Double-slit diffraction and double-slit interference are related phenomena, but they are not exactly the same thing. They both arise from the interaction of waves passing through two closely spaced slits, but they have distinct characteristics.
Double-slit interference refers to the pattern of alternating bright and dark fringes that appear on a screen when coherent waves, such as light or water waves, pass through two parallel slits. The interference pattern arises due to the superposition of wavefronts from the two slits. When the peaks of the waves from one slit coincide with the peaks from the other slit (constructive interference), bright fringes are observed. When the peaks from one slit coincide with the troughs of the waves from the other slit (destructive interference), dark fringes are observed.
On the other hand, double-slit diffraction refers to the spreading or bending of waves around obstacles or through narrow slits. Diffraction occurs when waves encounter an obstacle or a slit that is comparable in size to their wavelength. In the case of the double-slit experiment, the slits are typically narrow enough that diffraction effects become significant. The diffraction of waves causes them to spread out and interfere with each other, resulting in the interference pattern observed on the screen.
In summary, double-slit interference refers to the pattern of bright and dark fringes that arises from the superposition of waves passing through two parallel slits, while double-slit diffraction refers to the spreading or bending of waves as they pass through the slits. Both phenomena are interconnected and contribute to the overall pattern observed in the double-slit experiment.