# The Naked Scientists Forum

### Author Topic: How can a photon have a frequency?  (Read 2962 times)

#### aasimz

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##### How can a photon have a frequency?
« on: 04/09/2015 14:51:35 »
Hello Pete,

I have a question which I found to be mind boggling, considering the difference between high energy photons and low energy ones, the only difference between them is the wavelength, from what I understand the shorter the wavelength the higher the energy, which means the higher the frequency the higher the energy would be.

The question is, since this is attributed to the frequency of photons not their energy state:

- Why do they use terms like high energy photons
- Is there is such thing as single high energy photon or low energy photon
- Is this a correct phrase "The only difference between colors is that how many photons we receive at the same period of time ie. 100 photon per second has lower energy from 1000 photons per second"
- Is this a correct phrase "All single photons have the same energy state"

That is all, thank you for the opportunity
« Last Edit: 04/09/2015 18:20:23 by chiralSPO »

#### PmbPhy

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##### Re: Subject changed to deleted
« Reply #1 on: 04/09/2015 15:03:18 »
Quote from: aasimz
Hello Pete,

I have a question which is mind boggling for me, considering the difference between high energy photons and low energy ones, the only difference between them is the wavelength, from what I understand the shorter the wavelength the higher the energy, which means the higher the frequency the higher the energy would be.

The question is, since this is attributed to the frequency of photons not their energy state:

- Why do they use terms like high energy photons
- Is there is such thing as single high energy photon or low energy photon
- Is this a correct phrase "The only difference between colors is that how many photons we receive at the same period of time ie. 100 photon per second has lower energy from 1000 photons per second"
- Is this a correct phrase "All single photons have the same energy state"

That is all, thank you for the opportunity
The only questions that I'll be asking him are those regarding common misconceptions and questions I don't already know the answer to. In this case the answers are as follow:

Quote from: aasimz
- Why do they use terms like high energy photons
I don't see that term used much but it obviously refers to photons having high energy where "high" is really a vague term.

Quote from: aasimz
- Is there is such thing as single high energy photon or low energy photon
High and low are relative terms. It's like saying "high energy proton" which simply means a proton having a very high energy according to some standard which dictates what's high and low.

Quote from: aasimz
- Is this a correct phrase "The only difference between colors is that how many photons we receive at the same period of time ie.
No. Color is a function of frequency. Red photons are different from blue photons in that the former have lower energy than the later.

Quote from: aasimz
- Is this a correct phrase "All single photons have the same energy state"
No.

#### aasimz

• Jr. Member
• Posts: 42
##### Re: Subject changed to deleted
« Reply #2 on: 04/09/2015 15:58:00 »
Okay, now it is definitely less confusing, but there is one thing I still did not grasp yet.

What is the difference between a single red photon and a single blue photon? since the function of frequency needs multiple photons (right?), i.e.. I can see that the difference in spin can be attributed to a single particle, but I don't understand how can single photons have different states of energy (different wavelengths).
« Last Edit: 04/09/2015 16:05:07 by aasimz »

#### alancalverd

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##### Re: Subject changed to deleted
« Reply #3 on: 04/09/2015 16:25:50 »
A red photon is a photon with energy < 2 eV, a blue photon has energy > 2.5 eV.

#### aasimz

• Jr. Member
• Posts: 42
##### Re: Subject changed to deleted
« Reply #4 on: 04/09/2015 16:35:35 »
A red photon is a photon with energy < 2 eV, a blue photon has energy > 2.5 eV.

Thank you Alan, but I think that doesn't answer my question:

How can single photons have different states of energy (different wavelengths), since the function of frequency needs multiple photons.
« Last Edit: 04/09/2015 18:16:06 by aasimz »

#### chiralSPO

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##### Re: Subject changed to deleted
« Reply #5 on: 04/09/2015 17:50:48 »
The function of frequency does NOT need multiple photons. The frequency and the energy of a single photon are proportional to one another. Photons are usually released or absorbed one at a time (one photon per event), and the energy of that event is often well-defined, meaning the energy (frequency) of a single photon is often well-defined (instances in which the frequency is not well defined have to do with uncertainty, which we won't get into here)

#### aasimz

• Jr. Member
• Posts: 42
##### Re: Subject changed to deleted
« Reply #6 on: 04/09/2015 18:12:31 »
The function of frequency does NOT need multiple photons. The frequency and the energy of a single photon are proportional to one another. Photons are usually released or absorbed one at a time (one photon per event), and the energy of that event is often well-defined, meaning the energy (frequency) of a single photon is often well-defined (instances in which the frequency is not well defined have to do with uncertainty, which we won't get into here)

I think this is a good step toward unveiling my confusion, :)

How can a single photon have a frequency?, I mean what is it that comes in frequently? i.e. if I am knocking on my table in a specific frequency, in that case the knocks is the thing that come in frequently, the faster I knock, the higher the frequency, right?
« Last Edit: 04/09/2015 18:16:02 by aasimz »

#### chiralSPO

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##### Re: Subject changed to deleted
« Reply #7 on: 04/09/2015 18:18:05 »
a photon is the smallest possible nonzero amplitude of an electromagnetic wave. The frequency refers to how quickly that wave oscillates. More photons means greater amplitude (if they're in phase), but as long as all the photons have the same frequency, the light will have that frequency, no matter how many photons are involved.

#### Bill S

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##### Re: How can a photon have a frequency?
« Reply #8 on: 04/09/2015 22:04:19 »
Aasimz, would it help if you tried thinking of a photon as a wave packet; with more than one wave per photon, frequency is no problem.

As a non-expert, I don't know if that's technically correct, but it helped me.

#### lightarrow

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##### Re: How can a photon have a frequency?
« Reply #9 on: 04/09/2015 23:37:03 »
Bill wrote:
1) "would it help if you tried thinking of a photon as a wave packet; with more than one wave per photon, frequency is no problem."

2) "... I don't know if that's technically correct"

1) and 2) are correct statements

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lightarrow

#### lightarrow

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##### Re: How can a photon have a frequency?
« Reply #10 on: 05/09/2015 08:33:55 »
What is the difference between a single red photon and a single blue photon?
The difference is in the electromagnetic field frequency.
A photon is a "quantum of excitation of the electromagnetic field" and so the photon's frequency is of that em field.

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lightarrow

#### lightarrow

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##### Re: How can a photon have a frequency?
« Reply #11 on: 05/09/2015 08:36:55 »
a photon is the smallest possible nonzero amplitude of an electromagnetic wave.
Which movie is this?

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lightarrow

#### evan_au

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##### Re: How can a photon have a frequency?
« Reply #12 on: 05/09/2015 11:46:45 »
Quote
How can a single photon have a frequency?, I mean what is it that comes in frequently?
A simple analogy that might help here is a plucked guitar string:
• One pulse of energy (the top "thick" string, when plucked) produces a low frequency. You could imagine this like an infra-red photon.
• Another pulse of energy (the bottom "thin" string, when plucked) produces a higher frequency. This might be like a blue photon.
• High frequency and low frequency are relative terms.
• If you pluck a double bass, you can get lower notes than a guitar. (This might be considered like a microwave photon.)
• If you pluck a violin, you can get higher notes than a guitar. (This might be like an X-Ray photon.)
Just like a plucked guitar string produces an oscillating air pressure at a particular frequency, a photon produces an oscillating electric and magnetic field at a particular frequency.

Due to conservation of energy, neither plucked strings nor photon oscillations last forever - you need to keep strumming the guitar, or pumping out new photons from a laser.

#### Thebox

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##### Re: How can a photon have a frequency?
« Reply #13 on: 05/09/2015 12:10:00 »
Hello Pete,

I have a question which I found to be mind boggling, considering the difference between high energy photons and low energy ones, the only difference between them is the wavelength, from what I understand the shorter the wavelength the higher the energy, which means the higher the frequency the higher the energy would be.

The question is, since this is attributed to the frequency of photons not their energy state:

- Why do they use terms like high energy photons
- Is there is such thing as single high energy photon or low energy photon
- Is this a correct phrase "The only difference between colors is that how many photons we receive at the same period of time ie. 100 photon per second has lower energy from 1000 photons per second"
- Is this a correct phrase "All single photons have the same energy state"

That is all, thank you for the opportunity

Hello, I think I understand you, you are asking why and where a frequency comes from when a rate can only be established via consistency and a constant rate and a plural of photon is needed to define a wavelength frequency.  Frequency is a result of propagation  or a constant energy release such as radio waves etc, if you can imagine a single photon and another photon travelling symmetric to each other, the net charge of either photon is zero, and when these photons interact with something this creates a net charge, so if you can imagine billions of photons travelling through space with no space between them, you can imagine what happens when there is something obstructing their journey, their will be a congestion of photons .  Although the congestion moves very fast, it is just enough to propagate the radiation and cause  a change of the constant, you can see the frequencies if you look around you in the form of spectral colours, where the un-propagated light you see in the space between masses, you see through, this is because light in space with no propagation is at an equilibrium to your sight, and the frequencies you see , are seeing a change in the constant.
Hope this helps you , I am not a scientist and this just my humble opinion.

#### The Naked Scientists Forum

##### Re: How can a photon have a frequency?
« Reply #13 on: 05/09/2015 12:10:00 »