A sodium incandescent bulb emits 589 nm wavelength light at 60watts. calculate the number of photons emitted by the bulb.

Energy of one photon = E = hν =\(frac{hc}{lambda }=6.623times {{10}^{-34}}times 3times {{10}^{8}}times frac{1}{589times {{10}^{-9}}}=3.37times {{10}^{-19}}J\)

Energy released by the bulb = 60watt = 60J/s

Number of photons =\(frac{Energy,,,,released}{Energy,,of,,one,,photon}=frac{60}{3.37times {{10}^{-19}}}\)= 1.78×1020/s

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