An air bubble is formed inside the water does it acts as a converging lens or diverging lens. calculate its focal length?
Answers
Answer:
Explanation:
The standard answer is, a bubble is a sphere, and the source of light is outside the sphere. Light from outside strikes on the convex surface of the sphere, therefore, air bubbles act as a convex lens.
However, the correct answer is just the opposite.
If we compare a convex air bubble and a concave lens made of glass, we can see that the interaction between the water-and-air in the bubble, and the glass-and-air in the lens is identical. The refractive index of air is around 1.0003 whereas the refractive index of water is 1.333 and the average refractive index of glass is around 1.500. We can see that the material with the higher index (water or glass) curves in and the material with the lower index of refraction (air) curves out. The bubble can be seen as two concaves facing each other, whereas in the lens made of glass, the two concaves are in tandem. Therefore, though the bubble is convex it should behave like a concave lens.