- #1
Ed Aboud
- 201
- 0
Sorry if this is a ridiculous queation, but how does a photon have momentum if it hass no mass?
Crosson said:They do it with energy! The equation for energy in relativity is:
[tex] E^2 = m^2 c^4 + p^2 c^2 [/tex]
Where m is the mass, p is the momentum, and c is the speed of light. Put in [itex]m = 0[/itex] and you get E = p c, so any massless particle with energy E will have momentum p = E/c.
Bright Wang said:what is the relationship between P and E?
Usaf Moji said:Another way of getting the same result is to use the more popular form
[tex] E = mc^2 [/tex]
and solve for m (which can be regarded as the "relativistic mass"). Then just multiply by the velocity, which is c, and treat it like any other problem. You'll see that you get the same result, p = E/c.
A photon is a type of elementary particle that does not have any rest mass. However, it does possess energy and momentum due to its nature as an electromagnetic wave. According to Einstein's famous equation E=mc^2, energy and mass are interchangeable, and photons have a fixed amount of energy that is directly proportional to its frequency. This energy is what gives a photon its momentum.
The momentum of a photon can be calculated using the equation p = h/λ, where p is the momentum, h is Planck's constant, and λ is the wavelength of the photon. This equation is derived from Einstein's equation E=hc/λ, where c is the speed of light. Since a photon's energy is directly proportional to its frequency, the product of Planck's constant and the speed of light can be used to calculate its momentum.
The momentum of a photon is inversely proportional to its wavelength, meaning that longer-wavelength photons have lower momentum and shorter-wavelength photons have higher momentum. This is in contrast to massive particles, whose momentum is dependent on their mass and velocity. However, both photons and massive particles can have the same momentum if their energies are equivalent.
While the momentum of a photon cannot be directly observed in everyday life, its effects can be seen through phenomena such as radiation pressure and the photoelectric effect. In these cases, the momentum of a photon is transferred to a larger object, causing a measurable change in its motion or energy.
The fact that a photon can have momentum without having mass has significant implications in the fields of physics and cosmology. It allows for the understanding of light and other electromagnetic waves as particles rather than just waves. This concept also plays a crucial role in theories such as quantum mechanics and the Standard Model of particle physics.