A spherical air bubble is embedded in a piece of glass. For a ray of light passing through the bubble, it behaves like a
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → diverging lens
Whether a lens converges or diverges depends on its shape and on the refractive index of the lens relative to the surrounding medium. By the lens maker’s formula,
\( \displaystyle \frac{1}{f} = \left(\frac{n_{\mathrm{bubble}}}{n_{\mathrm{glass}}} - 1\right)\left(\frac{1}{R_1} - \frac{1}{R_2}\right) \)
A spherical bubble has the shape of a double convex lens, so the second bracket is positive. But air is optically rarer than glass, so the first bracket is negative, and f comes out negative. A ray going from glass into air bends away from the normal at the first surface, so the bubble spreads the rays out: it acts as a diverging lens.