Air bubble inside glass

Question

A convex glass lens acts as a converging lens when the medium around it is, say, air which is rarer than glass. But what happens if a "convex air lens" is inside a glass medium? Does it act like a diverging lens?

Answer 1

You can see it in the picture. On the glass-air boundary the incident ray refracts away from the normal. On the other side of the air bubble it refracts back to the normal but since the normal is rotated with respect to the left side, the ray is further rotated away from the main axis. On the right side of the glass the ray is refracted again.

But it all depends on the shape of the glass. If the outside boundaries of the glas are more bend than the inside boundaries you could end up with a positive lens altogether.

Imagine a small sheet of glass with the same curvature outside and inside. The rays would deflect a little but but virtually no converging/diverging would occur.

Answer 2

In a word, "yes." If you dig up the formulas for ray propagation at a boundary, you'll see it immediately.

Perhaps a simpler way to visualize this situation is as two (thick) concave lenses mounted edge-to-edge. You know that each of those lenses is a diverging lens.