1801 – England
‘Interference between waves can be constructive or destructive’
Huygens’ wave theory was neglected for more than a hundred years until it was revived by Young in the opening years of the nineteenth century. Young rejected Newton’s view that if light consisted of waves it would not travel in a straight line and therefore sharp shadows would not be possible. He said that if the wavelength of light was extremely small, light would not spread around corners and shadows would appear sharp. His principle of interference provided strong evidence in support of the wave theory.
In Young’s double slit experiment a beam of sunlight is allowed to enter a darkened room through a pinhole. The beam is then passed through two closely spaced small slits in a cardboard screen. You would expect to see two bright lights on a screen placed behind the slits. Instead a series of alternate light and dark stripes are observed, known as interference fringes, produced when one wave of light interferes with another wave of light.
Two identical waves traveling together either reinforce each other (constructive interference) or cancel each other out (destructive interference). This effect is similar to the pattern produced when two stones are thrown into a pool of water.
The mathematical explanation of this effect was provided by AUGUSTIN FRESNEL (1788-1827). The wave theory was further expanded by EINSTEIN in 1905 when he showed that light is transmitted as photons.
Light, an electromagnetic radiation, is transported in photons that are guided along their path by waves. This is known as ‘wave-particle duality’.
The current view of the nature of light is based on quantum theory.