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A bulb lamp emits light of mean waveleng...

A bulb lamp emits light of mean wavelength of `4500A`. The lamp is rated at `150W` and `8%` of the energy appears as emitted light. How many photons are emitted by the lamp per second?

Text Solution

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The energy of photon `=(hc)/(lamda)`
`((6.63xx10^(-34))(3xx10^(8)))/(4500xx10^(-10))`
According to the given problem, power of the lamp is 150W. As `8%` of the light energy is utililzed for emission of light, hence the utilized energy for emission per second given by
Useful power `=150xx(8)/(100)=12W`
`=12Js^(1)`
Therefore, number of photons emitted per second by the lamp
`("Useful power")/("Energy of photon")=(12xx4500xx10^(-10))/((6.63xx10^(34))(3xx10^(8)))`
`=27.17xx10^(18)`
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