Define focal length of a lens and calculate focal length of the lens having radius of curvature 30 cm.

Explanation

### Step-by-Step Solution

1. **Definition of Focal Length**:
The focal length of a lens is defined as the distance between the optical center of the lens and its focal point. It is the point where parallel rays of light either converge (for a converging lens) or appear to diverge from (for a diverging lens) after passing through the lens.

2. **Understanding the Relationship**:
For a lens, the focal length (f) is related to the radius of curvature (R) of the lens surfaces. The focal length is given by the formula:
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