Photon

[ovi issac]

If photon has no rest mass how it could have relativistic mass which is actually apprent mass added to the mass in motion .

[Strange]

Relativistic mass is just a measure of energy. For a particle with mass, this will be the kinetic energy it gains from its motion. For a photon, it is the energy the photon has, which is proportional to its frequency: https://en.wikipedia.org/wiki/Photon_energy

[Vmedvil]

Yes, all of a photons Energy-mass is from movement that is why you get the colors, different frequencies, each frequency of photon has a different amount of energy the higher the frequency the higher the energy. The reason for this is that the higher the frequency of the photon the more spin/vibration kinetic energy of the photon thus more energy stored in the system, all photons travel at C, but not all photons spin/vibrate at the same speed. The Plank's constant is a measurement  h shows the ratio of spin/vibration with the equation  E=hf for light energy which is stored not as mass but spin/Vibration. There is a more detailed version of the equation below, which shows the movement upon all dimensions of a photon to energy, this what the simplified form E= hf is formed from this differential equation, Einstein just simplified it. 

 

Edited September 27, 2017 by Vmedvil

[swansont]

1 hour ago, Vmedvil said:

Yes, all of a photons Energy-mass is from movement that is why you get the colors, different frequencies, each frequency of photon has a different amount of energy the higher the frequency the higher the energy. The reason for this is that the higher the frequency of the photon the more spin/vibration kinetic energy of the photon thus more energy stored in the system, all photons travel at C, but not all photons spin/vibrate at the same speed. The Plank's constant is a measurement  h shows the ratio of spin/vibration with the equation  E=hf for light energy which is stored not as mass but spin/Vibration. There is a more detailed version of the equation below, which shows the movement upon all dimensions of a photon to energy, this what the simplified form E= hf is formed from this differential equation, Einstein just simplified it. 

 

Spin has a meaning in physics, and the spin of all photons is the same. They are spin-1 particles.

[Vmedvil]

3 minutes ago, swansont said:

Spin has a meaning in physics, and the spin of all photons is the same. They are spin-1 particles.

 

Yes, that has to do with symmetry it can be turned 360 degrees before seeing itself, but I was trying to explains this in Newtonian mechanics by spin I mean Angular Velocity. 

[swansont]

1 hour ago, Vmedvil said:

 

Yes, that has to do with symmetry it can be turned 360 degrees before seeing itself, but I was trying to explains this in Newtonian mechanics by spin I mean Angular Velocity. 

Then you want to look at polarization, and angular momentum. 

[Itoero]

On ‎23‎-‎9‎-‎2017 at 9:37 PM, ovi issac said:

If photon has no rest mass how it could have relativistic mass which is actually apprent mass added to the mass in motion .

he answers his own question...

 

[Blaxtor]

Hi! Einstein theory states E=mc2. The photon has Energy, shouldnt he have a mass then? 

[Sensei]

3 minutes ago, Blaxtor said:

Hi! Einstein theory states E=mc2. The photon has Energy, shouldnt he have a mass then? 

Yet another who don't see difference between rest-mass and relativistic-mass...

Matter can be put to rest, decelerated, and we (observer/device) are at the same frame-of-reference (FoR) as that object. Then mass (rest-mass) is measured.

Rest-mass of electron (or positron) is m_e=9.11*10^-31 kg

So energy that can be released during annihilation of electron-positron is 2m_ec²

They will be in form of two gamma photons typically.

2m_ec² = 2hf_c

Electron/positron before annihilation are in the same FoR as we are, after annihilation newly created gamma photons will be flying at speed of light..

 

[Strange]

17 minutes ago, Blaxtor said:

Hi! Einstein theory states E=mc2. The photon has Energy, shouldnt he have a mass then? 

That equation is only for stationary objects with mass. The full form is [math]E^2 = (m_0 c^2)^2 + (pc)^2[/math]. (where p = momentum). For a photon this is E = pc.

https://en.wikipedia.org/wiki/Mass–energy_equivalence#Applicability_of_the_strict_mass.E2.80.93energy_equivalence_formula.2C_E_.3D_mc2

 

Edited October 3, 2017 by Strange

[Janus]

4 minutes ago, Blaxtor said:

Hi! Einstein theory states E=mc2. The photon has Energy, shouldnt he have a mass then? 

E=mc² has a specific meaning where "m" stands for the rest(or invariant) mass.   Its only meant for those cases when there is a rest mass and that mass has no motion with respect to the measurer. It deals with a limited case of the more general formula:

E²= (pc)²+(mc²)²

Here p stands for the relativistic momentum.  For light, m=0, but that still leaves (pc)².  Light does have a momentum (While in Newtonian physics you can't have momentum without mass, this is not the case in relativity.), so it has energy even though it has no mass.

[Blaxtor]

Thank you for the detailing! it is about definition of rest mass and momentum then. I found this interesting article regarding this question. 

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

[Strange]

John Baez is always worth reading.

[Blaxtor]

Still, for me the momentum of a photon is not clear idea.. How can it be represented if not as newtonian momentum?

Another question is what if we place ourself in the frame of reference of the photon. Would it then have no speed and a mass? Is it even possible or would it contradict physical laws?

Cheers,

[swansont]

4 hours ago, Blaxtor said:

Still, for me the momentum of a photon is not clear idea.. How can it be represented if not as newtonian momentum?

Another question is what if we place ourself in the frame of reference of the photon. Would it then have no speed and a mass? Is it even possible or would it contradict physical laws?

Cheers,

A photon is not a Newtonian particle, it's a quantum particle. One should not be surprised that Newtonian physics doesn't apply.

EM waves having momentum is part of classical theory.