C1

• wave speed = frequency x wavelength
• Phase difference tells you how much a wave is in front or behind another wave with the same frequency and wavelength.
• Path difference

  • interference patterns also depend on the path difference of these overlapping diffraction waves.
  • The path difference is the difference in distance that two waves have travelled to get to a particular point.
• Grating and visible light

  • Gratings can separate light into new diffracted waves
  • When a white light source is diffracted through a diffraction grating, the emissions spectrum of light is formed
• Energy levels in atoms

  • atom is given energy - by heating, passing an electric current through it or absorbing a photon - it emits light of a certain colour
  • The electrons can absorb an amount of energy and become excited, which means they move to a higher energy level
  • The electrons can emit an amount of energy, when the excited electron moves back to the ground state. The light produced is of a specific frequency. This will change depending on the element
• Emissions spectra

  • When gas is heated, the electrons in atoms are excited through collisions with neighbouring particles.
  • The electrons in the atom then de-excite emitting photons.
  • Because the atoms have fixed energy levels, only certain photons can be emitted
  • This means only certain frequencies and wavelengths can be emitted
  • Each element has its own set of energy levels, so emits its own set of photons. We see these photons as lines with specific colours. This means the spectra can used to identify elements