Final answer:
Observing interference fringes in thick glass is difficult due to the large optical path differences and loss of coherence from multiple reflections. Monochromatic light simplifies the pattern by providing a single wavelength that makes constructive or destructive interference clearer and easier to see.
Step-by-step explanation:
The question addresses the phenomenon of light interference, particularly the difficulty in observing interference fringes when light is reflected from a thick piece of glass in comparison to a thin film.
It is indeed much more difficult to see interference fringes with a thick piece of glass because the optical path difference for the numerous beams reflecting internally can be very large, resulting in a multitude of overlaid fringes which are difficult to resolve visually. Furthermore, coherence is lost due to the multiple reflections and varying path lengths.
Using monochromatic light, which consists of a single wavelength, can significantly simplify the pattern and make the fringes easier to see because it eliminates the overlap of different colors that would further complicate the interference pattern.
Monochromatic light would result in a more straightforward constructive or destructive interference, which could be observed as distinct fringes.