If 5% of the energy supplied to an incandescent light bulb is radiated as visible light, how may visible light photons are emitted by a 100W bulb? Assume the average wavelength of all visible photons to be `5600Å`. Given `h=6.25xx10^(-34)Js`.

Explanation

Here `lamda=5600Å=5600xx10^(-10)m,h=6.625xx10^(-34)Js`
Energy of photon,
`E=(hc)/(lamda)=(6.625xx10^(-34))/(5600xx10^(-10))=3.549xx10^(-19)J`
Visible energy radiated by the bulb per second
`=(5)/(100)xx100=5J`
`:.` Number of visible photons emitted per second
`=(5)/(3.549xx10^(-19))=1.41xx10^(-19)`