A light wave has a wavelength of 420nm, calculate the energy of this wave in joules.

E = hfE = energyh = planck's constant = 6.63 x 10^-34f = wave frequency
c = fλf = c/λ
E = hc/λ
c = 3.0 x 10⁸ The speed of light which in this case is the speed of the wave.λ = 420 x 10^-9 As 1nm = 1 x 10^-9m
E = ((6.63 x 10^-34)x(3.0 x 10⁸))/(420 x 10^-9)E = 4.74 x 10^-19J leaving the answer as this is in Joules already.