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As per the Einstein equation $E=mc^2$, the energy of the particle is depends on the mass of the particle. Or else in other terms the energy is proportional to the mass. If the photons are having zero (rest) mass, then how the photons are having energy? Can we say the massless particles are also having energy?

Qmechanic
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natarajan physicist
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  • m is the non-relativistic mass and $E = mc^2$ is half the story. For photons, $E = pc$ where p is the momentum and c is speed of light – Fraïssé Jan 27 '15 at 07:44
  • Possible duplicates: http://physics.stackexchange.com/q/6202/2451, http://physics.stackexchange.com/q/2229/2451 and links therein. – Qmechanic Jan 27 '15 at 07:46

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In the equation $E_0=m_0c^2$, the quantity $E_0$ is not the total energy of the particle. Rather, it is the rest energy. The total energy $E$ is given by the equation, $$E^2 = m_0^2c^4 + p^2 c^2$$ where $E$ is the total energy (i.e., rest energy + kinetic energy) and p is the momentum of the particle.

In the case of a photon, $m_0$ is indeed zero; but $p$ is not. $p$ of a photon is given by $\frac{h\nu}{c}$. Substituting this into the above equation will give the familiar $E=h\nu$.

abhisrkckl
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