Average wavelength of light emitted by a bulb with metal filament is 120nm. calculate the number of photons emitted by such bulb with 20W in one hour.
This is related to Planck constant. The energy(E) generate by emitting a photon with wavelength `lambda` and velocity c in one second is given by;
E = `(hc)/lambda` where h is the Planck constant.
c = velocity of light = `3xx10^8m/s`
`h = 6.6xx10^(-34)`
`E = (6.6xx10^(-34)xx3xx10^8)/(120xx10^(-9))`
`E = 1.65xx10^(-18)J`
Energy consumed by bulb in one hour `= 20xx3600 J`
Number of photons emittedper hour
So `4.4xx10^22` photons will be emitted in one hour.