Final answer:
When the number of slits in a double-slit experiment is increased, the number of fringes on the screen will increase, the fringe spacing will stay the same, the width of each fringe will decrease, and the brightness of each fringe will decrease.
Step-by-step explanation:
When the number of slits in a double-slit experiment is increased, the interference pattern on the screen will still consist of multiple fringes, but the number of fringes will increase. This is because each individual slit will produce its own set of fringes, and when there are more slits, there will be more sets of fringes overlapping each other.
The spacing between the fringes, also known as the fringe spacing, will remain the same. The width of each fringe, however, will decrease. This is because the total width of the interference pattern is determined by the viewing angle and the distance between the slits, and when there are more slits, the total width of the pattern remains the same, causing each individual fringe to be narrower.
The brightness of each fringe will also decrease. This is because the intensity of the interference pattern is determined by the superposition of the waves from each slit, and when there are more slits, the superposition becomes less pronounced, resulting in a decrease in brightness.