**Question 2.8: What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of ****energy?**

**Question 2.8: What is the number of photons of light with a wavelength of 4000 pm that provide 1 J of ****energy?**

**Ans 2.8:** Energy (E) of a photon = hν

Energy (E_{n}) of ‘n’ photons = nhν

ν = c/Λ

n = E_{n}Λ /hc

Where, λ = wavelength of light = 4000 pm = 4000 ×10^{–12} m

c = velocity of light in vacuum = 3 × 10^{8} m/s

h = Planck’s constant = 6.626 × 10^{–34} Js

Substituting the values in the given expression of n:

n = (1) × 4000 ×10^{–12} m / 6.626 × 10^{–34} Js × 3 × 10^{8} m/s

n = 2.012 × 10^{16}

Therefore, the number of photons with a wavelength of 4000 pm and energy of 1 J is 2.012 × 10^{16}.

Advertisement