A spherical air bubble is embedded in a piece of glass. For a ray of light passing through the bubble, it behaves like a :

A spherical air bubble embedded in glass behaves as a diverging lens. Although the bubble is physically shaped like a double-convex lens, its optical behavior is determined by the relative refractive indices of the media. Light travels from glass (a denser medium with a higher refractive index) into air (a rarer medium with a lower refractive index) [t1, t4]. According to the laws of refraction, when light enters a medium with a lower refractive index, it bends away from the normal [t7]. For a spherical bubble, this geometry causes parallel incident rays to spread out or diverge upon passing through the interfaces [t1, t5]. In contrast, a standard glass convex lens in air converges light because the lens material is denser than the surrounding medium [c1, c2]. Therefore, the air bubble in glass acts as a diverging lens [t4].

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 10: Light: Mirrors and Lenses > Activity 10.10: Let us investigate > p. 164
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 9: Light – Reflection and Refraction > 9.3.3 Refraction by Spherical Lenses > p. 150