# Video: Calculating the Photon Flux of an Electromagnetic Oscillation

Ed Burdette

An AM radio transmitter radiates 5.00 × 10³ W of electromagnetic radiation at a frequency of 7.60 × 10³ Hz. How many photons per second does the transmitter emit?

02:29

### Video Transcript

An AM radio transmitter radiates 5.00 times 10 to the third watts of electromagnetic radiation at a frequency of 7.60 times 10 to the third hertz. How many photons per second does the transmitter emit?

Weβre told the transmitter gives off 5.00 times 10 to the third watts of power; weβll call this value π. Weβre also told the radiation has a frequency of 7.60 times 10 to the third hertz; weβll call this value π. We want to solve for the number of photons per second emitted by the transmitter, what weβll call capital π.

In this example then, we have a radio transmitter giving off radiation with a power π at a frequency π. To start on our solution, we can recall the relationship for the energy of a photon. The energy πΈ of an individual photon is equal to Planckβs constant β times the frequency of that photon π.

In this exercise, weβll assume that β is equal to exactly 6.626 times 10 to the negative 34th joule seconds. So the energy of a single photon emitted by this radio transmitter equals β times the frequency π. If we also recall that power π is defined as energy per unit time, we can also write that π, the power radiated by the transmitter, equals πΈ, the energy of a single photon, times π, the number of photons per second, which also equals β times π times π per one second.

Since π equals βππ in one second, we can rearrange and say that π equals the power times the time interval, one second, divided by Planckβs constant times π. Weβre now ready to plug in for π, β, and π. With those values entered in, when we calculate this fraction, we find itβs equal to 9.93 times 10 to the 32 power. Thatβs the number of photons emitted by this transmitter every second.