# Is the energy of an electromagnetic wave, in electron volts, an 'average' or a 'peak' value?

Since EM waves oscillate, is the energy given in eV an average or maximum value?

In a related question, can a detector (of whatever sort) 'miss' an EM wave if the amplitude is at a minimum when it goes past the detector?

• With waves we talk about peak or average power per unit area, and this is not measured in electron-volts. With individual photons we talk about their energy, which can be measured in electron-volts, but the energy of a photon doesn’t oscillate. – G. Smith May 9 at 5:59
• We can still covert unit from J to eV though it may not have a valuable meaning in the classical context. – ggcg May 9 at 17:43
• There is no way to know as context is lacking. – my2cts May 9 at 19:29
• @G.Smith: That should be an answer. – Ben Crowell May 14 at 20:05
• @BenCrowell OK, I’ve made it an answer. – G. Smith May 14 at 21:16

With electromagnetic waves, we talk about peak or average power per unit area, but this is not measured in electron-volts. With individual photons, we talk about their energy, which can be measured in electron-volts, but the energy of a photon doesn’t oscillate.

"Since EM waves oscillate, is the energy given in Ev an average or maximum value?"

This is in reference to classical electrodynamics as I interpret it. It is customary to evaluate the root mean square value of the wave, based on the average of the amplitude square over one cycle. The average of the amplitude will in fact be zero.

"In a related question, can a detector (of whatever sort) 'miss' an Em wave if the amplitude is at a minimum when it goes past the detector?"

To answer this you need to specify how the detector works. Typically a detector will sample the incoming wave over many cycles. Even if it gets a portion of a cycle it will get bombarded with energy. For your assumed scenario to occur you would have to (1) have the detector turn on and off in zero delta time, and (2) synchronize the arrival of the EM wave node with the detector trigger. The latter is unlikely and the former, likely impossible.

• Thank you all! Good answers/comments..... – Kurt Hikes May 11 at 18:25
• This answer misses the main point that needs to be addressed, which is that the energy doesn't oscillate. – Ben Crowell May 14 at 20:04
• Based on the wording of the OP my answer directly addresses the question. – ggcg May 14 at 21:54