Air bubble placed in water

1. Dec 12, 2011

rktpro

I was tackling a problem that came to my mind whether air bubble placed in water is converging or diverging lens.
What I have concluded is that since bubble is sphere, we can assume it to be made of two similar plano convex lens. Now both of them will have same focal length but applying convention states that one would be positive and other would be negative. Thus the effective focal length would be zero and hence it wouldn't act like a lens but a glass slab.
What do you say?

2. Dec 12, 2011

JHamm

Light will be deflected as it enters the bubble, will it necessarily contact the other edge of the sphere at the same angle as it contacted the first edge?

3. Dec 12, 2011

nasu

This is not true. The two halves are both convergent (or divergent) so their powers have the same sign. A glass ball in air does not behave like a glass slab.
To find out the character of the air bubble (or half bubble) lens you just need to trace one or two rays.

4. Dec 12, 2011

rktpro

Probably not.

5. Dec 12, 2011

rktpro

How can both be of same focal length. If we apply convention, one would be positive and one negative. Because the focal points would be in two different directions.
If they are both convergent, it would mean that the image formed would be outside the bubble?

Please illustrate with a diagram, if possible.