CBSE NOTES CLASS 12 PHYSICS
CHAPTER 11 DUAL NATURE OF RADIATION AND MATTER
Particle nature of light: the photon
- In interaction of radiation with matter, radiation behaves as if it is made up of particles called photons.
- Each photon has energy E (= h ν) and momentum p (= ), and speed c, the speed of light.
- All photons of light of a particular frequency ν, or wavelength λ, have the same energy E (= h ν = ) and momentum p (= = ), whatever the intensity of radiation may be. By increasing the intensity of light of given wavelength, there is only an increase in the number of photons per second crossing a given area, with each photon having the same energy. Thus, photon energy is independent of intensity of radiation.
- Photons are electrically neutral and are not deflected by electric and magnetic fields.
- In a photon-particle collision (such as photon-electron collision), the total energy and total momentum are conserved. However, the number of photons may not be conserved in a collision. The photon may be absorbed or a new photon may be created.