The interference patterns observed in a double-slit experiment arise due to the wave-like nature of the particles or waves passing through the slits. When two coherent wavefronts pass through the slits and overlap, they can interfere constructively or destructively, resulting in the observed interference pattern on a screen or detector.
To observe two lines without interference patterns on a double slit, there are a few possibilities:
Non-interfering sources: If you use two independent, non-interfering sources of particles or waves to pass through the slits, you would not observe interference patterns. Each source would create its own distinct pattern on the screen, and the resulting image would be a combination of the two patterns without interference effects.
Incoherent sources: If the sources are incoherent, meaning they do not maintain a fixed phase relationship, interference patterns would not be observed. Incoherent sources can be achieved by using a wide range of wavelengths or by introducing random phase variations.
Partially blocking one slit: By partially blocking or obscuring one of the slits, you can effectively eliminate the interference pattern. This is because the single slit acts as a source of waves or particles, and without the interference between the two slits, you would observe two separate lines corresponding to the two open sections of the double slit.
It's important to note that if you have a setup with two open, coherent slits and no external factors affecting interference, interference patterns would be expected to occur. The interference patterns are a fundamental feature of the double-slit experiment and arise from the wave nature of the particles or waves involved.