Does a photon correspond to one wavelength of a wave

In summary, photons (wave packets), have a definite wavelength only when they have a well-defined momentum and energy. When they are in a superposition of momentum eigenstates, the wavelength is spread out and has an uncertainty proportional to Planck's constant divided by p, the magnitude of the momentum.
  • #1
Ratzinger
291
0
a dummy question, but does a photon correspond to one wavelength of a wave...does wave mean one wave length?
 
Science news on Phys.org
  • #2
i don't think so. i think a photon corresponds to a "wave packet". the number of photons per second depends on both the frequency and the intensity of radiation, but the number of wavelengths (cycles) per second depends only on the frequency.
 
  • #3
RBJ is right. A photon is a finite wave train and does not have an exact frequency
but you can can make one with say 10 crests and troughs or 10,000 crests and troughs.
The one with only ten has a less well-defined energy and frequency than the
the one with 10,000 even though they may be centered on the same energy.

The shorter photon will have a broader spectrum and will have taken
1000 times less time to generate.
 
Last edited:
  • #4
Photon corresponds to the particle nature of light and has no defined frequency which is a peculiar feature of a wave. A light possessing energy E will consist of number of photons each possessing energy 'E' , a photon is a packet of energy , and is a particle that moves with 'c' and doesnot exist when at rest.Its a particle that carries a momentum and a force is felt when it strikes a surface.

BJ
 
  • #5
OK, I'll bite into this just to stirr things up... :)

For those who say that a photon is simply a "wave packet", consider the following:

A "wave packet" is made up of a superposition of a number of waves of different wavelength. Not only that, the wave packet moves with the group velocity of the packet, while the phase velocity can be significantly higher.

So how do you reconcile the fact that a photon can carry only ONE wavelength, especially in a monochromatic source (even allowing for a finite spread due to resolution and thermal smearing - these spreadings do no make up the wavepacket)? I can also change the group velocity of the wave packet by mixing in different wavelengths. This means that different frequency mix travels at different speeds. We don't see this in photons with different wavelenths.

Zz.
 
  • #6
I found a very enlightening post in Marlon's journal (hope Marlon doesn't mind that I repost it here)


WHAT IS THE DIMENSION OF A PHOTON ?

You all know that QM provides us with 1 (and not two) way of describing physical processes : particle wave duality. We apply our classical ideas of what "wave" is, and what a "particle" is. A particle, like a grain of sand, has a definite boundary in space, i.e. a grain of sand doesn't appear spread out that it's exact shape and boundary are vague. Thus, it has what we classically define as a particle. A wave, on the other hand, can spread out over space.

Now, here is the clue : A photon description in QM is NOT defined as having an exact shape and boundary in space, thus a photon is NO classical particle. It is defined as clumps of energy. So in energy coordinates, it has definite "points", but it has no definite "size" in real space! So when talking about 'size' of a photon you must realize that we work in energy space (more formally we work with momentum-eigenstates)

Having said that, the most common explanation for the "wave-particle duality" is that light behaves as waves in experiments such as the double slit, and behaves as particles when we do things like the photoelectric effect

A photon has a perfectly well-defined wavelength only when it's in a momentum eigenstate, i.e. when it has a perfectly well-defined momentum (and energy). This never happens. A photon is always in a superposition of momentum eigenstates:



The only quantity that we might want to call the "size" of the photon is the width of the Fourier transform of the momentum-space wave function, f, i.e. the uncertainty in the photon's position. This uncertainty could be anything between zero and infinity. (I'm ignoring Planck-scale effects here). Since it can be arbitrarily close to zero, it makes sense to call the photon a "point particle".

However, if we assume that the uncertainty in momentum is proportional to the magnitude of the momentum (which is the only thing we can assume if we know nothing about the state), the uncertainty in position is proportional to Planck's constant divided by p (the magnitude of the momentum). Since p is inversely proportional to the wavelength, the uncertainty in position is proportional to the wavelength.

So it makes sense to think of the wavelength as the "size" of the photon (or at least as something proportional to it). This may seem strange, but it is at least consistent with e.g. the fact that microwaves (with wavelengths of order 1 cm) won't go through a metal net with millimeter-sized holes (like the net that covers the window of your microwave oven), but they will go through a net with much larger holes.
 
Last edited:

1. What is a photon?

A photon is a fundamental particle of light that carries energy and has properties of both a particle and a wave. It is the basic unit of all electromagnetic radiation, including visible light.

2. How is a photon related to a wave?

A photon can be described as a wave packet, which means it has both particle-like and wave-like characteristics. This is known as wave-particle duality.

3. Does a photon correspond to one wavelength of a wave?

Yes, a photon corresponds to one wavelength of a wave. The energy of a photon is directly proportional to its frequency, which is inversely proportional to its wavelength. This means that a higher frequency (shorter wavelength) photon carries more energy than a lower frequency (longer wavelength) photon.

4. Why is the concept of a photon important?

The concept of a photon is important because it helps us understand the properties and behavior of light and other forms of electromagnetic radiation. It also plays a crucial role in many areas of modern science, such as quantum mechanics and the study of light-matter interactions.

5. Can a photon have more than one wavelength?

No, a photon can only have one wavelength because it is a discrete packet of energy. However, a beam of light can contain multiple photons with different wavelengths, which gives it the appearance of having multiple wavelengths.

Similar threads

Replies
10
Views
2K
Replies
7
Views
761
Replies
12
Views
1K
Replies
28
Views
3K
Replies
88
Views
23K
Replies
3
Views
1K
Replies
54
Views
5K
Replies
9
Views
1K
Replies
35
Views
8K
Back
Top