Question

An air bubble inside water behaves like a ………………….. lens.

Answer 1

Hint: Here are two types of lenses, converging and diverging lenses. So, first of all we will understand the properties of converging and diverging lenses and then based on that we will find which properties match the properties of an air bubble and then we will find the answer.

Complete step-by-step solution -
In question we are asked what does an air bubble inside after behaves like but before finding it, we will understand the type of lenses. So, there are two types of lenses converging and diverging lens, they can be defined as,
Converging lens: A lens that converts parallel rays of light to convergent rays and produces a real image. It can be seen in figure also as,

Diverging lens: A lens that converts parallel rays of light to divergent rays and produces a virtual. It can be seen in figure also as,

Now, the diverging lens also causes refraction of light and it also behaves as a concave lens. So on, considering the air bubble, when a ray of light passes through the bubble it gets refracted as the medium of travel changes.
Water is denser medium then air, so the rays of light goes away from the normal which can also be considered as divergent which is similar to diverging lens. It can be seen in figure below,

So, from this we can say that an air bubble inside the water behaves as a diverging or concave lens.

Note: As the bubble is formed inside the water, the rays entering and coming out go under divergence, but if the bubble is in the form of rain drop then the rays enter at angle to the normal due to which they get reflected completely and this phenomenon is called total internal reflection. So, we can say that the medium in which rays travel plays a very important role.