Question

Does an air bubble inside water behave like a lens? If so, what type of lens is it? Explain?

Answer 1

Hint: Behavior of lens depends upon the density of the medium in which light ray passes. When it passes from rare to denser or denser to rare medium, light ray bent towards normal or away from normal. So the path of light rays after entering the medium indicates the behavior of the lens.

Complete step by step answer:When the light ray enters from water to air, it is refracted so that it deviates away from normal because light ray is entering from denser medium to rarer medium.
Since air is optically rarer than water, the ray of light bends away from the normal at the point of incidence when moving from water to air while it bends towards the normal while moving from air to water. The normal at any point of a spherical bubble will pass through the center of the bubble.
It is clearly visible that the air bubble acts as a ‘diverging lens’ (concave lens) in water.
The refractive index of air, and
The refractive index of water,.
Since the water refractive index is greater than air, the air bubbles in the water will behave like a concave or diverging lens.

Note:When light rays pass through the air bubble then the behavior of the air bubble acts as a concave lens. But in case of rain drop the ray enters at an angle to the normal due to which they get reflected completely and this phenomenon is called total internal reflection. So, we can say that medium in which rays travel plays a very important role. So the phenomenon of total internal reflection and nature of lenses is totally different.