two source interference

• to get two coherent sources, you should use the same oscillator to drive both sources. for example, for sound waves, one oscillator should be connected to two loud speakers
• young's double slit experiment:

  • either use two separate two coherent light sources, or shine a laser through two slits, onto a screen
  • the slits should be about the same size as the wavelength of the light so that it is diffracted
• young's double slit experiment:

  • you should get a pattern of light and dark fringes, depending on whether constructive or destructive interference is taking place
• Thomas Young came up with an equation to work out the wavelength of the light from his double slit experiment:

  • $w=$$\frac{\lambda D}{s}$
  • $w$ = fringe spacing
  • $\lambda$ = wavelength
  • $D$ = distance from slits to screen
  • $s$ = slit separation
• when using Young's double slit formula, the fringes are very small so it is hard to calculate an accurate value for the fringe spacing. it is easier and more accurate to measure across several fringes and find the average
• Newton's corpuscular theory suggested that light was made up of tiny particles, called corpuscles. Huygens put forward a theory that light is made up of waves.

  Newton's theory could explain reflection and refraction, but not diffraction and interference as they are uniquely wave properties.

  Young's double slit experiment provided the necessary evidence that light behaves like a wave.