Interference patterns observed in a double-slit experiment arise from the superposition of waves emanating from two closely spaced slits.

In a typical double-slit experiment, light is directed through two narrow slits, which serve as separate sources of waves. As these waves propagate, they overlap and interact with one another, resulting in an interference pattern characterized by alternating bright and dark bands, known as fringes, on a screen positioned behind the slits.

The bright fringes occur due to constructive interference, which happens when the waves from the two slits arrive in phase—meaning their peaks and troughs align perfectly. This alignment causes their amplitudes to combine, leading to an increased light intensity. Conversely, the dark fringes result from destructive interference, which takes place when the waves arrive out of phase. In this scenario, the peak of one wave coincides with the trough of another, causing their amplitudes to cancel each other out and resulting in no light being detected.

The positions of these fringes can be accurately predicted using the principle of superposition and the wave nature of light. Specifically, the path difference between the waves traveling from the two slits plays a crucial role in determining whether the interference will be constructive or destructive. When the path difference is an integer multiple of the wavelength, the waves arrive in phase and interfere constructively, producing a bright fringe. Conversely, when the path difference is a half-integer multiple of the wavelength, the waves arrive out of phase and interfere destructively, resulting in a dark fringe.

The double-slit experiment serves as a fundamental illustration of the wave-particle duality inherent in light and other quantum particles. It demonstrates that entities such as light and electrons exhibit both wave-like and particle-like behaviors. When the slits are examined individually, they behave as particles; however, when observed in conjunction, they interfere as waves, generating an interference pattern. This phenomenon cannot be explained by classical physics and stands as a cornerstone of quantum mechanics.