University of Duhok College of Sincse Physics Department Interaction of Light with Matter How does photon interact with mater? Prepared by group B6 - Partizan Fariq - Awaz Mohamed - Heleen Nawzad - Rojman Kamal - Basma Lawrance - Halat Supervised By : Dr. Mohamed Ibrahim Light and Matter • Three ways light interacts with matter Reflection Transmission (Refraction) Absorbtion Reflection and Refraction Interaction of photon with matter (Absorbtion and scattering) # COHERENT SCATTERING • Is also known as classical scattering or Rayleigh scattering. • In coherent scattering : Low energy rediation encounter electrons Electrons are set into vibration Vibrating electrons, emits rediation Atom returns to it’s undisurbed state #Compton Scattering • discovered by Arthur Holly Compton, is the scattering of a photon by a charged particle, usually an electron. It results in a decrease in energy (increase in wavelength) of the photon called the Compton effect. Part of the energy of the photon is transferred to the recoiling electron. #Photoelectric effect • Definition : the phenomenon of emission of electrons by the metals when they are exposed to light of suitable frequency is called as the photoelectric effect and emitted electrons are called as photoelectrons. #Pair Pruducrion • Pair pruducrion is a phenomena in wich a photon with energy more that 1.022 MeV converted into an electron and positron when it passes near a nucleus of an atom What Happens to the matter when a photon interact with it? • Excitation: when a photon falls on an electron with the energy equal to the difference between two energy levels, the electron absorb the photon and jumps to higher energy state, this phenomenon called excitation. Then the electron de-excitation to it’s stat emitting a photon with same energy of absorbed photon . • This is also called scattering • Ionization: when the photon has that energy to eject an electron from the atom, the atom loss an electron and become a positive ion, . this process called Ionization by photons. • Heat: • When light energy hits an object, some of the energy is absorbed by the object. This energy makes the molecules of the object vibrate faster. If we touch the object, we feel this vibration as heat. Thanks for listening