Final answer:
Interference fringes are less visible in thick glass due to significant path differences causing light waves to be out of phase over various wavelengths. Using monochromatic light can improve the visibility of these fringes due to the consistency in wavelength creating clear interference patterns.
Step-by-step explanation:
It is much more difficult to see interference fringes for light reflected from a thick piece of glass than from a thin film because in thicker glass, the paths that the reflected light waves take from the front and back surfaces are significantly longer, leading to a larger path difference. This large path difference causes the light waves to be out of phase with one another over a wider variety of wavelengths, resulting in less distinct or visible fringes.
Using monochromatic light would indeed make it easier to observe the interference fringes, even in a thick piece of glass. This is because monochromatic light consists of a single wavelength, allowing for a consistent path difference between the light waves reflected from the two surfaces, which makes the constructive and destructive interference patterns more distinguishable.