A photon’s rest mass is considered exactly zero (0). This me
A photon’s rest mass is considered exactly zero (0).
This means the photons coming from the Sun do not have mass in the traditional “at rest” sense.
However, photons do carry:
* Energy
* Momentum
Because of this, they can still produce physical effects — such as pushing a solar sail or causing the photoelectric effect.
According to Einstein, the energy of a photon is:
E = h\nu
Where:
* E = energy
* h = Planck’s constant
* \nu = frequency of light
Using the relationship between energy and mass, an “effective relativistic mass” can be calculated for a photon:
m = \frac{E}{c^2}
For a typical visible-light photon from the Sun, this effective mass is approximately:
10^{-36} \text{ to } 10^{-35} \text{ kg}
which is extremely tiny.
For comparison:
* Electron mass ≈ 9.11 \times 10^{-31} kg
* A photon’s effective mass is millions of times smaller.
That is why scientists usually say:
“A photon has zero rest mass, but it carries energy and momentum.”
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