When a convex lens is immersed in water, its capacity changes. The refractive index of water is higher than that of air, altering how light passes through the lens. This change causes the lens to bend light more sharply, affecting its focal length. Consequently, the focal length of the lens decreases when immersed in water. This phenomenon is due to the difference in refractive indices between air and water, where light travels slower in water than in air, causing greater refraction. As a result, the lens’s ability to converge light rays diminishes, affecting its optical performance underwater. Understanding this effect is essential in underwater optics, such as designing lenses for underwater cameras or correcting vision in aquatic environments. Therefore, when a convex lens is immersed in water, its capacity decreases due to the altered refractive conditions compared to air.