Final answer:
In physics wave experiments, the phase gradient is altered for each line to ensure unique interference patterns, governed by specific equations including the angle of diffraction and slit spacing.
Step-by-step explanation:
The phase gradient is altered for each line in wave-based experiments to ensure that different points along a wavefront have different path lengths, leading to constructive or destructive interference patterns. This is particularly relevant in the study of diffraction and interference, as demonstrated by the equation d sin θ = mλ (for m = 0, 1, -1, 2, -2, ...), where d represents the slit spacing, θ is the angle of diffraction, and λ is the wavelength of the light. For a diffraction grating with 10,000 lines per centimeter, each line corresponds to a separation of 1/10,000 of a centimeter. By modifying the gradient every certain period of time corresponding to each line, a unique gradient slope is created, generating distinguishable patterns.