In Young's double-slit experiment, when a barrier is placed between the two slits, the interference pattern that would typically be observed is disrupted. The interference pattern consists of alternating bright and dark fringes produced by the superposition of waves from the two slits.
When a barrier is inserted, it prevents the waves from one slit from reaching the other slit directly. This means that the waves no longer interfere with each other, resulting in the disappearance of the interference pattern. Instead, two separate diffraction patterns are observed, each corresponding to the individual slits.
The significance of this observation is that it provides evidence for the wave nature of light and the principle of superposition. When the barrier is removed, and the two slits are allowed to act as sources of coherent light waves, the interference pattern reappears. This behavior suggests that light exhibits wave-like properties, as it undergoes interference, just like water waves or sound waves.
The double-slit experiment with or without a barrier has been instrumental in demonstrating the wave-particle duality of light and matter. The observation of interference patterns when the barrier is absent supports the wave nature of light, while the absence of interference when the barrier is present suggests that the wave nature of light is disrupted or obscured in such cases.
Overall, the double-slit experiment and its variations have played a crucial role in shaping our understanding of quantum mechanics and have raised fundamental questions about the nature of particles and the role of observation in determining their behavior.