Final answer:
In a double-slit experiment, the formula for calculating path-length difference (ΔL = d sin θ) is the most useful for determining the phase difference.
Step-by-step explanation:
To calculate the phase difference for light originating from two slits, such as in a double-slit experiment, the most useful tool would be a formula. Specifically, the formula ΔL = d sin θ, where ΔL is the path-length difference, d is the distance between the slits, and θ is the angle of interference, can be applied. This formula directly relates the geometrical setup of the slits with the resultant phase difference between the two paths, which is essential to analyze data and establish the interference pattern on the screen.
A graph can visually represent the interference fringes produced by the light from the two slits, allowing us to determine the phase difference between them. By analyzing the pattern on the graph, we can calculate the phase difference and understand the behavior of the interference. This information helps us study the phenomenon of double-slit interference and analyze the diffraction pattern.