Question

The equation E = pc is valid
(a) for an electron as well as for a photon
(b) for an electron but not for a photon
(c) for a photon but not for an electron
(d) neither for an electron nor for a photon

Answer 1

The correct answer is option (c), which is not for an electron, and for a photon.

EXPLANATION:

• For a particle with zero rest mass, the equation E = pc is effective. The photon’s rest mass is zero, but an electron’s rest mass is not zero. So, the equation will not be valid for an electron, but valid only for a photon.  

• In Physics, a particle’s Energy-Momentum relation is shown as below:  

• Here, p is the momentum,   is the particle’s rest mass, E is the energy, and c is the light’s velocity.  

• For Photon, there is valid   and   = 0. For electron,   is not valid because  .