If 10% of the energy supplied to an incandescent light bulb is radiated as visible light, how many visible light photons are emitted by 200watt bulb? Assume wavelength of all visible photons to be 5000Å. Given `h=6.6xx10^(-34)Js`.

Explanation

Here, `lambda=5000Å=5xx10^-7m`,
Energy of photon,
`E=(hc)/lambda=((6.63xx10^(-34))xx(3xx10^8))/(5xx10^-7)`
`=3.96xx10^(-19)J`
A 200 W bulb supplies 200j of energy per second. Energy emitted by lamp per second as visible light, `E_1=200xx10/100=20Js^-1`
Number of photons emitted per second as visible light
`N=(E_1)/E=20/(3.96xx10^(-19))=5.05xx10^(19)`