The radius of curvature of the faces of a double convex lens are `10 cm and 15 cm`. If focal length of lens of lens is `12 cm`, find the refractive index of the material of the lens.

Explanation

To find the refractive index of the material of a double convex lens with given radii of curvature and focal length, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the given values:**
- Radius of curvature of the first surface, \( R_1 = 10 \, \text{cm} \)
- Radius of curvature of the second surface, \( R_2 = -15 \, \text{cm} \) (negative because it is convex towards the incoming light)
- Focal length, \( f = 12 \, \text{cm} \)
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