A plano convex lens has radius of curvature `10` cm. Its focal length is `80` cm under water. Calculate the refractive index of the material of the lens, given refractive index of water is `4//3`.

Explanation

To solve the problem, we need to determine the refractive index of the material of a plano-convex lens given its radius of curvature, focal length in water, and the refractive index of water.

### Step-by-Step Solution:

1. **Identify Given Values**:
- Radius of curvature of the convex surface, \( R_1 = 10 \, \text{cm} \)
- Radius of curvature of the flat surface, \( R_2 = \infty \) (since it's a plano-convex lens)
- Focal length of the lens in water, \( f = 80 \, \text{cm} \)
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