When an object is moved closer to or further away from a double slit in the double-slit experiment, the number of fringes that appear on the screen can change. The fringes in the double-slit experiment refer to the alternating bright and dark regions that result from the interference of waves.
The fringe pattern is determined by the wavelength of the waves and the geometry of the experiment. In the case of light passing through the double slit, the interference pattern arises from the constructive and destructive interference of the light waves.
If the object (e.g., a screen or detector) is moved closer to the double slit, the distance between the slits and the screen decreases. As a result, the fringe pattern on the screen becomes more spread out or wider. This is because the decreased distance increases the angle at which the waves from each slit reach different points on the screen, leading to a larger separation between bright and dark fringes.
Conversely, if the object is moved further away from the double slit, the distance between the slits and the screen increases. In this case, the fringe pattern becomes more compressed or narrower. The increased distance reduces the angle at which the waves from each slit reach different points on the screen, resulting in a smaller separation between bright and dark fringes.
It's important to note that the overall size of the fringe pattern is also influenced by the wavelength of the waves. Shorter wavelengths (e.g., blue light) produce a narrower fringe pattern, while longer wavelengths (e.g., red light) result in a wider fringe pattern.
In summary, moving the object closer to the double slit spreads out the fringes, while moving it further away compresses the fringe pattern.