In a Young double-slit experiment, when a monochromatic light source is replaced by a source of white light, several changes occur.
Interference pattern: With monochromatic light, you observe a series of bright and dark fringes on the screen due to constructive and destructive interference of the waves. However, when white light is used, the interference pattern becomes more complex. This is because white light is composed of a broad spectrum of wavelengths (colors), each with its own interference pattern. As a result, you'll see a series of colored fringes instead of a simple pattern of bright and dark fringes.
Color dispersion: The white light passing through the double slits will diffract and spread out into its component colors due to the different wavelengths of light bending by different amounts. This effect is known as dispersion. As a result, you will observe a spectrum of colors on the screen, with shorter wavelengths (blue/violet) being bent more and appearing closer to the central bright spot, while longer wavelengths (red) are bent less and appear farther away.
Blurring of fringes: Since the different wavelengths of light create separate interference patterns, the fringes for each color may overlap and blur together. This blurring occurs because the different wavelengths have slightly different spacing between their bright and dark fringes, causing them to interfere differently and mix on the screen. As a result, the individual fringes become less distinct and blend into a multicolored pattern.
Overall, the replacement of monochromatic light with white light in a Young double-slit experiment leads to the formation of a complex interference pattern consisting of multiple colored fringes, with the colors being dispersed and the fringes becoming less distinct due to the mixing of different wavelengths.