Final answer:
Monochromatic light is used in the double-slit experiment to produce simple and stable interference patterns, as it contains only one wavelength. White light, which has multiple wavelengths, would create a complex and messy interference pattern that is difficult to analyze.
Step-by-step explanation:
Monochromatic light is used in the double-slit experiment to simplify the interference pattern because it is composed of light with a single wavelength. This consistent wavelength ensures the occurrence of stable and predictable constructive and destructive interference patterns. If white light, which contains multiple wavelengths, were used, each wavelength would form its own pattern, resulting in a complex and messy mixture of interference patterns that would be harder to analyze. This makes it much more difficult to distinguish the interference fringes and understand the wave behavior of light.
Thomas Young originally used sunlight and passed it through a single slit before it reached the double slits to make the light waves somewhat coherent. Coherent light waves have a fixed phase relationship, which is crucial for producing clear interference patterns. The double slits then act as two coherent sources, leading to a distinct pattern of interference fringes. The use of monochromatic light in modern renditions of the experiment further helps to clarify the pure constructive and destructive interference because there are no additional complexities introduced by the presence of multiple wavelengths.