Define: Radius of curvature and centre of curvature

Explanation

### Step-by-Step Solution

1. **Define Center of Curvature**:
- The center of curvature is defined as the center of the hollow sphere of which the spherical mirror is a part.
- If we visualize a spherical mirror, it is essentially a segment of a larger sphere. The center of this larger sphere is what we refer to as the center of curvature.

2. **Visual Representation**:
- Imagine a hollow sphere. When a portion of this sphere is polished to create a mirror (either on the inside or outside), the center of that sphere remains the center of curvature for the mirror.
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