## photon

The massless particle that, according to the quantum theory of radiation, carries the smallest discrete amount of electromagnetic energy

*h*ν, where*h*is Planck's constant and ν is the frequency of the associated electromagnetic wave.Although the photon has no mass it does have (linear) momentum

*h*ν/*c*, where*c*is the free- space speed of light, and intrinsic angular momentum (spin)*h*/2π, as evidenced by radiation pressure and radiation torque.