Question

One type of sunburn occurs on exposure to UV light of wavelength in the vicinity of 305 nm. How many photons are in 1.15mJ burst of this radiation?

Answer 1

$E=ch/\lambda$ E - photon energy, с - speed of light (3*10⁸m/s), $\lambda$ - wavelength, h - Planck's constant (6,23*10^-34kg*m²/s)

E=3*10⁸m/s*6,23*10^-34kg*m2/s/305*10^-9m=6,12*10^-19J

Whole E=0,00115J

N - photons ammount

N=0,00115J/6,12*10^-19J=1,88*10¹⁵ photons

Answer:1,88*10¹⁵ photons