How Many Photons Are Emitted Based on Intensity and Photon Energy?

[Nopollution]

Dear all,

I have the next question: if we consider the classical definition of electromagnetic intensity it is given by [energy]/[time x surface^2]. At the same time intensity is related to the number of photons of the em radiation. So my question: given for example an intensity of 5W/[sec x cm^2] at energy Ep, how many photons at the same energy are emitted?

Thanks,
Nop

 

[Hootenanny]

Depends on the frequency of the photons. Planck's relationship will give you the energy of a single photon, divide the power by the energy of a single photon to obtain the number of photons passing through the unit area per second.

 

[kyle8921]

parat

Dear Nopparat,

Thank you for your question. Intensity is a measure of the amount of energy per unit time and unit area that is being transmitted by electromagnetic radiation. It is typically measured in units of watts per square centimeter (W/cm^2). This definition applies to all forms of electromagnetic radiation, including visible light, radio waves, and X-rays.

To answer your question, the number of photons emitted at a specific energy (Ep) can be calculated by dividing the intensity (5W/[sec x cm^2]) by the energy of each photon (Ep). This will give you the number of photons emitted per second per square centimeter at that specific energy. For example, if Ep is equal to 1 electronvolt (eV), then there would be 5 x 10^17 photons emitted per second per square centimeter at that energy.

It is important to note that the number of photons emitted may vary depending on the specific source and conditions of the radiation. Additionally, the classical definition of intensity may not always accurately capture the behavior of photons in certain situations, such as when dealing with quantum effects. However, for most practical purposes, this definition of intensity is a useful and accepted measure of electromagnetic radiation.

I hope this helps to clarify the relationship between intensity and the number of photons emitted. Please let me know if you have any further questions.

Best,