On grinding a lens, its focal length

Options

A. increases
B. decreases
C. remains same
D. nothing can be decided

Explanation

**Step-by-Step Solution:**

1. **Understanding the Concept of Focal Length**:
- The focal length of a lens is the distance from the lens to the focal point, where parallel rays of light converge after passing through the lens.

2. **Effect of Grinding a Lens**:
- Grinding a lens involves physically altering its shape, which can change its curvature. The curvature of the lens directly affects its focal length.

3. **Determining the Change in Focal Length**:
- When a lens is ground, it typically becomes less curved (flatter). A flatter lens has a longer focal length. Therefore, grinding a lens generally results in an increase in its focal length.

4. **Understanding Power of the Lens**:
- The power of a lens (P) is defined as the inverse of its focal length (f) in meters:
\[ P = \frac{1}{f} \text{ (in diopters)} \]
- If the focal length increases due to grinding, the power of the lens will decrease.

5. **Conclusion**:
- Therefore, upon grinding a lens, its focal length increases, and consequently, its power decreases.

**Final Answer**: When a lens is ground, its focal length increases.

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