Define power of a lens and give its ralation with focal length.

Explanation

### Step-by-Step Solution:

1. **Definition of Power of a Lens**:
- The power of a lens is defined as the ability of the lens to converge or diverge light rays that are incident upon it. It quantifies how strongly the lens can bend light.

2. **Mathematical Expression**:
- The power (P) of a lens is mathematically expressed as the reciprocal of its focal length (f). This can be written as:
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