A biconvex lens has focal length `(2)/(3)` times the radius of curvature of either surface. Calculate refraction index f material of the lens.

Explanation

To solve the problem of finding the refractive index of a biconvex lens given that its focal length is \( \frac{2}{3} \) times the radius of curvature, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Let the radius of curvature of each surface of the lens be \( R \).
- The focal length \( f \) is given as:
\[
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