Final answer:
If light passed through round holes in a spectroscope, it would produce thicker spectral lines compared to slits. Diffraction gratings are chosen over slits for sharper and brighter bands. Monochromatic light makes it easier to see interference fringes from reflected light.
Step-by-step explanation:
If light in a spectroscope passed through round holes instead of slits, spectral lines would appear as thicker lines. This is because the diffraction pattern produced by a round aperture spreads out more than that from a slit, causing the resulting bands to be broader. Diffraction gratings are used in spectroscopes rather than just two slits because the bands produced by diffraction gratings are brighter and sharper than the bands produced by two slits which leads to more precise spectroscopy results. When the number of lines per centimeter on a diffraction grating is increased, the interference pattern spreads farther from the central maximum, resulting in a greater dispersion of wavelengths and a more finely detailed spectrum.
Interference fringes are more difficult to see when light is reflected from a thick piece of glass because there is a greater range of path lengths over which the light waves can interfere, leading to a blurring of the interference pattern. With monochromatic light, which has a single wavelength, it becomes easier to observe clear interference fringes because there is less variation in the path length differences required for constructive or destructive interference.