# Physics

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A special kind of light bulb emits monochromatic light of wavelength 630 nm. Electrical energy supplied to it at the rate of 60W, and the bulb is 93% efficient at converting that energy into light energy. How many photons are emitted by the bulb during its life time of 730h?

• Physics -

find the energy per photon (E=hc/Lambda)

find the total energy: 60*730*3600 watts

numberphotons*.93*hc/lambda=60*730*3600

solve for number photons

check my thinking.

• Physics -

The correct answer should be numberphotons*hc/lambda=.93*60*730*3600 because the 93% efficiency applies to the bulb and not the energy per photons.

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