An electron and an antielectron (positron) each have a rest energy of 0.511 MeV , or approximately 8.2×10−14 J . When an electron and a positron are both stationary and located next to each other during an annihilation process, their mass energy converts to electromagnetic energy released as photons, electromagnetic particles that have momentum but no mass and that travel at the speed of light. What is the minimum number of photons that could be released, and how much energy would each photon posses?

Explanation:

Photon is also a particle . Hence when two particles like electron and positron annihilate to get completely changed to photons , a minimum of two photons of equal and opposite momentum and energy are produced flying in opposite direction  to conserve momentum and energy . Each photon will have same energy equal to 511 keV . It is so to conserve momentum and energy. Initially total momentum was zero so finally too total momentum should be zero.

show the wavelengths of a wave. show the crests of a wave.