Photon's emmited by a 100w bulb.

[Seda]

This is my question verbatim:

"If 5% of the power of a 100w bulb is radiated in the visible spectrum, how many visible photons are radiated per second?"

My work:Obviously, 5% of 100w is 5w, or obviously, 5 J/s.So the bulb is emanating 5 J of visble light per second.Now, I could easily solve this if I knew exactly what frequency (or wavelength) of visible light this bulb was emanating, but I don't. If I knew the frequency, I could simply use

E (per photon) = hf where h is Planck's constant.

And then simply do 5 J / E (per photon) = # of photons.But I'm not given a frequency, and wavelength, or even what type of bulb this is.

Any ideas?

Mabye I should use the lowest and highest wavelengths of visible light and just give a range of photons...

 

[Redbelly98]

For a problem of this sort, just using the wavelength in the middle of the visible range (as an "average" visible photon) is probably sufficient.

 

[baba89]

I would suggest approaching this problem by using the concept of energy conservation. We know that the total energy emitted by the bulb is 5 J/s, and this energy is distributed among all the photons emitted. Therefore, we can use the equation E = hc/λ, where h is Planck's constant, c is the speed of light, and λ is the wavelength, to calculate the average energy per photon.

Once we have the average energy per photon, we can use the fact that the power of a light source is equal to the number of photons emitted per unit time multiplied by the average energy per photon. So, we can rearrange the equation to find the number of photons emitted per second, which would give us the answer to the question.

In order to find the average energy per photon, we can use the fact that the visible spectrum ranges from approximately 400-700 nm in wavelength. We can take the average of these two values (550 nm) and use it in the equation. This will give us an approximate value for the average energy per photon.

It is important to note that this calculation will give us an average number of photons emitted per second. In reality, the number of photons emitted per second will vary depending on the specific wavelength of each photon. However, this approach will give us a reasonable estimate of the number of photons emitted in the visible spectrum from a 100w bulb.

In summary, to answer the question, we would need to use the concept of energy conservation and the equation E = hc/λ to calculate the average energy per photon. Then, we can use the relationship between power, number of photons, and energy per photon to estimate the number of visible photons emitted per second from a 100w bulb.