# How do photons induce current in an antenna?

I have done a lot of research on this topic, but I have yet to find a good explanation in plain english (I’m dumb) that answered this for me.

I know that photons have oscillating electric and magnetic fields, and that an electromagnetic wave as a whole consists of many photons.

I know that photons can strike electrons and excite them to a higher energy level (like the conduction band for example). But I’m not taking about that. I’m interested more in antennas and how the photons induce current.

There are two components of photons: the electric field and the magnetic field.

First, I am curious about which field it is that interacts with the electrons (I’ve heard most often that it’s the electric field.

Second:If it’s the electric field that interacts, does it push or repel the electrons? Because photons also interact with protons, so I don’t quite understand how the electric field could push or pull electrons unless it’s negative or positive…

Third: what about when you consider it from a point particle viewpoint(photon acts as a sphere rather than wave I guess..?)? If electrons are jumping up and down shells, how does this induce current in a particular direction? I would think that if electrons in the middle of an antenna (for example) had electrons jump to a higher shell, that electrons from both sides would fill the holes left behind…but current has a direction if that makes sense.. so what determines if the ac current will go left or right?

To sum it up, which field from a photon interacts with electrons to induce current? And from a point particle perspective, how do electrons jumping up and down shells induce current, particularly in such a way that electrons move right one half cycle, and left the next half cycle?

If you need me to clarify anything, please let me know. I am a very dumb dude, so please give me a plain English answer if you can.

• Re, "photon acts as a sphere." That's probably not a helpful image. When we say that a photon is a "point particle" we usually mean two things; "particle" means that photons can be counted, and "point" means that when we detect an individual photon, we can say where it was detected. You should not assume that either of those words means anything more than that. When we're talking about radio-frequency electromagnetic radiation, we can describe it in theory as a stream of photons, but we have no practical technology that actually can detect or localize radio-frequency photons. Sep 10, 2022 at 13:24
• You will find answers to all your questions on the Amateur Radio stack exchange. Lots of helpful people there. Sep 10, 2022 at 18:00
• You may find this helpful: How a radio wave is created Sep 11, 2022 at 4:56

There are a number of misconceptions in your "know"

I know that photons can strike electrons and excite them to a higher energy level(like the conduction band for example).

Photons, as elementary particles, interact with the whole "atom", "molecule", "lattice" and excite them to higher energy states

There are two components of photons: the electric field and the magnetic field.

This is not correct, the only attributes of the elementary photon are its energy, zero charge and spin, a photon has no electric or magnetic field .

First, I am curious about which field it is that interacts with the electrons (I’ve heard most often that it’s the electric field.

Electricity and magnetism, electric and magnetic fields are measured attributes of the electromagnetic radiation which is described very accurately with the classical electrodynamic solutions of Maxwell equations, antennas and everything.

Photons belong to the quantum mechanical level of matter, that was slowly observed and modeled with quantum mechanical equations . It has been proven mathematically that a large number of photons build up quantum mechanically the classical electromagnetic wave, but the individual photon is not an electromagnetic wave, as the individual molecule in a stream is not water but makes up the fluid called "water".

How individual photons build up light can be seen in single photon at a time experiments. See my answer here.

It can be shown mathematically that a large number of photons build up the classical wave and the classical electric and magnetic fields emerge from the quantum mechanical solutions of the wavefunction of the the photon, so the classical equations are adequate to describe and predict the current in an antenna. My answer here goes into that.

second:If it’s the electric field that interacts, does it push or repel the electrons?

See above links, it is the confluence of photons that interacts with the lattice of the antenna and its energy levels.

Because photons also interact with protons, so I don’t quite understand how the electric field could push or pull electrons unless it’s negative or positive…

Another misconception. Photons interact with free protons, protons in the antenna are within nuclei , within neutral atoms, all tied up in a lattice of solid state matter.

So,

To sum it up, which field from a photon interacts with electrons to induce current?

There is no field in the photon. It is the emergent classical electromagnetic light that has fields that can interact with the electrons bound to the whole lattice of the antenna that can be modeled to be almost free within the metal that move with the classical field and a current is generated.

And from a point particle perspective, how do electrons jumping up and down shells induce current, particularly in such a way that electrons move right one half cycle, and left the next half cycle?

It is the almost free electrons bound to the lattice wave functions that are in the conduction band and create the current.

It is not possible to understand physics with hand waving arguments. Mathematics is the language of physics and one has to study it if one is really interested in answers

Step 1: Drop the point particle view of a photon. It's useless and confusing.

I know that photons have oscillating electric and magnetic fields

This is correct.

First: It is the electric field of the photons that interact with electrons in an antenna.

Second: The electric field is a vector. The force that an electric field puts on a charged particle is $$F=qE$$. So since $$q$$ is negative for an electron the electric field puts a force on the electron in the opposite direction as the field is pointing.

Third: The question you ask here is rife with confusion. (1) Don't think of photons as having anything to do with point particles or really particles at all. It doesn't add anything and it just adds confusion. A photon is an excitation of the (quantum) electromagnetic field with the special property that the size of the excitation is quantized. (2) Electrons jumping up and down shells is the wrong picture here. That picture makes sense for electrons transitioning between bound states of an atom. The electrons in an antenna are "free" and not bound.

• I down voted because I didsagree with your agreement, it perpetuates confusions. photons have no electric and magnetic field, their wavefunction is described with the electric and magnetic fields the classical wave made up of that energy photons has. The electrons are bound to the lattice of the antena , in the conduction band. Sep 11, 2022 at 9:25
• Re the electron state: I may be wrong here, but my understanding is that the conduction band is more like a continuum than a set of discrete states. And also that, for this problem, electrons start and end in different conduction band states, so the “shell hopping picture” is not quite appropriate. Even if the problem can be shoehorned into it. Sep 11, 2022 at 13:20
• @annav regarding the views on photons. Yes, from many of your other posts I know you don’t like my view of photons as excitations of the quantum electromagnetic field and you prefer a view centered around: photons being spinful point particles and classical electromagnetic fields are made up of many photons. I would be interested to have a real time discussion about this with you. Sep 11, 2022 at 13:23
• I have the view point of the basic mainstream underlying nature of all theoretical models of physics . the standard model of particle physics, from which all other theories of mainstream physics have to be emergent.. I know for example that the term "photon" is used ad hoc by quantum optics, where their photons have mass. I do not think there is anything to discuss except semantics. Sep 11, 2022 at 13:49
• @annab for me the standard model of particle physics is a misnomer. I’d call it the standard model of quantum fields. A zoo of quantum fields underlies everything from which other theories must emerge. Sep 11, 2022 at 13:56

A sender antenna is in an exited state, like exited atom is in an exited state. At random times it drops to a lower energy state. The change of energy is called a quantum of energy.

A receiver antenna, when near a sender antenna at some times jumps to a higher energy state. The change of energy is called a quantum of energy.

We say the sender antenna emits quantums of energy, and the receiver antenna absorbs those quantums of energy. We say the antennas exchange a photon.

A charged hair attached to a massive head stands straight when there is a large antenna nearby, that is emitting a huge number of photons. The hair does not absorb energy, because it can not move, because it is attached to the head. But it must be absorbing momentum because it is constantly giving momentum to the head.

So therefore every quantum of energy sent by the antenna must come with a quantum of momentum. This momentum must point to direction transverse to the antenna-hair direction, so that the hair will point to that direction.

And the direction of the momentum must change at some frequency, as the hair changes the direction that it is pointing to at some frequency.

Also a magnetic hair, or needle, can absorb some momentum out of those same quantums of momentum.

Did everything get answered? Or nothing? :)

(The "absorption of some momentum from a quantum of momentum" must be a change of direction of momentum vector of the quantum of momentum, because we never run out of momentum when we "absorb momentum")