Question

A 100-watt lightbulb radiates energy at a rate of 100 J/s (The watt, a unit of power, or energy over time, is defined as 1 J/s). If all of the light emitted has a wavelength of 500nm, how many photons are emitted per second? (Assume three significant figures in this calculation.)

Answer 1

E of 1 photon = hc/wavelength
E of 1 photon x # photons = 100 J

Answer 2

2.52*10^-18??? is what I got

Answer 3

never mind it tells me that it is not right. I don't know what I am doing wrong. (6.626*10^-34)(3.00*10^8)/ (500*10^-9)= 3.98*10^-19 so 100/ 3.98*10^-19= 2.52*10^-18

Answer 4

Thanks for showing your work.
I think your error is in the last step. If I divide 100/4E-19 I get an answer like 25E+19 or 2.5E20 Check that out.