photons is also given as,
E = P n (2)
From equation (1) and (2) it can be written as,
n = P λ h c
Where, Planck’s constant is h , the speed of light is c and the wavelength is λ , the power of the photon is P and the numbers of photons are n .
By substituting the given values in the above equation, we get
n = 1.388 × 10 3 × 550 × 10 − 9 6.626 × 10 − 34 × 3 × 10 8 = 3.84 × 10 21 photons / ( m 2 s )
Thus, the number of photons per square metre incident on the earth per second is 3.84 × 10 21 .
Given: The energy flux of sunlight is
The power of sunlight per square meter equals to the energy flux of the sunlight.
The energy of photon is given as,
The energy of photons is also given as,
From equation (1) and (2) it can be written as,
Where, Planck’s constant is
By substituting the given values in the above equation, we get
Thus, the number of photons per square metre incident on the earth per second is
