# The Naked Scientists Forum

### Author Topic: How big is a photon of Very Low Frequency radio waves?  (Read 7686 times)

#### Bruce Horsburgh

• Guest
##### How big is a photon of Very Low Frequency radio waves?
« on: 11/02/2011 22:30:03 »
Bruce Horsburgh  asked the Naked Scientists:

Chris, et al.

I was listening to a pod cast this morning this morning while running to work, and it suddenly occurred to me...

If photons are packets of light that have size but no mass, and if light is just part of the electromagnetic spectrum, then how big is a photon of Very Low Frequency radio waves?

Thanks

Bruce

What do you think?
« Last Edit: 11/02/2011 22:30:03 by _system »

#### Soul Surfer

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• keep banging the rocks together
##### How big is a photon of Very Low Frequency radio waves?
« Reply #1 on: 11/02/2011 23:39:07 »
it is in effect very large even though its energy is very small.  The simplest visualisation of a photon is a few wavelengths of the frequency it is so for the hyperfine line of atomic hydrogen (which at 1400 MHz has a wavelength of around 21cm you can think they are around one meter across.  however this does not prevent them from being absorbed and emitted by individual atoms (as they are)many orders of magnitude smaller than this.   This spectrum line is very important in studying the universe at radio frequencies.

#### bardman

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• Posts: 35
##### How big is a photon of Very Low Frequency radio waves?
« Reply #2 on: 16/02/2011 21:59:37 »
I was under the impression that photons have no actual volume (in the sense we think of), because photons cannot technically "crash" into each other. However, they do have an area in which the effects of their wave function are non-zero and this would basically be their wavelength. Is this true, that there is no actual volume, only an area with nonzero probability for location?

#### JP

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##### How big is a photon of Very Low Frequency radio waves?
« Reply #3 on: 17/02/2011 19:42:52 »
There are a couple of problems with defining the concept of volume for quantum particles.

When a fundamental particle such as a photon actually interacts with something it does so as a point, as far as we can tell.  In that case, we model it as having zero volume.

But in between interactions, it's smeared out over some region of space, and is described by a wave function that tells you the probability of finding that point particle at each point in space.  In that case, you could define the volume in which you're X% likely to find the particle, and call that the particle's volume.

Photons are a bit tricker because of the way we describe them.  Approximating them as a few wavelengths of a field is good in some circumstances, but the technical definition of a photon is a wave function over all space.  I think that when photons are being sent from a source to a receiver, you end up being highly likely to see them at a certain point in space, which corresponds to the few-wavelength approximation.

#### bardman

• Jr. Member
• Posts: 35
##### How big is a photon of Very Low Frequency radio waves?
« Reply #4 on: 18/02/2011 20:18:30 »
Right. So a good approximation of their volume (if just traveling through space) is where most of their wave function is concentrated? Then, when doing interactions, we consider their volume zero?

#### The Naked Scientists Forum

##### How big is a photon of Very Low Frequency radio waves?
« Reply #4 on: 18/02/2011 20:18:30 »