Given:

Wavelength, λ = 4000 pm

Energy, E = 1 J

By Planck’s relation we have,

Energy, E = h×v

But we know v = [c] / [λ]

Where

c = Speed of Light

v= Frequency

λ = Wavelength

So, E = hc /λ

= [[6.626×10^-34] × [3×10⁸]] / [4000×10^-12]

= [1.9878×10^-25] / [4000×10^-12]

= 4.9695×10^-17 J

4.9695×10^-17 J is the Energy of 1 photon

So, 1 J is the energy of X number of photons

X = [1] / [4.9695×10^-17]

X = 2.012×10¹⁶ photons

So, the number of photons which provide 1 J of energy is 2.012×10¹⁶ photons.