Diffraction gratings

• Diffraction

  The tendency of a wave to spread out in all directions, transferring energy to its surroundings.
• Diffraction grating

  A flat plane object with a series of regular lines formed on it that block parts of an advancing wave.
• Diffraction

  When an advancing wave encounters a flat obstacle, like a wall, the waves energy is either absorbed/reflected by the wall. If it has edges or gaps the wave energy can travel around the edges of through the gaps (diffraction occurs.)
• Diffraction grating

  When a wave meets a diffraction grating, some of the wave energy continues moving forward through the gaps (transmission). Some wave energy may be absorbed by the grating itself, but the remainder energy is scattered backwards as a reflection.
• Superposition

  Adding together of wave displacements that occurs when waves from two or more separate sources overlap at any given location.

  Coherent: Means when two waves stick together when they are superposed which gives a visible interference pattern.

  The waves must have the same frequency and wavelength and a constant phase difference.
• Coherent light sources


  Light emitted is absorbed by matter, think of light as packets of energy called photons.
• Emission spectra

  When a chemical element/compound is vaporised by heating in a flame and pass an electric current at high voltage through the gas, you see light emitted of a specific colour.

  By looking at that same colour using a spectrum of light from a prism or a diffraction grating you'll see a number of bright coloured lines at definite frequencies. These "lines" match to the photons emitted from the gas electricity with nearly the same frequency and energy.