In a single-slit experiment, when light passes through a narrow slit, it diffracts and spreads out. This diffraction phenomenon leads to the formation of a pattern of bright and dark fringes on a screen placed behind the slit. The dark fringes, known as minima, occur at specific angles or positions where destructive interference between the diffracted waves takes place.
To understand the formation of dark fringes, let's consider the wave nature of light. When light passes through the single slit, it behaves as a wave and undergoes diffraction. Diffraction occurs because the slit acts as a secondary source of spherical wavelets that spread out from the slit's edges.
The diffracted waves interfere with each other when they reach the screen. At certain angles or positions, the peaks of one wave coincide with the troughs of another wave, resulting in destructive interference. In these regions, the amplitude of the waves cancels out, leading to the formation of dark fringes.
The specific locations of the dark fringes can be determined using the concept of path difference. The path difference is the difference in the distance traveled by waves from the edges of the slit to a particular point on the screen. If this path difference is equal to an integer multiple of the wavelength of light, destructive interference occurs, resulting in a dark fringe.
The dark fringes in a single-slit experiment are broader and less intense compared to the bright fringes. This is because the central maximum (the bright central region) is much wider than the dark fringes due to the greater contribution of waves passing through the central part of the slit.
In summary, the dark fringes in a single-slit experiment occur due to destructive interference between diffracted waves from the edges of the slit. These dark fringes are the result of specific conditions of path difference, leading to cancellation of wave amplitudes at certain angles or positions on the screen.