Young's double slit experiment

• Young's double slit experiment demonstrates the interference of light from 2 sources.
• Diffraction occurs when a a coherent source of light is shone through 2 slits, ensuring the slits are similar in size to the wavelength of the light.
• Each slit acts a secondary source of coherent light wavefronts, causing all the diffracted light to start their cycles at the same position.
• Where light meets constructively, (with a path difference of n(wavelength) where n is an integer), bright fringes occur.
• Where light meets destructively, (with a path difference of n+1/2(wavelengths) where n is an integer), dark fringes occur.
• As the light must be coherent, it can either originate from a laser, or from an incoherent source passed through a colour filter.
• A single slit is placed before the double slits to focus the light, this is unnecessary if a laser is used, as the light can be focussed onto the double slits.
• w = (wavelength * D) / s
• w = fringe separation (between 2 bright fringes)
• D = distance from double slits to screen