Why is monochromatic light used in the double slit experiment? What would happen if white light were used?

The double slit experiment is a demonstration of the wave properties of light, specifically the phenomenon of interference. In this experiment, light from a single source is directed towards a barrier with two narrow slits. The light passing through the slits creates an interference pattern on a screen placed behind the barrier, with alternating bright and dark regions called fringes.

Interference occurs when two or more waves combine, either constructively or destructively. Constructive interference happens when the peaks of the waves align, resulting in a brighter region (a fringe), while destructive interference occurs when the peaks of one wave align with the troughs of another, canceling each other out and resulting in a dark region. For clear interference patterns, it is essential that the light used in the experiment is monochromatic, meaning the light consists of only one wavelength or color. Monochromatic light allows for consistent and predictable interference patterns since the waves are coherent, having a constant phase relationship between each other.

Monochromatic light consists of a single wavelength or color, while white light is a combination of multiple wavelengths or colors spanning the entire visible spectrum. White light is incoherent because the different wavelengths do not have a constant phase relationship with each other, making it unsuitable for creating clear interference patterns.

If white light were used in the double slit experiment instead of monochromatic light, the interference pattern formed on the screen would be less clear and more challenging to analyze. Each wavelength or color of light would create its own interference pattern, resulting in overlapping and blurry patterns on the screen. There may still be a central bright fringe due to all colors constructively interfering, but the other fringes would be less distinct and increasingly more colorful as you move away from the center. In conclusion, monochromatic light is used in the double slit experiment to ensure coherent waves with a constant phase relationship, leading to clear and predictable interference patterns. Using white light would result in multiple overlapping patterns, making it difficult to study the wave properties of light through interference.