Air bubble in water behaves as

Options

A. sometimes concave, somethimes convex lens
B. concavc lens
C. convex lens
D. always refraction surface

Explanation

To determine how an air bubble in water behaves, we can analyze it using the lens maker's formula and the properties of lenses.

### Step-by-Step Solution:

1. **Identify the Mediums**:
- The air bubble is surrounded by water. The refractive index (μ) of air is approximately 1, and the refractive index of water is approximately 1.33.

2. **Use the Lens Maker's Formula**:
- The lens maker's formula is given by:
\[ \frac{1}{f} = \left( \mu - 1 \right) \left( \frac{1}{R_1} - \frac{1}{R_2} \right) \]
- Here, \( \mu \) is the refractive index of the medium surrounding the lens (water in this case), and \( R_1 \) and \( R_2 \) are the radii of curvature of the two surfaces of the lens.

3. **Assign Values**:
- For the air bubble in water:
- \( \mu = 1 \) (for air)
- \( \mu_{water} = 1.33 \)
- Assume the radius of curvature \( R_1 = r \) (the surface of the bubble facing the water) and \( R_2 = -r \) (the surface of the bubble facing away from the water).

4. **Substitute into the Formula**:
- Substitute the values into the lens maker's formula:
\[ \frac{1}{f} = \left( 1.33 - 1 \right) \left( \frac{1}{r} - \frac{1}{-r} \right) \]
- This simplifies to:
\[ \frac{1}{f} = 0.33 \left( \frac{1}{r} + \frac{1}{r} \right) = 0.33 \left( \frac{2}{r} \right) = \frac{0.66}{r} \]

5. **Determine the Focal Length**:
- Rearranging gives:
\[ f = \frac{r}{0.66} \]
- Since the focal length \( f \) is positive, this indicates that the air bubble behaves like a lens.

6. **Determine the Type of Lens**:
- Since the focal length is positive and the air bubble is surrounded by a denser medium (water), it acts as a concave lens.

### Final Conclusion:
- An air bubble in water behaves like a concave lens.