Question

A special kind of light bulb emits monochromatic light of wavelength 700nm .electrical energy supply to it at the rate of 60w and the bulb is 50% efficient at converting that energy to light energy.how many photons are emitted by the bulb during its life time of 1 day?

Answer 1

Answer:

Total number of photon will be $9.069\times 10^{24}photon$

Explanation:

We have given power P = 60 W

Time t = 1 day = 86400 sec

We know that energy is given by

$E=Pt=60\times 86400=5184000J$

It is given that bulb is only 50% efficient

So energy of bulb $\frac{5184000\times 50}{100}=2592000J$

We have given wavelength of the photon = $700nm=700\times 10^{-9}m$

Energy of photon is given by

$E=\frac{hc}{\lambda }=\frac{6.67\times 10^{-34}\times 3\times 10^8}{700\times 10^{-9}}=2.858\times 10^{-19}J$

We know that number of photon is given by

$n=\frac{total\ energy}{energy\ of\ photon}=\frac{2592000}{2.858\times 10^{-19}}=9.069\times 10^{24}photon$