Sodium vapor lamps, used for public lighting, emit yellow light of wavelength 589 nm. How much energy is emitted by (a) an excited sodium atom when it generates a photon; (b) 5.00 mg of sodium atoms emitting light at this wavelength; (c) 1.00 mol of sodium atoms emitting light at this wavelength?
The answer for this question is below. My question is why is it lambda -1? Why is that the formula, how would I know?
(a) From c= va and E = hv, we can write E = hc2-1 = (6.626 08 x 10-34 J·s) (2.997 92 x 108) (589 x 10-ºm) = 3.37 x 10-19 J -1 (b) E 5.00 x 10-3 g Na (6.022 x 1023 atoms · moll) 22.99 g.mol-'Na (3.37 x 10-\ J atom-') = 44.1 J (c) E=(6.022 x 1023 atoms · mol-')(3.37 x 10-19 J • atom-') = 2.03 x 10J or 203 kJ