Can Photons Really Have Zero Momentum and Energy?

In summary, for photons, the momentum (p) is equal to zero times the speed of light (c), and the kinetic energy (ke) is equal to zero. This is because the formula for energy (E) is equal to the square of the momentum (p) times the speed of light (c) squared plus the rest mass (m) squared times the speed of light (c) to the fourth power, and for photons, the rest mass is equal to zero. This information is explained in more detail in the FAQ and a related thread.
  • #1
suchal
32
1
p=mv then for a photon p=0*c means p=0. And also ke=1/2pv which is ke=0 and E=mc2 means E=0. please use easy words and we descriptive.
 
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  • #2
For <particles> of light, photons, certain care needs to be taken about what p,m,v,E mean. If p=mc, then m is the so-called 'relativistic mass' which has no meaning for a photon, but only for a massive particle.

The universal formula which is to be used is

[tex] E^2 = \vec{p}^2 c^2 + m^2 c^4 [/tex]

where m is the rest/invariant mass which is 0 for a photon.
 
  • #3
See the FAQ here. Also, you might find this thread interesting.
 

FAQ: Can Photons Really Have Zero Momentum and Energy?

Why do photons have momentum?

Photons have momentum because they are particles with energy and mass. According to Einstein's theory of relativity, energy and mass are equivalent, and thus photons possess both. This means that they also have momentum, which is a property of moving objects.

How can photons have momentum if they have no mass?

While photons do not have rest mass, they do have relativistic mass due to their energy. This allows them to have momentum, as momentum is dependent on both mass and velocity. The higher the energy of a photon, the greater its momentum.

Is momentum the same as energy?

No, momentum and energy are two different quantities. Energy is a scalar quantity that represents the ability to do work, while momentum is a vector quantity that represents the motion and direction of an object. However, they are related as energy can be converted into momentum and vice versa.

Do all particles have momentum?

Yes, all particles, including photons, have momentum. According to the law of conservation of momentum, momentum must be conserved in a closed system. This means that the total momentum of all particles in a system must remain constant, regardless of interactions or changes in velocity.

Can photons transfer momentum?

Yes, photons can transfer momentum to other particles through the process of scattering. This is how solar sails work – photons from the sun transfer their momentum to the sail, propelling it forward. Photons can also transfer momentum in the form of radiation pressure, which can be seen in the deflection of comet tails by the sun's photons.

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