An air bubble in water will act like a

1. The question asks about the optical behavior of an air bubble in water. 2. This involves the principle of refraction, which occurs when light passes between media with different refractive indices. 3. Air has a lower refractive index (approx. 1.00) than water (approx. 1.33). 4. An air bubble in water essentially acts like a pocket of a less optically dense medium within a denser medium. The bubble typically has a spherical shape, thus presenting curved surfaces to incident light. 5. When parallel light rays from the water enter the air bubble (denser to less dense medium), they bend away from the normal. When they exit the bubble back into the water (less dense to denser medium), they bend towards the normal. 6. Due to the curvature of the bubble surfaces, the overall effect is that parallel incident rays diverge after passing through the bubble. A lens that causes parallel light to diverge is called a concave lens (or diverging lens). 7. Therefore, an air bubble in water acts like a concave lens.