Why central spot is present bright in newtonrings?

The central spot in Newton's rings appears bright due to constructive interference of light waves reflecting from the top and bottom surfaces of a thin air film created between a convex lens and a flat glass surface. At the center, the path difference between the two reflected waves is zero or an integer multiple of the wavelength, leading to constructive interference. This results in the central spot being bright, while other rings appear dark or bright depending on the varying path differences as you move away from the center.