91Ó°ÊÓ

When light encounters an obstacle or a slit that is comparable in size to its wavelength, it bends around the edges forming a unique light pattern on a screen. This phenomenon is called diffraction. When we project diffracted light from a single slit onto a screen, a distinct pattern emerges comprising a bright spot at the center known as the central maximum, and several less intense, spaced out bright and dark areas known as minima and maxima respectively.
The formation of such patterns arises due to the interference of light waves emanating through different parts of the slit. The spacing and intensity of the patterns depend heavily on factors like the wavelength of light and the slit width, indicating how a small change in any of these can dramatically alter the viewable diffraction pattern on the screen.

The central maximum is the brightest point in a single slit diffraction pattern. It appears as the peak in the middle of the pattern and is the result of constructive interference of light rays passing directly through the slit at normal incidence. This region gets more light intensity compared to the neighboring areas because all paths through the slit contribute to the central point in-phase at the center of the screen.
If you imagine slicing the light waves into parts, each part would align perfectly when they meet in this central zone, causing the brightness to peak here. The central maximum is always at zero degrees angle and typically has the highest intensity.

Moving outward from the central maximum, the first point where the light intensity drops to zero is known as the first minimum. This occurs because the light rays from different parts of the slit interfere destructively at this angle, effectively canceling each other out. For a single slit, this is mathematically represented by the condition \( a \sin \theta = \lambda \), where \( a \) is the slit width, \( \theta \) is the angular position of the first minimum, and \( \lambda \) is the wavelength of the light.
Calculating the position on a screen, especially with a lens in place, involves transforming this angular advice into a linear distance using \( y = f \tan \theta \). For small angles, \( \tan \theta \approx \sin \theta \), thus giving a manageable approximation to find this first dim spot.

The second minimum is further from the central maximum and is the next point of zero light intensity beyond the first minimum. It is the result of continued destructive interference at a larger angle, effectively twice that of the first minimum. The mathematical description follows the condition \( a \sin \theta = 2\lambda \), using the same symbols as for the first minimum.
On the screen, as light travels further, the disrupted light paths continue to cancel each other out precisely at these minima, forming dark spots. Calculating the distance between sequential minima (such as from the first to the second) becomes a geometric progression using the above conditions, which determines not only the pattern but also spacing on the screen.