Define the following terms in the context of spherical mirrors: Principal focus

Explanation

### Step-by-Step Solution:

1. **Understanding Spherical Mirrors**:
- Spherical mirrors are mirrors that are shaped like a portion of a sphere. They can be either concave (curved inward) or convex (curved outward).

2. **Identifying the Principal Axis**:
- The principal axis is an imaginary line that runs horizontally through the center of the mirror, dividing it into two equal halves. It is the line along which light rays are typically analyzed.

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