Young’s double-slit experiment confirms the wave nature of light by demonstrating interference, a phenomenon unique to waves.
Here’s how:
- Superposition Principle: When coherent light passes through two closely spaced slits, each slit acts as a source of secondary wavefronts. These waves overlap and interfere with each other.
- Constructive Interference: At certain points on the screen, the waves from both slits arrive in phase (their crests and troughs align), producing bright fringes due to increased intensity.
- Destructive Interference: At other points, the waves arrive out of phase (a crest meets a trough), leading to dark fringes where they cancel each other out.
- Fringe Pattern: This alternating pattern of bright and dark bands (interference fringes) is impossible to explain with particle theory, which would predict only two bright spots behind the slits.
- Dependence on Wavelength: The spacing of the fringes depends on the wavelength of light, further reinforcing that light behaves as a wave.
Conclusion:
The experiment’s clear display of interference patterns provides direct evidence that light exhibits wave-like behavior, supporting the wave theory of light proposed by Huygens and later expanded by Maxwell and others.