The wavelength of a certain beam of light was .
calculate how much energy this light has.

Λ represents the wavelength, E the energy, h the constant of Planck, and c the celerity of light.
E = hc / λ, in which h = 6.63 * 10^-34 J.s, c = 3*10^8 m/s, and λ = 3.52*10^-7 m
So E = (6.63 * 10^-34 * 3 * 10^8) / 3.52 * 10^-7 
     E = 1.989 * 10^-25 / 3.52 * 10^-7
     E ≈ 5.65 J

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